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Medow MS, Guber K, Chokshi S, Terilli C, Visintainer P, Stewart JM. The Benefits of Oral Rehydration on Orthostatic Intolerance in Children with Postural Tachycardia Syndrome. J Pediatr 2019; 214:96-102. [PMID: 31405524 PMCID: PMC6815702 DOI: 10.1016/j.jpeds.2019.07.041] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 07/11/2019] [Accepted: 07/15/2019] [Indexed: 11/18/2022]
Abstract
OBJECTIVE To evaluate whether equal volumes of oral rehydration solution (ORS) or intravenous (IV) saline provide similar improvements in cardiovascular status during controlled orthostatic challenge when administered to subjects with postural tachycardia syndrome (POTS) with orthostatic intolerance. STUDY DESIGN We studied the neurovascular response to fluid loading during orthostatic stress using lower body negative pressure (LBNP) in 10 subjects with POTS with orthostatic intolerance and 15 controls, and on subsequent days before and 1 hour after IV saline infusion or ingestion of ORS. RESULTS Subjects with POTS exhibited reduced tolerance to LBNP (P < .0001) compared with controls (Orthostatic Index of 35 715 ± 3469 vs 93 980 ± 7977, respectively). In POTS, following ORS but not saline infusion, cerebral blood flow velocity (CBFv) was significantly higher than that with no treatment, at -45 mm Hg (P < .0005). Although fluid loading did not confer any advantage in controls, subjects with POTS experienced a significant improvement in orthostatic tolerance following both saline infusion (100 ± 9.7 vs 134.5 ± 17.4; P < .05) and ORS (100 ± 9.7 vs 155.6 ± 15.7; P < .001) when evaluated by normalized orthostatic index (P < .001, compared with untreated baseline). CONCLUSIONS Maintenance of CBFv may have resulted in the improved short-term orthostatic tolerance exhibited by the subjects with POTS following ORS administration. ORS is a convenient, safe, and effective therapy for short-term relief of orthostatic intolerance.
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Affiliation(s)
- Marvin S Medow
- Department of Pediatrics, New York Medical College, Valhalla, NY; Department of Physiology, New York Medical College, Valhalla, NY.
| | | | | | - Courtney Terilli
- Department of Pediatrics, New York Medical College, Valhalla, NY
| | - Paul Visintainer
- Department of Epidemiology and Biostatistics, Baystate Medical Center, University of Massachusetts School of Medicine, Worcester, MA
| | - Julian M Stewart
- Department of Pediatrics, New York Medical College, Valhalla, NY; Department of Physiology, New York Medical College, Valhalla, NY
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Hoff IE, Hisdal J, Landsverk SA, Røislien J, Kirkebøen KA, Høiseth LØ. Respiratory variations in pulse pressure and photoplethysmographic waveform amplitude during positive expiratory pressure and continuous positive airway pressure in a model of progressive hypovolemia. PLoS One 2019; 14:e0223071. [PMID: 31560715 PMCID: PMC6764667 DOI: 10.1371/journal.pone.0223071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 09/12/2019] [Indexed: 11/18/2022] Open
Abstract
PURPOSE Respiratory variations in pulse pressure (dPP) and photoplethysmographic waveform amplitude (dPOP) are used for evaluation of volume status in mechanically ventilated patients. Amplification of intrathoracic pressure changes may enable their use also during spontaneous breathing. We investigated the association between the degree of hypovolemia and dPP and dPOP at different levels of two commonly applied clinical interventions; positive expiratory pressure (PEP) and continuous positive airway pressure (CPAP). METHODS 20 healthy volunteers were exposed to progressive hypovolemia by lower body negative pressure (LBNP). PEP of 0 (baseline), 5 and 10 cmH2O was applied by an expiratory resistor and CPAP of 0 (baseline), 5 and 10 cmH2O by a facemask. dPP was obtained non-invasively with the volume clamp method and dPOP from a pulse oximeter. Central venous pressure was measured in 10 subjects. Associations between changes were examined using linear mixed-effects regression models. RESULTS dPP increased with progressive LBNP at all levels of PEP and CPAP. The LBNP-induced increase in dPP was amplified by PEP 10 cmH20. dPOP increased with progressive LBNP during PEP 5 and PEP 10, and during all levels of CPAP. There was no additional effect of the level of PEP or CPAP on dPOP. Progressive hypovolemia and increasing levels of PEP were reflected by increasing respiratory variations in CVP. CONCLUSION dPP and dPOP reflected progressive hypovolemia in spontaneously breathing healthy volunteers during PEP and CPAP. An increase in PEP from baseline to 10 cmH2O augmented the increase in dPP, but not in dPOP.
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Affiliation(s)
- Ingrid Elise Hoff
- Norwegian Air Ambulance Foundation, Sentrum, Oslo, Norway
- Department of Anesthesiology, Oslo University Hospital, Nydalen, Oslo, Norway
- * E-mail:
| | - Jonny Hisdal
- Section of Vascular Investigations, Department of Vascular Surgery, Oslo University Hospital, Nydalen, Oslo, Norway
- Faculty of Medicine, University of Oslo, Blindern, Oslo, Norway
| | | | - Jo Røislien
- Norwegian Air Ambulance Foundation, Sentrum, Oslo, Norway
| | | | - Lars Øivind Høiseth
- Department of Anesthesiology, Oslo University Hospital, Nydalen, Oslo, Norway
- Section of Vascular Investigations, Department of Vascular Surgery, Oslo University Hospital, Nydalen, Oslo, Norway
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Comparisons of Traditional Metabolic Markers and Compensatory Reserve as Early Predictors of Tolerance to Central Hypovolemia in Humans. Shock 2019; 50:71-77. [PMID: 29049136 DOI: 10.1097/shk.0000000000001034] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Circulatory shock remains a leading cause of death in both military and civilian trauma. Early, accurate and reliable prediction of decompensation is necessary for the most efficient interventions and clinical outcomes. Individual tolerance to reduced central blood volume can serve as a model to assess the sensitivity and specificity of vital sign measurements. The compensatory reserve (CRM) is the measurement of this capacity. Measurements of muscle oxygen saturation (SmO2), blood lactate, and end tidal CO2 (EtCO2) have recently gained attention as prognostic tools for early assessment of the status of patients with progressive hemorrhage, but lack the ability to adequately differentiate individual tolerance to hypovolemia. We hypothesized that the CRM would better predict hemodynamic decompensation and provide greater specificity and sensitivity than metabolic measures. To test this hypothesis, we employed lower body negative pressure on healthy human subjects until symptoms of presyncope were evident. Receiver operating characteristic area under the curve (ROC AUC), sensitivity, and specificity were used to evaluate the ability of CRM, partial pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), SmO2, lactate, EtCO2, potential of hydrogen (pH), base excess and hematocrit (Hct) to predict hemodynamic decompensation. The ROC AUC for CRM (0.94) had a superior ability to predict decompensation compared with pO2 (0.85), pCO2 (0.62), SmO2 (0.72), lactate (0.57), EtCO2 (0.74), pH (0.55), base excess (0.59), and Hct (0.67). Similarly, CRM also exhibited the greatest sensitivity and specificity. These findings support the notion that CRM provides superior detection of hemodynamic compensation compared with commonly used clinical metabolic measures.
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Measurement of compensatory reserve predicts racial differences in tolerance to simulated hemorrhage in women. J Trauma Acute Care Surg 2019; 85:S77-S83. [PMID: 29443858 DOI: 10.1097/ta.0000000000001837] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
BACKGROUND The compensatory reserve measurement (CRM) has been established to accurately measure the body's total integrated capacity to compensate for physiologic states of reduced central blood volume and predict hemodynamic decompensation associated with inadequate tissue oxygenation. We previously demonstrated that African American (AA) women have a higher tolerance to reductions in central blood volume. Therefore, we tested the hypothesis that the CRM would identify racial differences during simulated hemorrhage, before the onset of traditional signs/symptoms. METHODS We performed a retrospective analysis during simulated hemorrhage using lower-body negative pressure (LBNP) in 23 AA (22 ± 1 years; 24 ± 1 kg/m) and 31 white women (WW) (20 ± 1 years; 23 ± 1 kg/m). Beat-by-beat blood pressure (BP) and heart rate (HR) were recorded during progressive lower body negative pressure to presyncope. The BP waveforms were analyzed using a machine-learning algorithm to derive the CRM at each lower body negative pressure stage. RESULTS Resting mean arterial BP (AA, 78 ± 3 mm Hg vs. WW, 74 ± 2 mm Hg) and HR (AA, 68 ± 2 bpm vs. WW, 65 ± 2 bpm) were similar between groups. The CRM progressively decreased during LBNP in both groups; however, the rate of decline in the CRM was less (p < 0.05) in AA. The CRM was 4% higher in AA at -15 mm Hg LBNP and progressively increased to 21% higher at -50 mm Hg LBNP (p < 0.05). However, changes in BP and HR were not different between groups. CONCLUSION These data support the notion that the greater tolerance to simulated hemorrhage induced by LBNP in AA women can be explained by their greater capacity to protect the reserve to compensate for progressive central hypovolemia compared with WW, independent of standard vital signs. LEVEL OF EVIDENCE Diagnostic test, level II.
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Hydration Status and Cardiovascular Function. Nutrients 2019; 11:nu11081866. [PMID: 31405195 PMCID: PMC6723555 DOI: 10.3390/nu11081866] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2019] [Revised: 07/30/2019] [Accepted: 08/08/2019] [Indexed: 02/07/2023] Open
Abstract
Hypohydration, defined as a state of low body water, increases thirst sensations, arginine vasopressin release, and elicits renin–angiotensin–aldosterone system activation to replenish intra- and extra-cellular fluid stores. Hypohydration impairs mental and physical performance, but new evidence suggests hypohydration may also have deleterious effects on cardiovascular health. This is alarming because cardiovascular disease is the leading cause of death in the United States. Observational studies have linked habitual low water intake with increased future risk for adverse cardiovascular events. While it is currently unclear how chronic reductions in water intake may predispose individuals to greater future risk for adverse cardiovascular events, there is evidence that acute hypohydration impairs vascular function and blood pressure (BP) regulation. Specifically, acute hypohydration may reduce endothelial function, increase sympathetic nervous system activity, and worsen orthostatic tolerance. Therefore, the purpose of this review is to present the currently available evidence linking acute hypohydration with altered vascular function and BP regulation.
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Hisdal J, Landsverk SA, Hoff IE, Hagen OA, Kirkebøen KA, Høiseth LØ. Associations between changes in precerebral blood flow and cerebral oximetry in the lower body negative pressure model of hypovolemia in healthy volunteers. PLoS One 2019; 14:e0219154. [PMID: 31251778 PMCID: PMC6599124 DOI: 10.1371/journal.pone.0219154] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2019] [Accepted: 06/17/2019] [Indexed: 11/19/2022] Open
Abstract
Reductions in cerebral oxygen saturation (ScO2) measured by near infra-red spectroscopy have been found during compensated hypovolemia in the lower body negative pressure (LBNP)-model, which may reflect reduced cerebral blood flow. However, ScO2 may also be contaminated from extracranial (scalp) tissues, mainly supplied by the external carotid artery (ECA), and it is possible that a ScO2 reduction during hypovolemia is caused by reduced scalp, and not cerebral, blood flow. The aim of the present study was to explore the associations between blood flow in precerebral arteries and ScO2 during LBNP-induced hypovolemia. Twenty healthy volunteers were exposed to LBNP 20, 40, 60 and 80 mmHg. Blood flow in the internal carotid artery (ICA), ECA and vertebral artery (VA) was measured by Doppler ultrasound. Stroke volume for calculating cardiac output was measured by suprasternal Doppler. Associations of changes within subjects were examined using linear mixed-effects regression models. LBNP reduced cardiac output, ScO2 and ICA and ECA blood flow. Changes in flow in both ICA and ECA were associated with changes in ScO2 and cardiac output. Flow in the VA did not change during LBNP and changes in VA flow were not associated with changes in ScO2 or cardiac output. During experimental compensated hypovolemia in healthy, conscious subjects, a reduced ScO2 may thus reflect a reduction in both cerebral and extracranial blood flow.
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Affiliation(s)
- Jonny Hisdal
- Section of Vascular Investigations, Department of Vascular Surgery, Division of Cardiovascular and Pulmonary Diseases, Oslo University Hospital, Oslo, Norway
- Faculty of Medicine, University of Oslo, Oslo, Norway
| | - Svein Aslak Landsverk
- Department of Anesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital, Oslo, Norway
| | - Ingrid Elise Hoff
- Department of Anesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital, Oslo, Norway
- Norwegian Air Ambulance Foundation, Oslo, Norway
| | - Ove Andreas Hagen
- Department of Anesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital, Oslo, Norway
| | - Knut Arvid Kirkebøen
- Faculty of Medicine, University of Oslo, Oslo, Norway
- Department of Anesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital, Oslo, Norway
| | - Lars Øivind Høiseth
- Section of Vascular Investigations, Department of Vascular Surgery, Division of Cardiovascular and Pulmonary Diseases, Oslo University Hospital, Oslo, Norway
- Department of Anesthesiology, Division of Emergencies and Critical Care, Oslo University Hospital, Oslo, Norway
- * E-mail:
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Convertino VA. Mechanisms of inspiration that modulate cardiovascular control: the other side of breathing. J Appl Physiol (1985) 2019; 127:1187-1196. [PMID: 31225967 DOI: 10.1152/japplphysiol.00050.2019] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The objective of this minireview is to describe the physiology and potential clinical benefits derived from inspiration. Recent animal and clinical studies demonstrate that one of the body's natural mechanisms associated with inspiration is to harness the respiratory pump to enhance circulation to vital organs. There is evidence that large reductions in intrathoracic pressure (>20 cmH2O) caused by some inspiration maneuvers (e.g., Mueller maneuver) or pathophysiology (e.g., heart failure, chronic obstructive lung disease) can result in adverse hemodynamic effects. However, the respiratory pump can improve cardiovascular functions when a "sweet spot" for generation of negative intrathoracic pressure during inspiration can be maintained at or less than 10 cmH2O below normal inspiration. These beneficial physiological effects include greater cardiac filling and output, lower intracranial pressure, cardiac baroreflex resetting, greater cerebral blood flow oscillatory patterns, increased vascular pressure gradients, and promoting sustained feedback between sympathetic nerve activity and arterial pressure. In addition to promoting gas exchange, data obtained from numerous animal and human experiments have provided new insights into "the other side of breathing": the modulation of circulation by reduced intrathoracic pressure generated during inspiration. The translation of these physiological relationships form the basis for the development and application of technologies designed to optimize the intrathoracic pump for treatment of clinical conditions associated with hypovolemia including cardiac arrest, orthostatic hypotension, hemorrhagic shock, and traumatic brain injury. Harnessing these fundamental mechanisms that control cardiopulmonary physiology provides opportunities to use inspiration as a potential tool to help treat significant and often life-threatening circulatory disorders.
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Affiliation(s)
- Victor A Convertino
- Battlefield Health & Trauma Center for Human Integrative Physiology, U.S. Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
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Cvirn G, Waha JE, Brix B, Rössler A, Jantscher A, Schlagenhauf A, Koestenberger M, Wonisch W, Wagner T, Goswami N. Coagulation changes induced by lower-body negative pressure in men and women. J Appl Physiol (1985) 2019; 126:1214-1222. [DOI: 10.1152/japplphysiol.00940.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
We investigated whether lower-body negative pressure (LBNP) application leads to coagulation activation in whole blood (WB) samples in healthy men and women. Twenty-four women and 21 men, all healthy young participants, with no histories of thrombotic disorders and not on medications, were included. LBNP was commenced at −10 mmHg and increased by −10 mmHg every 5 min until a maximum of −40 mmHg. Recovery up to 10 min was also monitored. Blood samples were collected at baseline, at end of LBNP, and end of recovery. Hemostatic profiling included comparing the effects of LBNP on coagulation values in both men and women using standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and markers of thrombin formation. LBNP led to coagulation activation determined in both plasma and WB samples. At baseline, women were hypercoagulable compared with men, as evidenced by their shorter “lag times” and higher thrombin peaks and by shorter “coagulation times” and “clot formation times.” Moreover, men were more susceptible to LBNP, as reflected in their elevated factor VIII levels and decreased lag times following LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. Women appear to be relatively hypercoagulable compared with men, but men are more susceptible to coagulation changes during LBNP. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.NEW & NOTEWORTHY LBNP led to coagulation activation determined in both plasma and whole blood samples. At baseline, women were hypercoagulable compared with men. Men were, however, more susceptible to coagulation changes during LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.
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Affiliation(s)
- Gerhard Cvirn
- Physiological Chemistry Division, Otto Loewi Research Center, Medical University of Graz, Graz, Austria
| | - James E. Waha
- Physiology Division, Otto Loewi Research Center, Medical University of Graz, Graz, Austria
| | - Bianca Brix
- Physiology Division, Otto Loewi Research Center, Medical University of Graz, Graz, Austria
| | - Andreas Rössler
- Physiology Division, Otto Loewi Research Center, Medical University of Graz, Graz, Austria
| | - Andreas Jantscher
- Physiology Division, Otto Loewi Research Center, Medical University of Graz, Graz, Austria
| | - Axel Schlagenhauf
- Department of Pediatric Cardiology, Medical University of Graz, Graz, Austria
| | | | - Willibald Wonisch
- Physiological Chemistry Division, Otto Loewi Research Center, Medical University of Graz, Graz, Austria
| | - Thomas Wagner
- Department of Blood Group Serology and Transfusion Medicine, Medical University of Graz, Graz, Austria
| | - Nandu Goswami
- Physiology Division, Otto Loewi Research Center, Medical University of Graz, Graz, Austria
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Arterial waveform morphomics during hemorrhagic shock. Eur J Trauma Emerg Surg 2019; 47:325-332. [DOI: 10.1007/s00068-019-01140-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2018] [Accepted: 04/17/2019] [Indexed: 11/26/2022]
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Park FS, Kay VL, Sprick JD, Rosenberg AJ, Anderson GK, Mallet RT, Rickards CA. Hemorrhage simulated by lower body negative pressure provokes an oxidative stress response in healthy young adults. Exp Biol Med (Maywood) 2019; 244:272-278. [PMID: 30727766 DOI: 10.1177/1535370219828706] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
IMPACT STATEMENT We characterize the systemic oxidative stress response in young, healthy human subjects with exposure to simulated hemorrhage via application of lower body negative pressure (LBNP). Prior work has demonstrated that LBNP and actual blood loss evoke similar hemodynamic and immune responses (i.e. white blood cell count), but it is unknown whether LBNP elicits oxidative stress resembling that produced by blood loss. We show that LBNP induces a 29% increase in F2-isoprostanes, a systemic marker of oxidative stress. The findings of this investigation may have important implications for the study of hemorrhage using LBNP, including future assessments of targeted interventions that may reduce oxidative stress, such as novel fluid resuscitation approaches.
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Affiliation(s)
- Flora S Park
- 1 Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort, TX 76107, USA
| | - Victoria L Kay
- 1 Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort, TX 76107, USA
| | - Justin D Sprick
- 1 Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort, TX 76107, USA.,2 Division of Renal Medicine, Department of Medicine, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Alexander J Rosenberg
- 1 Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort, TX 76107, USA
| | - Garen K Anderson
- 1 Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort, TX 76107, USA
| | - Robert T Mallet
- 1 Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort, TX 76107, USA
| | - Caroline A Rickards
- 1 Department of Physiology & Anatomy, University of North Texas Health Science Center, Fort, TX 76107, USA
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Goswami N, Blaber AP, Hinghofer-Szalkay H, Convertino VA. Lower Body Negative Pressure: Physiological Effects, Applications, and Implementation. Physiol Rev 2019; 99:807-851. [PMID: 30540225 DOI: 10.1152/physrev.00006.2018] [Citation(s) in RCA: 117] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
This review presents lower body negative pressure (LBNP) as a unique tool to investigate the physiology of integrated systemic compensatory responses to altered hemodynamic patterns during conditions of central hypovolemia in humans. An early review published in Physiological Reviews over 40 yr ago (Wolthuis et al. Physiol Rev 54: 566-595, 1974) focused on the use of LBNP as a tool to study effects of central hypovolemia, while more than a decade ago a review appeared that focused on LBNP as a model of hemorrhagic shock (Cooke et al. J Appl Physiol (1985) 96: 1249-1261, 2004). Since then there has been a great deal of new research that has applied LBNP to investigate complex physiological responses to a variety of challenges including orthostasis, hemorrhage, and other important stressors seen in humans such as microgravity encountered during spaceflight. The LBNP stimulus has provided novel insights into the physiology underlying areas such as intolerance to reduced central blood volume, sex differences concerning blood pressure regulation, autonomic dysfunctions, adaptations to exercise training, and effects of space flight. Furthermore, approaching cardiovascular assessment using prediction models for orthostatic capacity in healthy populations, derived from LBNP tolerance protocols, has provided important insights into the mechanisms of orthostatic hypotension and central hypovolemia, especially in some patient populations as well as in healthy subjects. This review also presents a concise discussion of mathematical modeling regarding compensatory responses induced by LBNP. Given the diverse applications of LBNP, it is to be expected that new and innovative applications of LBNP will be developed to explore the complex physiological mechanisms that underline health and disease.
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Affiliation(s)
- Nandu Goswami
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
| | - Andrew Philip Blaber
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
| | - Helmut Hinghofer-Szalkay
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
| | - Victor A Convertino
- Physiology Section, Otto Loewi Research Center for Vascular Biology, Immunology and Inflammation, Medical University of Graz , Graz , Austria ; Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, British Columbia , Canada ; Battlefield Health & Trauma Center for Human Integrative Physiology, Combat Casualty Care Research Program, US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas
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Clinical evidence of autonomic dysfunction due to atrial fibrillation: implications for rhythm control strategy. J Interv Card Electrophysiol 2019; 54:299-307. [PMID: 30661160 DOI: 10.1007/s10840-019-00508-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2018] [Accepted: 01/01/2019] [Indexed: 12/11/2022]
Abstract
PURPOSE The role of the autonomic nervous system in the genesis of atrial fibrillation (AF) has been well studied; however, the converse remains poorly understood. Pulmonary veins (PV) contain receptors important in cardiac reflexes. Here, we evaluated reflex responses in patients with paroxysmal AF (PAF) to lower body negative pressure (LBNP). METHODS Thirty-four PAF patients (including 14 PAF patients post successful PV Isolation; PVI) were compared to 14 age and sex-matched controls. Mean arterial pressure (MAP), heart rate (HR), systemic vascular resistance index (SVRI), cardiac index (CI), and stroke volume index (SVI) were measured continuously during - 0, - 20, and - 40 mmHg LBNP. LBNP reduces venous return, deactivating atrial receptors, thereby eliciting a reflex increase in SVRI to maintain MAP. RESULTS AF patients have higher BMI than the controls (p = 0.02). In control subjects, LBNP did not alter MAP as SVRI increased. In PAF patients, LBNP resulted in a reduction in MAP (- 4.8%) with attenuated SVRI response (+ 4.2%) compared to controls (p < 0.05). However, in the post-PVI group, SVRI increase was similar to controls (p = 0.12) although that was insufficient to maintain MAP. In all patients, both reduction in SVI and CI and increase in HR were similar in response to LBNP. CONCLUSIONS This study provides novel clinical evidence of autonomic dysfunction in PAF patients. Successful PVI results in partial recovery of the cardiac reflex. Therefore, not only does autonomic disturbance predispose to AF but it is also a consequence of AF; potentially contributing to disease progression. This could help explain the dictum "AF begets AF."
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Crandall CG, Rickards CA, Johnson BD. Impact of environmental stressors on tolerance to hemorrhage in humans. Am J Physiol Regul Integr Comp Physiol 2018; 316:R88-R100. [PMID: 30517019 DOI: 10.1152/ajpregu.00235.2018] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hemorrhage is a leading cause of death in military and civilian settings, and ~85% of potentially survivable battlefield deaths are hemorrhage-related. Soldiers and civilians are exposed to a number of environmental and physiological conditions that have the potential to alter tolerance to a hemorrhagic insult. The objective of this review is to summarize the known impact of commonly encountered environmental and physiological conditions on tolerance to hemorrhagic insult, primarily in humans. The majority of the studies used lower body negative pressure (LBNP) to simulate a hemorrhagic insult, although some studies employed incremental blood withdrawal. This review addresses, first, the use of LBNP as a model of hemorrhage-induced central hypovolemia and, then, the effects of the following conditions on tolerance to LBNP: passive and exercise-induced heat stress with and without hypohydration/dehydration, exposure to hypothermia, and exposure to altitude/hypoxia. An understanding of the effects of these environmental and physiological conditions on responses to a hemorrhagic challenge, including tolerance, can enable development and implementation of targeted strategies and interventions to reduce the impact of such conditions on tolerance to a hemorrhagic insult and, ultimately, improve survival from blood loss injuries.
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Affiliation(s)
- Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center , Dallas, Texas
| | - Caroline A Rickards
- Department of Physiology and Anatomy, University of North Texas Health Science Center , Fort Worth, Texas
| | - Blair D Johnson
- Department of Exercise and Nutrition Sciences, University at Buffalo , Buffalo, New York
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Huang M, Brothers RM, Ganio MS, Lucas RAI, Cramer MN, Moralez G, Convertino VA, Crandall CG. Tolerance to a haemorrhagic challenge during heat stress is improved with inspiratory resistance breathing. Exp Physiol 2018; 103:1243-1250. [PMID: 29947436 PMCID: PMC6119106 DOI: 10.1113/ep087102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Accepted: 06/22/2018] [Indexed: 02/06/2023]
Abstract
NEW FINDINGS What is the central question of this study? Does inspiratory resistance breathing improve tolerance to simulated haemorrhage in individuals with elevated internal temperatures? What is the main finding and its importance? The main finding of this study is that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress. These findings demonstrate a scenario in which exploitation of the respiratory pump can ameliorate serious conditions related to systemic hypotension. ABSTRACT Heat exposure impairs human blood pressure control and markedly reduces tolerance to a simulated haemorrhagic challenge. Inspiratory resistance breathing enhances blood pressure control and improves tolerance during simulated haemorrhage in normothermic individuals. However, it is unknown whether similar improvements occur with this manoeuvre in heat stress conditions. In this study, we tested the hypothesis that inspiratory resistance breathing improves tolerance to simulated haemorrhage in individuals with elevated internal temperatures. On two separate days, eight subjects performed a simulated haemorrhage challenge [lower-body negative pressure (LBNP)] to presyncope after an increase in internal temperature of 1.3 ± 0.1°C. During one trial, subjects breathed through an inspiratory impedance device set at 0 cmH2 O of resistance (Sham), whereas on a subsequent day the device was set at -7 cmH2 O of resistance (ITD). Tolerance was quantified as the cumulative stress index. Subjects were more tolerant to the LBNP challenge during the ITD protocol, as indicated by a > 30% larger cumulative stress index (Sham, 520 ± 306 mmHg min; ITD, 682 ± 324 mmHg min; P < 0.01). These data indicate that inspiratory resistance breathing modestly improves tolerance to a simulated progressive haemorrhagic challenge during heat stress.
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Affiliation(s)
- Mu Huang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Health Care Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - R Matthew Brothers
- Department of Kinesiology, University of Texas, Arlington, Arlington, TX, USA
| | - Matthew S Ganio
- Department of Health, Human Performance and Recreation, University of Arkansas, Fayetteville, AR, USA
| | - Rebekah A I Lucas
- School of Sport, Exercise & Rehabilitation Sciences, The University of Birmingham, Edgbaston, Birmingham, UK
| | - Matthew N Cramer
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Gilbert Moralez
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | | | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX, USA
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Trotter CE, Pizzey FK, Batterson PM, Jacobs RA, Pearson J. Small reductions in skin temperature after onset of a simulated hemorrhagic challenge improve tolerance in exercise heat-stressed individuals. Am J Physiol Regul Integr Comp Physiol 2018; 315:R539-R546. [DOI: 10.1152/ajpregu.00182.2018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated whether small reductions in skin temperature 60 s after the onset of a simulated hemorrhagic challenge would improve tolerance to lower body negative pressure (LBNP) after exercise heat stress. Eleven healthy subjects completed two trials (High and Reduced). Subjects cycled at ~55% maximal oxygen uptake wearing a warm water-perfused suit until core temperatures increased by ~1.2°C before lying supine and undergoing LBNP to presyncope. LBNP tolerance was quantified as cumulative stress index (CSI; product of each LBNP level multiplied by time; mmHg·min). Skin temperature was similarly elevated from baseline before LBNP and remained elevated 60 s after the onset of LBNP in both High (37.72 ± 0.52°C) and Reduced (37.95 ± 0.54°C) trials (both P < 0.0001). At 60%CSI skin temperature remained elevated in the High trial (37.51 ± 0.56°C) but was reduced to 34.97 ± 0.72°C by the water-perfused suit in the Reduced trial ( P < 0.0001 between trials). Cutaneous vascular conductance was not different between trials [High: 1.57 ± 0.43 vs. Reduced: 1.39 ± 0.38 arbitrary units (AU)/mmHg; P = 0.367] before LBNP but decreased to 0.67 ± 0.19 AU/mmHg at 60%CSI in the Reduced trial while remaining unchanged in the High trial ( P = 0.002 between trials). CSI was higher in the Reduced (695 ± 386 mmHg·min) relative to the High (441 ± 290 mmHg·min; P = 0.023) trial. Mean arterial pressure was not different between trials at presyncope (High: 62 ± 10 vs. Reduced: 62 ± 9 mmHg; P = 0.958). Small reductions in skin temperature after the onset of a simulated hemorrhagic challenge improve LBNP tolerance after exercise heat stress. This may have important implications regarding treatment of an exercise heat-stressed individual (e.g., soldier) who has experienced a hemorrhagic injury.
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Affiliation(s)
- Claire E. Trotter
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - Faith K. Pizzey
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - Philip M. Batterson
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - Robert A. Jacobs
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - James Pearson
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
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Carrara M, Babini G, Baselli G, Ristagno G, Pastorelli R, Brunelli L, Ferrario M. Blood pressure variability, heart functionality, and left ventricular tissue alterations in a protocol of severe hemorrhagic shock and resuscitation. J Appl Physiol (1985) 2018; 125:1011-1020. [PMID: 30001154 PMCID: PMC6230573 DOI: 10.1152/japplphysiol.00348.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Autonomic control of blood pressure (BP) and heart rate (HR) is crucial during bleeding and hemorrhagic shock (HS) to compensate for hypotension and hypoxia. Previous works have observed that at the point of hemodynamic decompensation a marked suppression of BP and HR variability occurs, leading to irreversible shock. We hypothesized that recovery of the autonomic control may be decisive for effective resuscitation, along with restoration of mean BP. We computed cardiovascular indexes of baroreflex sensitivity and BP and HR variability by analyzing hemodynamic recordings collected from five pigs during a protocol of severe hemorrhage and resuscitation; three pigs were sham-treated controls. Moreover, we assessed the effects of severe hemorrhage on heart functionality by integrating the hemodynamic findings with measures of plasma high-sensitivity cardiac troponin T and metabolite concentrations in left ventricular (LV) tissue. Resuscitation was performed with fluids and norepinephrine and then by reinfusion of shed blood. After first resuscitation, mean BP reached the target value, but cardiovascular indexes were not fully restored, hinting at a partial recovery of the autonomic mechanisms. Moreover, cardiac troponins were still elevated, suggesting a persistent myocardial sufferance. After blood reinfusion all the indexes returned to baseline. In the harvested heart, LV metabolic profile confirmed the acute stress condition sensed by the cardiomyocytes. Variability indexes and baroreflex trends can be valuable tools to evaluate the severity of HS, and they may represent a more useful end point for resuscitation in combination with standard measures such as mean values and biological measures. NEW & NOTEWORTHY Autonomic control of blood pressure was highly impaired during hemorrhagic shock, and it was not completely recovered after resuscitation despite global restoration of mean pressures. Moreover, a persistent myocardial sufferance emerged from measured cardiac troponin T and metabolite concentrations of left ventricular tissue. We highlight the importance of combining global mean values and biological markers with measures of variability and autonomic control for a better characterization of the effectiveness of the resuscitation strategy.
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Affiliation(s)
- Marta Carrara
- Department of Electronics, Information, and Bioengineering, Politecnico di Milano, Milan , Italy
| | - Giovanni Babini
- Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy.,Department of Pathophysiology and Transplantation, University of Milan , Milan , Italy
| | - Giuseppe Baselli
- Department of Electronics, Information, and Bioengineering, Politecnico di Milano, Milan , Italy
| | | | | | - Laura Brunelli
- Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy
| | - Manuela Ferrario
- Department of Electronics, Information, and Bioengineering, Politecnico di Milano, Milan , Italy
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John RT, Henricson J, Junker J, Jonson CO, Nilsson GE, Wilhelms D, Anderson CD. A cool response-The influence of ambient temperature on capillary refill time. JOURNAL OF BIOPHOTONICS 2018; 11:e201700371. [PMID: 29384267 DOI: 10.1002/jbio.201700371] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Accepted: 01/21/2018] [Indexed: 06/07/2023]
Abstract
OBJECTIVE To describe the effect of low ambient temperature on skin temperature and capillary refill (CR) time in forehead, sternum and finger pulp. METHODS An observational, nonrandomized experimental study on 15 healthy subjects (6 females) in a cold room (8°C). Outcome measures were skin temperature and quantified CR test after application of a standardized blanching pressure (9 N/cm2 ) using digital photographic polarization spectroscopy to generate CR times. RESULTS The finger pulp showed marked temperature fall and prolonged CR times (>10 seconds). The CR registrations of the forehead and sternum were more comparable to curves observed in a control material at room temperature, and skin temperature falls were less marked. CR times were not prolonged in forehead measurements. At the sternum, some individuals showed CR times beyond guideline recommendations despite only a marginal reduction in skin temperature. CONCLUSIONS Low ambient temperature is a strong independent factor for CR time at peripheral sites. Reservation about sternum as a site of measurement is warranted since cold provocation produced prolonged CR times in some individuals. We found that the forehead is the most thermostable of the 3 sites and thus the preferred site to avoid ambient temperature artifact in measuring CR time.
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Affiliation(s)
- Rani Toll John
- Division of Neuro and Inflammation Sciences, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden
- Department of Emergency Medicine, Local Health Care Services in Central Östergötland, Linköping, Östergötland, Sweden
| | - Joakim Henricson
- Department of Emergency Medicine, Local Health Care Services in Central Östergötland, Linköping, Östergötland, Sweden
- Division of Drug Research, Department of Medical and Health Sciences, Faculty of Health Sciences, Linköping University, Linköping, Sweden
| | - Johan Junker
- Center for Disaster Medicine and Traumatology and Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | - Carl-Oscar Jonson
- Center for Disaster Medicine and Traumatology and Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden
| | | | - Daniel Wilhelms
- Department of Emergency Medicine, Local Health Care Services in Central Östergötland, Linköping, Östergötland, Sweden
- Division of Drug Research, Department of Medical and Health Sciences, Faculty of Health Sciences, Linköping University, Linköping, Sweden
| | - Chris D Anderson
- Division of Cell Biology, Department of Clinical and Experimental Medicine, Faculty of Health Sciences, Linköping University, Linköping, Sweden
- Department of Dermatology and Venereology, Heart and Medicine Center, Linköping, Sweden
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Dziuda Ł, Krej M, Śmietanowski M, Sobotnicki A, Sobiech M, Kwaśny P, Brzozowska A, Baran P, Kowalczuk K, Skibniewski FW. Development and evaluation of a novel system for inducing orthostatic challenge by tilt tests and lower body negative pressure. Sci Rep 2018; 8:7793. [PMID: 29773912 PMCID: PMC5958117 DOI: 10.1038/s41598-018-26173-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 05/08/2018] [Indexed: 01/28/2023] Open
Abstract
Lower body negative pressure (LBNP) is a method derived from space medicine, which in recent years has been increasingly used by clinicians to assess the efficiency of the cardiovascular regulatory mechanisms. LBNP with combined tilt testing is considered as an effective form of training to prevent orthostatic intolerance. We have developed a prototype system comprising a tilt table and LBNP chamber, and tested it in the context of the feasibility of the device for assessing the pilots' efficiency. The table allows for controlled tilting in the range from -45 to +80° at the maximum change rate of 45°/s. The LBNP value can smoothly be adjusted down to -100 mmHg at up to 20 mmHg/s. 17 subjects took part in the pilot study. A 24-minute scenario included -100 mmHg supine LBNP, head up tilt (HUT) and -60 mmHg LBNP associated with HUT, separated by resting phases. The most noticeable changes were observed in stroke volume (SV). During supine LBNP, HUT and the combined stimulus, a decrease of the SV value by 20%, 40% and below 50%, respectively, were detected. The proposed system can map any pre-programed tilt and LBNP profiles, and the pilot study confirmed the efficiency of performing experimental procedures.
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Affiliation(s)
- Łukasz Dziuda
- Department of Flight Simulator Innovations, Military Institute of Aviation Medicine, ul. Krasińskiego 54/56, 01-755, Warszawa, Poland.
| | - Mariusz Krej
- Department of Flight Simulator Innovations, Military Institute of Aviation Medicine, ul. Krasińskiego 54/56, 01-755, Warszawa, Poland
| | - Maciej Śmietanowski
- Department of Experimental and Clinical Physiology, Medical University of Warsaw, ul. Banacha 1B, 02-097, Warszawa, Poland
| | - Aleksander Sobotnicki
- Department of Research and Development, Institute of Medical Technology and Equipment, ul. Roosevelta 118, 41-800, Zabrze, 41-800, Poland
| | - Mariusz Sobiech
- Department of Research and Development, Institute of Medical Technology and Equipment, ul. Roosevelta 118, 41-800, Zabrze, 41-800, Poland
| | - Piotr Kwaśny
- ETC-PZL Aerospace Industries Sp. z o.o., Aleja Krakowska 110/114, 02-256, Warszawa, Poland
| | - Anna Brzozowska
- ETC-PZL Aerospace Industries Sp. z o.o., Aleja Krakowska 110/114, 02-256, Warszawa, Poland
| | - Paulina Baran
- Department of Flight Simulator Innovations, Military Institute of Aviation Medicine, ul. Krasińskiego 54/56, 01-755, Warszawa, Poland
| | - Krzysztof Kowalczuk
- Department of Simulator Studies and Aeromedical Training, Military Institute of Aviation Medicine, ul. Krasińskiego 54/56, 01-755, Warszawa, Poland
| | - Franciszek W Skibniewski
- Department of Flight Simulator Innovations, Military Institute of Aviation Medicine, ul. Krasińskiego 54/56, 01-755, Warszawa, Poland
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Xiang L, Hinojosa-Laborde C, Ryan KL, Rickards CA, Convertino VA. Time course of compensatory physiological responses to central hypovolemia in high- and low-tolerant human subjects. Am J Physiol Regul Integr Comp Physiol 2018; 315:R408-R416. [PMID: 29668322 DOI: 10.1152/ajpregu.00361.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Lower body negative pressure (LBNP) simulates hemorrhage in human subjects. Most subjects (67%) exhibited high tolerance (HT) to hypovolemia, while the remainder (33%) had low tolerance (LT). To investigate the mechanisms for decompensation to central hypovolemia in HT and LT subjects, we characterized the time course of total peripheral resistance (TPR), heart rate (HR), and muscle sympathetic nerve activity (MSNA) during LBNP to tolerance determined by the onset of decompensation (presyncope, PS). We hypothesized that 1) maximum (Max) TPR, HR, and MSNA would coincide, and 2) PS would result from simultaneous decreases in TPR, HR, and MSNA in LT and HT subjects but occur earlier in LT than in HT subjects. Max TPR was lower and occurred earlier in LT ( n = 59) than in HT ( n = 113) subjects (LT: 24 ± 1 mmHg·min·1-1 at 756 ± 31 s; HT: 28 ± 1 mmHg·min·1-1 at 1,265 ± 37 s, P < 0.01). Max TPR occurred several minutes before PS. During subsequent decrease in TPR, HR and MSNA continued to increase. Max HR (LT: 111 ± 2 beat/min at 923 ± 27 s; HT: 130 ± 2 beats/min at 1489 ± 23 s, P < 0.01) occurred several seconds before PS. Higher MSNA ( P < 0.01) was attained in HT ( n = 10; 51 ± 5 bursts/min at max TPR; 54 ± 5 bursts/min at max HR) than LT subjects ( n = 4; 41 ± 8 bursts/min at max TPR; 39 ± 8 bursts/min at max HR). The onset of cardiovascular decompensation is a biphasic process in which vasodilation occurs before bradycardia and sympathetic withdrawal. This pattern was similar in LT and HT but occurred earlier in LT subjects. We conclude that sudden bradycardia plays a critical role in the determination of tolerance to central hypovolemia.
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Affiliation(s)
- Lusha Xiang
- United States Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, San Antonio, Texas
| | - Carmen Hinojosa-Laborde
- United States Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, San Antonio, Texas
| | - Kathy L Ryan
- United States Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, San Antonio, Texas
| | - Caroline A Rickards
- Institute for Cardiovascular and Metabolic Disease, University of North Texas Health Science Center , Fort Worth, Texas
| | - Victor A Convertino
- United States Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, San Antonio, Texas.,United States Army Medical Research and Materiel Command, Fort Detrick, Frederick, Maryland
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Using support vector machines on photoplethysmographic signals to discriminate between hypovolemia and euvolemia. PLoS One 2018; 13:e0195087. [PMID: 29596477 PMCID: PMC5875841 DOI: 10.1371/journal.pone.0195087] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Accepted: 03/18/2018] [Indexed: 11/19/2022] Open
Abstract
Identifying trauma patients at risk of imminent hemorrhagic shock is a challenging task in intraoperative and battlefield settings given the variability of traditional vital signs, such as heart rate and blood pressure, and their inability to detect blood loss at an early stage. To this end, we acquired N = 58 photoplethysmographic (PPG) recordings from both trauma patients with suspected hemorrhage admitted to the hospital, and healthy volunteers subjected to blood withdrawal of 0.9 L. We propose four features to characterize each recording: goodness of fit (r2), the slope of the trend line, percentage change, and the absolute change between amplitude estimates in the heart rate frequency range at the first and last time points. Also, we propose a machine learning algorithm to distinguish between blood loss and no blood loss. The optimal overall accuracy of discriminating between hypovolemia and euvolemia was 88.38%, while sensitivity and specificity were 88.86% and 87.90%, respectively. In addition, the proposed features and algorithm performed well even when moderate blood volume was withdrawn. The results suggest that the proposed features and algorithm are suitable for the automatic discrimination between hypovolemia and euvolemia, and can be beneficial and applicable in both intraoperative/emergency and combat casualty care.
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The Compensatory Reserve For Early and Accurate Prediction Of Hemodynamic Compromise: A Review of the Underlying Physiology. Shock 2018; 45:580-90. [PMID: 26950588 DOI: 10.1097/shk.0000000000000559] [Citation(s) in RCA: 85] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Shock is deadly and unpredictable if it is not recognized and treated in early stages of hemorrhage. Unfortunately, measurements of standard vital signs that are displayed on current medical monitors fail to provide accurate or early indicators of shock because of physiological mechanisms that effectively compensate for blood loss. As a result of new insights provided by the latest research on the physiology of shock using human experimental models of controlled hemorrhage, it is now recognized that measurement of the body's reserve to compensate for reduced circulating blood volume is the single most important indicator for early and accurate assessment of shock. We have called this function the "compensatory reserve," which can be accurately assessed by real-time measurements of changes in the features of the arterial waveform. In this paper, the physiology underlying the development and evaluation of a new noninvasive technology that allows for real-time measurement of the compensatory reserve will be reviewed, with its clinical implications for earlier and more accurate prediction of shock.
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van Helmond N, Johnson BD, Holbein WW, Petersen‐Jones HG, Harvey RE, Ranadive SM, Barnes JN, Curry TB, Convertino VA, Joyner MJ. Effect of acute hypoxemia on cerebral blood flow velocity control during lower body negative pressure. Physiol Rep 2018; 6:e13594. [PMID: 29464923 PMCID: PMC5820424 DOI: 10.14814/phy2.13594] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2017] [Revised: 01/03/2018] [Accepted: 01/05/2018] [Indexed: 11/24/2022] Open
Abstract
The ability to maintain adequate cerebral blood flow and oxygenation determines tolerance to central hypovolemia. We tested the hypothesis that acute hypoxemia during simulated blood loss in humans would cause impairments in cerebral blood flow control. Ten healthy subjects (32 ± 6 years, BMI 27 ± 2 kg·m-2 ) were exposed to stepwise lower body negative pressure (LBNP, 5 min at 0, -15, -30, and -45 mmHg) during both normoxia and hypoxia (Fi O2 = 0.12-0.15 O2 titrated to an SaO2 of ~85%). Physiological responses during both protocols were expressed as absolute changes from baseline, one subject was excluded from analysis due to presyncope during the first stage of LBNP during hypoxia. LBNP induced greater reductions in mean arterial pressure during hypoxia versus normoxia (MAP, at -45 mmHg: -20 ± 3 vs. -5 ± 3 mmHg, P < 0.01). Despite differences in MAP, middle cerebral artery velocity responses (MCAv) were similar between protocols (P = 0.41) due to increased cerebrovascular conductance index (CVCi) during hypoxia (main effect, P = 0.04). Low frequency MAP (at -45 mmHg: 17 ± 5 vs. 0 ± 5 mmHg2 , P = 0.01) and MCAv (at -45 mmHg: 4 ± 2 vs. -1 ± 1 cm·s-2 , P = 0.04) spectral power density, as well as low frequency MAP-mean MCAv transfer function gain (at -30 mmHg: 0.09 ± 0.06 vs. -0.07 ± 0.06 cm·s-1 ·mmHg-1 , P = 0.04) increased more during hypoxia versus normoxia. Contrary to our hypothesis, these findings support the notion that cerebral blood flow control is not impaired during exposure to acute hypoxia and progressive central hypovolemia despite lower MAP as a result of compensated increases in cerebral conductance and flow variability.
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Affiliation(s)
| | - Blair D. Johnson
- Center for Research and Education in Special EnvironmentsDepartment of Exercise and Nutrition SciencesUniversity at BuffaloBuffaloNew York
| | | | | | - Ronée E. Harvey
- Mayo Clinic School of Medicine and ScienceMayo ClinicRochesterMinnesota
| | | | - Jill N. Barnes
- Department of KinesiologyUniversity of Wisconsin‐MadisonMadisonWisconsin
| | | | - Victor A. Convertino
- US Army Battlefield Health & Trauma Center for Human Integrative PhysiologyFort Sam HoustonTexas
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The Effect of Passive Heat Stress and Exercise-Induced Dehydration on the Compensatory Reserve During Simulated Hemorrhage. Shock 2018; 46:74-82. [PMID: 27183303 DOI: 10.1097/shk.0000000000000653] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Compensatory reserve represents the proportion of physiological responses engaged to compensate for reductions in central blood volume before the onset of decompensation. We hypothesized that compensatory reserve would be reduced by hyperthermia and exercise-induced dehydration, conditions often encountered on the battlefield. Twenty healthy males volunteered for two separate protocols during which they underwent lower-body negative pressure (LBNP) to hemodynamic decompensation (systolic blood pressure <80 mm Hg). During protocol #1, LBNP was performed following a passive increase in core temperature of ∼1.2°C (HT) or a normothermic time-control period (NT). During protocol #2, LBNP was performed following exercise during which: fluid losses were replaced (hydrated), fluid intake was restricted and exercise ended at the same increase in core temperature as hydrated (isothermic dehydrated), or fluid intake was restricted and exercise duration was the same as hydrated (time-match dehydrated). Compensatory reserve was estimated with the compensatory reserve index (CRI), a machine-learning algorithm that extracts features from continuous photoplethysmograph signals. Prior to LBNP, CRI was reduced by passive heating [NT: 0.87 (SD 0.09) vs. HT: 0.42 (SD 0.19) units, P <0.01] and exercise-induced dehydration [hydrated: 0.67 (SD 0.19) vs. isothermic dehydrated: 0.52 (SD 0.21) vs. time-match dehydrated: 0.47 (SD 0.25) units; P <0.01 vs. hydrated]. During subsequent LBNP, CRI decreased further and its rate of change was similar between conditions. CRI values at decompensation did not differ between conditions. These results suggest that passive heating and exercise-induced dehydration limit the body's physiological reserve to compensate for further reductions in central blood volume.
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The Compensatory Reserve Index Following Injury: Results of a Prospective Clinical Trial. Shock 2018; 46:61-7. [PMID: 27172155 DOI: 10.1097/shk.0000000000000647] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
INTRODUCTION Humans are able to compensate for significant blood loss with little change in traditional vital signs. We hypothesized that an algorithm, which recognizes compensatory changes in photoplethysmogram (PPG) waveforms, could detect active bleeding and ongoing volume loss in injured patients. METHODS Injured adults were prospectively enrolled at a level I trauma center. PPG data collection was conducted using a custom-made pulse oximeter. Waveform data were post-processed by an algorithm to calculate the compensatory reserve index (CRI), measured on a scale of 1 to 0, with 1 indicating fully compensated and 0 indicating no reserve, or decompensation. CRI was compared to clinical findings. RESULTS Fifty patients were enrolled in the study; 3 had incomplete data, 3 had indeterminate bleeding, 12 were actively bleeding, and 32 were not bleeding. The mean initial CRI of bleeding patients was significantly lower compared with the non-bleeding patients (CRI 0.17, 95% CI = 0.13-0.22 vs. CRI 0.56, 95% CI = 0.49-0.62, P < 0.001). Using a cut-off of 0.21 had a sensitivity of 0.97 and specificity of 0.83 for identifying bleeding patients. CRI had a higher sensitivity than heart rate (75%), systolic blood pressure (63%), shock index (27%), base deficit (29%), lactate (80%), hemoglobin (50%), and hematocrit (50%). During ongoing bleeding, CRI decreased following fluid resuscitation, and conversely increased for patients who were not bleeding. CONCLUSIONS A novel computational algorithm that recognizes subtle changes in PPG waveforms can quickly and noninvasively discern which patients are actively bleeding and continuing to bleed with high sensitivity and specificity in acutely injured patients.
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Abstract
The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.
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Affiliation(s)
- Ivo Torres Filho
- US Army Institute of Surgical Research, JBSA Fort Sam Houston, Texas, USA
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Harris T, Davenport R, Mak M, Brohi K. The Evolving Science of Trauma Resuscitation. Emerg Med Clin North Am 2017; 36:85-106. [PMID: 29132583 DOI: 10.1016/j.emc.2017.08.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This review summarizes the evolution of trauma resuscitation from a one-size-fits-all approach to one tailored to patient physiology. The most dramatic change is in the management of actively bleeding patients, with a balanced blood product-based resuscitation approach (avoiding crystalloids) and surgery focused on hemorrhage control, not definitive care. When hemostasis has been achieved, definitive resuscitation to restore organ perfusion is initiated. This approach is associated with decreased mortality, reduced duration of stay, improved coagulation profile, and reduced crystalloid/vasopressor use. This article focuses on the tools and methods used for trauma resuscitation in the acute phase of trauma care.
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Affiliation(s)
- Tim Harris
- Emergency Medicine, Barts Health NHS Trust, Queen Mary University of London, London, UK
| | - Ross Davenport
- Trauma Sciences, Blizard Institute, Queen Mary University of London, London, UK
| | - Matthew Mak
- Emergency Medicine, Barts Health NHS Trust, London, UK
| | - Karim Brohi
- Trauma and Neuroscience, Blizard Institute, Queen Mary University of London, London E1 2AT, UK; London's Air Ambulance, Barts Health NHS Trust, London, UK.
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77
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Goswami N, Blaber AP, Hinghofer-Szalkay H, Montani JP. Orthostatic Intolerance in Older Persons: Etiology and Countermeasures. Front Physiol 2017; 8:803. [PMID: 29163185 PMCID: PMC5677785 DOI: 10.3389/fphys.2017.00803] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 09/29/2017] [Indexed: 12/16/2022] Open
Abstract
Orthostatic challenge produced by upright posture may lead to syncope if the cardiovascular system is unable to maintain adequate brain perfusion. This review outlines orthostatic intolerance related to the aging process, long-term bedrest confinement, drugs, and disease. Aging-associated illness or injury due to falls often leads to hospitalization. Older patients spend up to 83% of hospital admission lying in bed and thus the consequences of bedrest confinement such as physiological deconditioning, functional decline, and orthostatic intolerance represent a central challenge in the care of the vulnerable older population. This review examines current scientific knowledge regarding orthostatic intolerance and how it comes about and provides a framework for understanding of (patho-) physiological concepts of cardiovascular (in-) stability in ambulatory and bedrest confined senior citizens as well as in individuals with disease conditions [e.g., orthostatic intolerance in patients with diabetes mellitus, multiple sclerosis, Parkinson's, spinal cord injury (SCI)] or those on multiple medications (polypharmacy). Understanding these aspects, along with cardio-postural interactions, is particularly important as blood pressure destabilization leading to orthostatic intolerance affects 3-4% of the general population, and in 4 out of 10 cases the exact cause remains elusive. Reviewed also are countermeasures to orthostatic intolerance such as exercise, water drinking, mental arithmetic, cognitive training, and respiration training in SCI patients. We speculate that optimally applied countermeasures such as mental challenge maintain sympathetic activity, and improve venous return, stroke volume, and consequently, blood pressure during upright standing. Finally, this paper emphasizes the importance of an active life style in old age and why early re-mobilization following bedrest confinement or bedrest is crucial in preventing orthostatic intolerance, falls and falls-related injuries in older persons.
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Affiliation(s)
- Nandu Goswami
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
| | - Andrew P Blaber
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Helmut Hinghofer-Szalkay
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
| | - Jean-Pierre Montani
- Department of Medicine/Physiology, University of Fribourg, Fribourg, Switzerland
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Rahimi M, Blaber AP, Menon C. Motorized adaptive compression system for enhancing venous return: A feasibility study on healthy individuals. Med Eng Phys 2017; 50:65-74. [PMID: 29102275 DOI: 10.1016/j.medengphy.2017.10.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 08/18/2017] [Accepted: 10/04/2017] [Indexed: 10/18/2022]
Abstract
Notwithstanding the extensive use of conventional compression devices in managing venous disorders, these modalities have shortages that diminish their treatment efficacy and lessen patient adherence to therapy. The purpose of this study was to develop an improved compression system that eliminates the flaws of the existing devices. A motorized bandage was designed that takes advantage of continuous feedback from force-sensing resistors to apply reproducible, controlled pressure on the lower extremities. The performance of the device in enhancing venous return was explored in a pilot test on 11 healthy participants, wherein graded lower body negative pressure was employed as a surrogate of passive standing. Each subject underwent two experiments; with and without pressure application over the calves. A two-way repeated-measures analysis of variance revealed a significant difference in the mean hemodynamic responses when the compression bandage was in action (p < .05). Specifically, a meaningful increase was observed in mean arterial pressure by 5%, diastolic blood pressure by 8% and left ventricular ejection time by 4%; and a significant decrease of 5% and 6% was noticed in heart rate and pulse pressure, respectively. These results demonstrate the capability of the designed system in attenuating the imposed orthostatic stress on cardiovascular system.
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Affiliation(s)
- Mahan Rahimi
- MENRVA Research Group, Schools of Mechatronic Systems Engineering and Engineering Science, Simon Fraser University, Metro Vancouver, BC V3T 0A3, Canada
| | - Andrew P Blaber
- Aerospace Physiology Laboratory, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC V5A 1S6, Canada
| | - Carlo Menon
- MENRVA Research Group, Schools of Mechatronic Systems Engineering and Engineering Science, Simon Fraser University, Metro Vancouver, BC V3T 0A3, Canada.
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79
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Verma AK, Xu D, Garg A, Cote AT, Goswami N, Blaber AP, Tavakolian K. Non-linear Heart Rate and Blood Pressure Interaction in Response to Lower-Body Negative Pressure. Front Physiol 2017; 8:767. [PMID: 29114227 PMCID: PMC5660688 DOI: 10.3389/fphys.2017.00767] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 09/20/2017] [Indexed: 12/14/2022] Open
Abstract
Early detection of hemorrhage remains an open problem. In this regard, blood pressure has been an ineffective measure of blood loss due to numerous compensatory mechanisms sustaining arterial blood pressure homeostasis. Here, we investigate the feasibility of causality detection in the heart rate and blood pressure interaction, a closed-loop control system, for early detection of hemorrhage. The hemorrhage was simulated via graded lower-body negative pressure (LBNP) from 0 to -40 mmHg. The research hypothesis was that a significant elevation of causal control in the direction of blood pressure to heart rate (i.e., baroreflex response) is an early indicator of central hypovolemia. Five minutes of continuous blood pressure and electrocardiogram (ECG) signals were acquired simultaneously from young, healthy participants (27 ± 1 years, N = 27) during each LBNP stage, from which heart rate (represented by RR interval), systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) were derived. The heart rate and blood pressure causal interaction (RR↔SBP and RR↔MAP) was studied during the last 3 min of each LBNP stage. At supine rest, the non-baroreflex arm (RR→SBP and RR→MAP) showed a significantly (p < 0.001) higher causal drive toward blood pressure regulation compared to the baroreflex arm (SBP→RR and MAP→RR). In response to moderate category hemorrhage (-30 mmHg LBNP), no change was observed in the traditional marker of blood loss i.e., pulse pressure (p = 0.10) along with the RR→SBP (p = 0.76), RR→MAP (p = 0.60), and SBP→RR (p = 0.07) causality compared to the resting stage. Contrarily, a significant elevation in the MAP→RR (p = 0.004) causality was observed. In accordance with our hypothesis, the outcomes of the research underscored the potential of compensatory baroreflex arm (MAP→RR) of the heart rate and blood pressure interaction toward differentiating a simulated moderate category hemorrhage from the resting stage. Therefore, monitoring baroreflex causality can have a clinical utility in making triage decisions to impede hemorrhage progression.
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Affiliation(s)
- Ajay K Verma
- Department of Electrical Engineering, University of North Dakota, Grand Forks, ND, United States
| | - Da Xu
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Amanmeet Garg
- Department of Engineering Science, Simon Fraser University, Burnaby, BC, Canada
| | - Anita T Cote
- School of Human Kinetics, Trinity Western University, Langley, BC, Canada
| | - Nandu Goswami
- Institute of Physiology, Medical University of Graz, Graz, Austria
| | - Andrew P Blaber
- Department of Electrical Engineering, University of North Dakota, Grand Forks, ND, United States.,Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Kouhyar Tavakolian
- Department of Electrical Engineering, University of North Dakota, Grand Forks, ND, United States.,Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
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Tymko MM, Rickards CA, Skow RJ, Ingram-Cotton NC, Howatt MK, Day TA. The effects of superimposed tilt and lower body negative pressure on anterior and posterior cerebral circulations. Physiol Rep 2017; 4:4/17/e12957. [PMID: 27634108 PMCID: PMC5027361 DOI: 10.14814/phy2.12957] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 08/14/2016] [Indexed: 11/24/2022] Open
Abstract
Steady-state tilt has no effect on cerebrovascular reactivity to increases in the partial pressure of end-tidal carbon dioxide (PETCO2). However, the anterior and posterior cerebral circulations may respond differently to a variety of stimuli that alter central blood volume, including lower body negative pressure (LBNP). Little is known about the superimposed effects of head-up tilt (HUT; decreased central blood volume and intracranial pressure) and head-down tilt (HDT; increased central blood volume and intracranial pressure), and LBNP on cerebral blood flow (CBF) responses. We hypothesized that (a) cerebral blood velocity (CBV; an index of CBF) responses during LBNP would not change with HUT and HDT, and (b) CBV in the anterior cerebral circulation would decrease to a greater extent compared to posterior CBV during LBNP when controlling PETCO2 In 13 male participants, we measured CBV in the anterior (middle cerebral artery, MCAv) and posterior (posterior cerebral artery, PCAv) cerebral circulations using transcranial Doppler ultrasound during LBNP stress (-50 mmHg) in three body positions (45°HUT, supine, 45°HDT). PETCO2 was measured continuously and maintained at constant levels during LBNP through coached breathing. Our main findings were that (a) steady-state tilt had no effect on CBV responses during LBNP in both the MCA (P = 0.077) and PCA (P = 0.583), and (b) despite controlling for PETCO2, both the MCAv and PCAv decreased by the same magnitude during LBNP in HUT (P = 0.348), supine (P = 0.694), and HDT (P = 0.407). Here, we demonstrate that there are no differences in anterior and posterior circulations in response to LBNP in different body positions.
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Affiliation(s)
- Michael M Tymko
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science University of British Columbia, Kelowna, Canada Department of Biology, Faculty of Science and Technology Mount Royal University, Calgary, Alberta, Canada
| | - Caroline A Rickards
- Institute for Cardiovascular & Metabolic Diseases, University of North Texas Health Science Centre, Fort Worth, Texas
| | - Rachel J Skow
- Department of Biology, Faculty of Science and Technology Mount Royal University, Calgary, Alberta, Canada Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Nathan C Ingram-Cotton
- Department of Biology, Faculty of Science and Technology Mount Royal University, Calgary, Alberta, Canada
| | - Michael K Howatt
- Department of Biology, Faculty of Science and Technology Mount Royal University, Calgary, Alberta, Canada
| | - Trevor A Day
- Department of Biology, Faculty of Science and Technology Mount Royal University, Calgary, Alberta, Canada
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81
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Convertino VA, Sawka MN. Wearable technology for compensatory reserve to sense hypovolemia. J Appl Physiol (1985) 2017; 124:442-451. [PMID: 28751369 DOI: 10.1152/japplphysiol.00264.2017] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Traditional monitoring technologies fail to provide accurate or early indications of hypovolemia-mediated extremis because physiological systems (as measured by vital signs) effectively compensate until circulatory failure occurs. Hypovolemia is the most life-threatening physiological condition associated with circulatory shock in hemorrhage or sepsis, and it impairs one's ability to sustain physical exertion during heat stress. This review focuses on the physiology underlying the development of a novel noninvasive wearable technology that allows for real-time evaluation of the cardiovascular system's ability to compensate to hypovolemia, or its compensatory reserve, which provides an individualized estimate of impending circulatory collapse. Compensatory reserve is assessed by real-time changes (sampled millions of times per second) in specific features (hundreds of features) of arterial waveform analog signals that can be obtained from photoplethysmography using machine learning and feature extraction techniques. Extensive experimental evidence employing acute reductions in central blood volume (using lower-body negative pressure, blood withdrawal, heat stress, dehydration) demonstrate that compensatory reserve provides the best indicator for early and accurate assessment for compromises in blood pressure, tissue perfusion, and oxygenation in resting human subjects. Engineering challenges exist for the development of a ruggedized wearable system that can measure signals from multiple sites, improve signal-to-noise ratios, be customized for use in austere conditions (e.g., battlefield, patient transport), and be worn during strenuous physical activity.
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Affiliation(s)
- Victor A Convertino
- Battlefield Health & Trauma Center for Human Integrative Physiology, U. S. Army Institute of Surgical Research, Joint Base San Antonio-Fort Sam Houston, San Antonio, Texas
| | - Michael N Sawka
- School of Biological Sciences, Georgia Institute of Technology , Atlanta, Georgia
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84
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Kay VL, Sprick JD, Rickards CA. Cerebral oxygenation and regional cerebral perfusion responses with resistance breathing during central hypovolemia. Am J Physiol Regul Integr Comp Physiol 2017; 313:R132-R139. [PMID: 28539354 DOI: 10.1152/ajpregu.00385.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Revised: 04/21/2017] [Accepted: 05/11/2017] [Indexed: 11/22/2022]
Abstract
Resistance breathing improves tolerance to central hypovolemia induced by lower body negative pressure (LBNP), but this is not related to protection of anterior cerebral blood flow [indexed by mean middle cerebral artery velocity (MCAv)]. We hypothesized that inspiratory resistance breathing improves tolerance to central hypovolemia by maintaining cerebral oxygenation (ScO2), and protecting cerebral blood flow in the posterior cerebral circulation [indexed by posterior cerebral artery velocity (PCAv)]. Eight subjects (4 male/4 female) completed two experimental sessions of a presyncopal-limited LBNP protocol (3 mmHg/min onset rate) with and without (Control) resistance breathing via an impedance threshold device (ITD). ScO2 (via near-infrared spectroscopy), MCAv and PCAv (both via transcranial Doppler ultrasound), and arterial pressure (via finger photoplethysmography) were measured continuously. Hemodynamic responses were analyzed between the Control and ITD condition at baseline (T1) and the time representing 10 s before presyncope in the Control condition (T2). While breathing on the ITD increased LBNP tolerance from 1,506 ± 75 s to 1,704 ± 88 s (P = 0.003), both mean MCAv and mean PCAv were similar between conditions at T2 (P ≥ 0.46), and decreased by the same magnitude with and without ITD breathing (P ≥ 0.53). ScO2 also decreased by ~9% with or without ITD breathing at T2 (P = 0.97), and there were also no differences in deoxygenated (dHb) or oxygenated hemoglobin (HbO2) between conditions at T2 (P ≥ 0.43). There was no evidence that protection of regional cerebral blood velocity (i.e., anterior or posterior cerebral circulation) nor cerebral oxygen extraction played a key role in the determination of tolerance to central hypovolemia with resistance breathing.
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Affiliation(s)
- Victoria L Kay
- Institute for Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, Texas
| | - Justin D Sprick
- Institute for Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, Texas
| | - Caroline A Rickards
- Institute for Cardiovascular and Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, Texas
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Rodriguez J, Blaber AP, Kneihsl M, Trozic I, Ruedl R, Green DA, Broadbent J, Xu D, Rössler A, Hinghofer-Szalkay H, Fazekas F, Goswami N. Poststroke alterations in heart rate variability during orthostatic challenge. Medicine (Baltimore) 2017; 96:e5989. [PMID: 28383399 PMCID: PMC5411183 DOI: 10.1097/md.0000000000005989] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Older adults following recovery from ischemic stroke have a higher incidence of orthostatic hypotension, syncope, and fall risk, which may be related to impaired autonomic responses limiting the ability to maintain cerebral blood flow. Thus, we investigated cerebrovascular and cardiovascular regulation in 23 adults ≥55 years of age, 10 diagnosed with ischemic stroke, and 13 age-matched healthy controls when sitting at rest and upon standing to compare differences of autonomic variables at ∼7 months (218 ± 41 days) poststroke.Arterial blood pressure via finger plethysmography, muscle-pump baroreflex via electromyography, heart rate variability via 3-lead ECG, and cerebral blood flow velocity via transcranial Doppler were analyzed while sitting for 5 minutes and then during quiet standing for 5 minutes.From the seated to standing position, the stroke group had significantly greater decline in the low frequency component of heart rate variability (164 [79] vs 25 [162] ms; P = 0.043). All other cardiovascular parameters and assessments of autonomic function were not significantly different between the two groups.Our findings support the hypothesis of continued autonomic dysfunction after recovery from ischemic stroke, with potential attenuation of the cardiovascular response to standing. However, further investigation is required to determine the mechanisms underlying the increased risk of orthostatic hypotension, syncope, and falls poststroke.
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Affiliation(s)
- Joel Rodriguez
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
- Centre of Human and Aerospace Physiological Sciences, King's College London, London, UK
| | - Andrew Philip Blaber
- Aerospace Physiology Laboratory, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Markus Kneihsl
- Department of Neurology, Medical University of Graz, Graz, Austria
| | - Irhad Trozic
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
| | - Rebecca Ruedl
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
| | - David A. Green
- Centre of Human and Aerospace Physiological Sciences (CHAPS), King's College London, Faculty of Life Sciences and Medicine, Guy's Campus, London, UK
- KBRwyle, European Astronaut Centre, Linder Höhe, Cologne, Germany
| | - James Broadbent
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
- Centre of Human and Aerospace Physiological Sciences, King's College London, London, UK
| | - Da Xu
- Aerospace Physiology Laboratory, Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
| | - Andreas Rössler
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
| | - Helmut Hinghofer-Szalkay
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
| | - Franz Fazekas
- Department of Neurology, Medical University of Graz, Graz, Austria
| | - Nandu Goswami
- Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz, Graz, Austria
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Tymko MM. How to build a lower-body differential pressure chamber integrated on a tilt-table: A pedagogy tool to demonstrate the cardiovagal baroreflex. Facets (Ott) 2017. [DOI: 10.1139/facets-2016-0012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The cardiovagal baroreflex is an important physiological reflex that is commonly taught in health-related university physiology courses. This reflex is responsible for the rapid maintenance of blood pressure through dynamic changes in heart rate (HR) and vascular resistance. The use of lower-body negative pressure (LBNP) and lower-body positive pressure (LBPP) can manipulate these stretch sensitive baroreceptors. High performance and relatively inexpensive homemade LBNP and LBPP chambers can be easily constructed providing a valuable tool for both research and teaching purposes. There has been previous documentation of how to build a LBNP chamber; however, the information available usually lacks appropriate construction details, and there is currently no literature on how to build a chamber that can accommodate both LBNP and LBPP. In addition, a recently developed novel LBNP/LBPP chamber positioned on a 360° tilt-table provided the unique utility of superimposing both LBNP/LBPP and body position as independent or combined stressors to alter central blood volume. The primary purposes of this manuscript are to (1) provide step-by-step instructions on how to build a tilt-table LBNP/LBPP chamber, and (2) demonstrate the effectiveness of a tilt-table LBNP/LBPP chamber to facilitate undergraduate and graduate learning in the laboratory by effectively demonstrating the cardiovagal baroreflex.
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Affiliation(s)
- Michael M. Tymko
- Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Science, Faculty of Health and Social Development, University of British Columbia, 3333 University Way, Kelowna, BC V1V 1V7, Canada
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Walz JM, Stundner O, Girardi FP, Barton BA, Koll-Desrosiers AR, Heard SO, Memtsoudis SG. Microvascular response to transfusion in elective spine surgery. World J Orthop 2017; 8:49-56. [PMID: 28144579 PMCID: PMC5241545 DOI: 10.5312/wjo.v8.i1.49] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Revised: 08/19/2016] [Accepted: 10/27/2016] [Indexed: 02/06/2023] Open
Abstract
AIM To investigate the microvascular (skeletal muscle tissue oxygenation; SmO2) response to transfusion in patients undergoing elective complex spine surgery.
METHODS After IRB approval and written informed consent, 20 patients aged 18 to 85 years of age undergoing > 3 level anterior and posterior spine fusion surgery were enrolled in the study. Patients were followed throughout the operative procedure, and for 12 h postoperatively. In addition to standard American Society of Anesthesiologists monitors, invasive measurements including central venous pressure, continual analysis of stroke volume (SV), cardiac output (CO), cardiac index (CI), and stroke volume variability (SVV) was performed. To measure skeletal muscle oxygen saturation (SmO2) during the study period, a non-invasive adhesive skin sensor based on Near Infrared Spectroscopy was placed over the deltoid muscle for continuous recording of optical spectra. All administration of fluids and blood products followed standard procedures at the Hospital for Special Surgery, without deviation from usual standards of care at the discretion of the Attending Anesthesiologist based on individual patient comorbidities, hemodynamic status, and laboratory data. Time stamps were collected for administration of colloids and blood products, to allow for analysis of SmO2 immediately before, during, and after administration of these fluids, and to allow for analysis of hemodynamic data around the same time points. Hemodynamic and oxygenation variables were collected continuously throughout the surgery, including heart rate, blood pressure, mean arterial pressure, SV, CO, CI, SVV, and SmO2. Bivariate analyses were conducted to examine the potential associations between the outcome of interest, SmO2, and each hemodynamic parameter measured using Pearson’s correlation coefficient, both for the overall cohort and within-patients individually. The association between receipt of packed red blood cells and SmO2 was performed by running an interrupted time series model, with SmO2 as our outcome, controlling for the amount of time spent in surgery before and after receipt of PRBC and for the inherent correlation between observations. Our model was fit using PROC AUTOREG in SAS version 9.2. All other analyses were also conducted in SAS version 9.2 (SAS Institute Inc., Cary, NC, United States).
RESULTS Pearson correlation coefficients varied widely between SmO2 and each hemodynamic parameter examined. The strongest positive correlations existed between ScvO2 (P = 0.41) and SV (P = 0.31) and SmO2; the strongest negative correlations were seen between albumin (P = -0.43) and cell saver (P = -0.37) and SmO2. Correlations for other laboratory parameters studied were weak and only based on a few observations. In the final model we found a small, but significant increase in SmO2 at the time of PRBC administration by 1.29 units (P = 0.0002). SmO2 values did not change over time prior to PRBC administration (P = 0.6658) but following PRBC administration, SmO2 values declined significantly by 0.015 units (P < 0.0001).
CONCLUSION Intra-operative measurement of SmO2 during large volume, yet controlled hemorrhage, does not show a statistically significant correlation with either invasive hemodynamic, or laboratory parameters in patients undergoing elective complex spine surgery.
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88
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Convertino VA, Hinojosa-Laborde C, Muniz GW, Carter R. Integrated Compensatory Responses in a Human Model of Hemorrhage. J Vis Exp 2016. [PMID: 27911370 DOI: 10.3791/54737] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Hemorrhage is the leading cause of trauma-related deaths, partly because early diagnosis of the severity of blood loss is difficult. Assessment of hemorrhaging patients is difficult because current clinical tools provide measures of vital signs that remain stable during the early stages of bleeding due to compensatory mechanisms. Consequently, there is a need to understand and measure the total integration of mechanisms that compensate for reduced circulating blood volume and how they change during ongoing progressive hemorrhage. The body's reserve to compensate for reduced circulating blood volume is called the 'compensatory reserve'. The compensatory reserve can be accurately evaluated with real-time measurements of changes in the features of the arterial waveform measured with the use of a high-powered computer. Lower Body Negative Pressure (LBNP) has been shown to simulate many of the physiological responses in humans associated with hemorrhage, and is used to study the compensatory response to hemorrhage. The purpose of this study is to demonstrate how compensatory reserve is assessed during progressive reductions in central blood volume with LBNP as a simulation of hemorrhage.
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Affiliation(s)
- Victor A Convertino
- U.S. Army Institute of Surgical Research, JBSA Fort Sam Houston; U.S. Army Medical Research and Materiel Command, JBSA Fort Sam Houston;
| | - Carmen Hinojosa-Laborde
- Tactical Combat Casualty Care Research, JBSA Fort Sam Houston; U.S. Army Institute of Surgical Research, JBSA Fort Sam Houston
| | - Gary W Muniz
- Tactical Combat Casualty Care Research, JBSA Fort Sam Houston; U.S. Army Institute of Surgical Research, JBSA Fort Sam Houston
| | - Robert Carter
- Tactical Combat Casualty Care Research, JBSA Fort Sam Houston; U.S. Army Institute of Surgical Research, JBSA Fort Sam Houston
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Skytioti M, Søvik S, Elstad M. Internal carotid artery blood flow in healthy awake subjects is reduced by simulated hypovolemia and noninvasive mechanical ventilation. Physiol Rep 2016; 4:e12969. [PMID: 27702883 PMCID: PMC5064133 DOI: 10.14814/phy2.12969] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 08/20/2016] [Accepted: 08/22/2016] [Indexed: 02/02/2023] Open
Abstract
Intact cerebral blood flow (CBF) is essential for cerebral metabolism and function, whereas hypoperfusion in relation to hypovolemia and hypocapnia can lead to severe cerebral damage. This study was designed to assess internal carotid artery blood flow (ICA-BF) during simulated hypovolemia and noninvasive positive pressure ventilation (PPV) in young healthy humans. Beat-by-beat blood velocity (ICA and aorta) were measured by Doppler ultrasound during normovolemia and simulated hypovolemia (lower body negative pressure), with or without PPV in 15 awake subjects. Heart rate, plethysmographic finger arterial pressure, respiratory frequency, and end-tidal CO2 (ETCO2) were also recorded. Cardiac index (CI) and ICA-BF were calculated beat-by-beat. Medians and 95% confidence intervals and Wilcoxon signed rank test for paired samples were used to test the difference between conditions. Effects on ICA-BF were modeled by linear mixed-effects regression analysis. During spontaneous breathing, ICA-BF was reduced from normovolemia (247, 202-284 mL/min) to hypovolemia (218, 194-271 mL/min). During combined PPV and hypovolemia, ICA-BF decreased by 15% (200, 152-231 mL/min, P = 0.001). Regression analysis attributed this fall to concurrent reductions in CI (β: 43.2, SE: 17.1, P = 0.013) and ETCO2 (β: 32.8, SE: 9.3, P = 0.001). Mean arterial pressure was maintained and did not contribute to ICA-BF variance. In healthy awake subjects, ICA-BF was significantly reduced during simulated hypovolemia combined with noninvasive PPV Reductions in CI and ETCO2 had additive effects on ICA-BF reduction. In hypovolemic patients, even low-pressure noninvasive ventilation may cause clinically relevant reductions in CBF, despite maintained arterial blood pressure.
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Affiliation(s)
- Maria Skytioti
- Division of Physiology, Institute of Basic Medical Sciences University of Oslo, Oslo, Norway
| | - Signe Søvik
- Deptartment of Anaesthesia and Intensive Care, Akershus University Hospital, Lørenskog, Norway
| | - Maja Elstad
- Division of Physiology, Institute of Basic Medical Sciences University of Oslo, Oslo, Norway
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90
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van Helmond N, Johnson BD, Curry TB, Cap AP, Convertino VA, Joyner MJ. White blood cell concentrations during lower body negative pressure and blood loss in humans. Exp Physiol 2016; 101:1265-1275. [DOI: 10.1113/ep085952] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2016] [Accepted: 08/11/2016] [Indexed: 11/08/2022]
Affiliation(s)
| | - Blair D. Johnson
- Department of Anesthesiology; Mayo Clinic; Rochester MN USA
- Center for Research and Education in Special Environments; Department of Exercise and Nutrition Sciences; University at Buffalo; Buffalo NY USA
| | | | - Andrew P. Cap
- US Army Institute of Surgical Research; Fort Sam Houston; TX USA
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91
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Cardiac stroke volume variability measured non-invasively by three methods for detection of central hypovolemia in healthy humans. Eur J Appl Physiol 2016; 116:2187-2196. [DOI: 10.1007/s00421-016-3471-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Accepted: 09/05/2016] [Indexed: 10/21/2022]
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92
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Specificity of Compensatory Reserve and Tissue Oxygenation as Early Predictors of Tolerance to Progressive Reductions in Central Blood Volume. Shock 2016; 46:68-73. [DOI: 10.1097/shk.0000000000000632] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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93
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Laurin A, Khosrow-Khavar F, Blaber AP, Tavakolian K. Accurate and consistent automatic seismocardiogram annotation without concurrent ECG. Physiol Meas 2016; 37:1588-604. [PMID: 27510446 DOI: 10.1088/0967-3334/37/9/1588] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Seismocardiography (SCG) is the measurement of vibrations in the sternum caused by the beating of the heart. Precise cardiac mechanical timings that are easily obtained from SCG are critically dependent on accurate identification of fiducial points. So far, SCG annotation has relied on concurrent ECG measurements. An algorithm capable of annotating SCG without the use any other concurrent measurement was designed. We subjected 18 participants to graded lower body negative pressure. We collected ECG and SCG, obtained R peaks from the former, and annotated the latter by hand, using these identified peaks. We also annotated the SCG automatically. We compared the isovolumic moment timings obtained by hand to those obtained using our algorithm. Mean ± confidence interval of the percentage of accurately annotated cardiac cycles were [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for levels of negative pressure 0, -20, -30, -40, and -50 mmHg. LF/HF ratios, the relative power of low-frequency variations to high-frequency variations in heart beat intervals, obtained from isovolumic moments were also compared to those obtained from R peaks. The mean differences ± confidence interval were [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for increasing levels of negative pressure. The accuracy and consistency of the algorithm enables the use of SCG as a stand-alone heart monitoring tool in healthy individuals at rest, and could serve as a basis for an eventual application in pathological cases.
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Affiliation(s)
- A Laurin
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, University Dr, Burnaby, BC, V5A 1S6, Canada. Inria Saclay Ile-de-France, Rue Honoré d'Estienne d'Orves, Palaiseau, 91120, France
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94
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Yadav K, Singh A, Jaryal AK, Coshic P, Chatterjee K, Deepak KK. Modulation of cardiac autonomic tone in non-hypotensive hypovolemia during blood donation. J Clin Monit Comput 2016; 31:739-746. [PMID: 27484693 DOI: 10.1007/s10877-016-9912-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 07/25/2016] [Indexed: 11/25/2022]
Abstract
Non-hypotensive hypovolemia, observed during mild haemorrhage or blood donation leads to reflex readjustment of the cardiac autonomic tone. In the present study, the cardiac autonomic tone was quantified using heart rate and blood pressure variability during and after non-hypotensive hypovolemia of blood donation. 86 voluntary healthy male blood donors were recruited for the study (age 35 ± 9 years; weight 78 ± 12 kg; height 174 ± 6 cms). Continuous lead II ECG and beat-to-beat blood pressure was recorded before, during and after blood donation followed by offline time and frequency domain analysis of HRV and BPV. The overall heart rate variability (SDNN and total power) did not change during or after blood donation. However, there was a decrease in indices that represent the parasympathetic component (pNN50 %, SDSD and HF) while an increase was observed in sympathetic component (LF) along with an increase in sympathovagal balance (LF:HF ratio) during blood donation. These changes were sustained for the period immediately following blood donation. No fall of blood pressure was observed during the period of study. The blood pressure variability showed an increase in the SDNN, CoV and RMSSD time domain measures in the post donation period. These results suggest that mild hypovolemia produced by blood donation is non-hypotensive but is associated with significant changes in the autonomic tone. The increased blood pressure variability and heart rate changes that are seen only in the later part of donation period could be because of the progressive hypovolemia associated parasympathetic withdrawal and sympathetic activation that manifest during the course of blood donation.
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Affiliation(s)
- Kavita Yadav
- Department of Physiology, All India Institute of Medical Sciences, Room No. 2009, Teaching Block, Second Floor, Ansari Nagar, New Delhi, India
| | - Akanksha Singh
- Department of Physiology, All India Institute of Medical Sciences, Room No. 2009, Teaching Block, Second Floor, Ansari Nagar, New Delhi, India
| | - Ashok Kumar Jaryal
- Department of Physiology, All India Institute of Medical Sciences, Room No. 2009, Teaching Block, Second Floor, Ansari Nagar, New Delhi, India.
| | - Poonam Coshic
- Transfusion Medicine (Blood Bank), All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - Kabita Chatterjee
- Transfusion Medicine (Blood Bank), All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India
| | - K K Deepak
- Department of Physiology, All India Institute of Medical Sciences, Room No. 2009, Teaching Block, Second Floor, Ansari Nagar, New Delhi, India
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95
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Shivkumar K, Ajijola OA, Anand I, Armour JA, Chen PS, Esler M, De Ferrari GM, Fishbein MC, Goldberger JJ, Harper RM, Joyner MJ, Khalsa SS, Kumar R, Lane R, Mahajan A, Po S, Schwartz PJ, Somers VK, Valderrabano M, Vaseghi M, Zipes DP. Clinical neurocardiology defining the value of neuroscience-based cardiovascular therapeutics. J Physiol 2016; 594:3911-54. [PMID: 27114333 PMCID: PMC4945719 DOI: 10.1113/jp271870] [Citation(s) in RCA: 212] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2016] [Accepted: 04/08/2016] [Indexed: 12/13/2022] Open
Abstract
The autonomic nervous system regulates all aspects of normal cardiac function, and is recognized to play a critical role in the pathophysiology of many cardiovascular diseases. As such, the value of neuroscience-based cardiovascular therapeutics is increasingly evident. This White Paper reviews the current state of understanding of human cardiac neuroanatomy, neurophysiology, pathophysiology in specific disease conditions, autonomic testing, risk stratification, and neuromodulatory strategies to mitigate the progression of cardiovascular diseases.
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Affiliation(s)
- Kalyanam Shivkumar
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Center of Excellence, Los Angeles, CA, USA
| | - Olujimi A Ajijola
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Center of Excellence, Los Angeles, CA, USA
| | - Inder Anand
- Department of Cardiology, University of Minnesota Medical School, Minneapolis, MN, USA
| | - J Andrew Armour
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Center of Excellence, Los Angeles, CA, USA
| | - Peng-Sheng Chen
- Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Murray Esler
- Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
| | | | - Michael C Fishbein
- Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, California, USA
| | - Jeffrey J Goldberger
- Division of Cardiology, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Ronald M Harper
- Department of Neurobiology and the Brain Research Institute, University of California, Los Angeles, CA, USA
| | - Michael J Joyner
- Division of Cardiovascular Diseases, Mayo Clinic and Mayo Foundation, Rochester, MN, USA
| | | | - Rajesh Kumar
- Departments of Anesthesiology and Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Richard Lane
- Department of Psychiatry, University of Arizona College of Medicine, Tucson, AZ, USA
| | - Aman Mahajan
- Department of Anesthesia, UCLA, Los Angeles, CA, USA
| | - Sunny Po
- Heart Rhythm Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK, USA
- University of Tulsa Oxley College of Health Sciences, Tulsa, OK, USA
| | - Peter J Schwartz
- Center for Cardiac Arrhythmias of Genetic Origin, IRCCS Instituto Auxologico Italiano, c/o Centro Diagnostico e di Ricerrca San Carlo, Milan, Italy
| | - Virend K Somers
- Division of Cardiovascular Diseases, Mayo Clinic and Mayo Foundation, Rochester, MN, USA
| | - Miguel Valderrabano
- Methodist DeBakey Heart and Vascular Center and Methodist Hospital Research Institute, Houston Methodist Hospital, Houston, TX, USA
| | - Marmar Vaseghi
- UCLA Cardiac Arrhythmia Center and Neurocardiology Research Center of Excellence, Los Angeles, CA, USA
| | - Douglas P Zipes
- Indiana University School of Medicine, Indianapolis, IN, USA
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96
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Bronzwaer ASGT, Verbree J, Stok WJ, van Buchem MA, Daemen MJAP, van Osch MJP, van Lieshout JJ. Cardiovascular Response Patterns to Sympathetic Stimulation by Central Hypovolemia. Front Physiol 2016; 7:235. [PMID: 27378944 PMCID: PMC4913112 DOI: 10.3389/fphys.2016.00235] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2016] [Accepted: 05/30/2016] [Indexed: 11/30/2022] Open
Abstract
In healthy subjects, variation in cardiovascular responses to sympathetic stimulation evoked by submaximal lower body negative pressure (LBNP) is considerable. This study addressed the question whether inter-subject variation in cardiovascular responses coincides with consistent and reproducible responses in an individual subject. In 10 healthy subjects (5 female, median age 22 years), continuous hemodynamic parameters (finger plethysmography; Nexfin, Edwards Lifesciences), and time-domain baroreflex sensitivity (BRS) were quantified during three consecutive 5-min runs of LBNP at −50 mmHg. The protocol was repeated after 1 week to establish intra-subject reproducibility. In response to LBNP, 5 subjects (3 females) showed a prominent increase in heart rate (HR; 54 ± 14%, p = 0.001) with no change in total peripheral resistance (TPR; p = 0.25) whereas the other 5 subjects (2 females) demonstrated a significant rise in TPR (7 ± 3%, p = 0.017) with a moderate increase in HR (21 ± 9%, p = 0.004). These different reflex responses coincided with differences in resting BRS (22 ± 8 vs. 11 ± 3 ms/mmHg, p = 0.049) and resting HR (57 ± 8 vs. 71 ± 12 bpm, p = 0.047) and were highly reproducible over time. In conclusion, we found distinct cardiovascular response patterns to sympathetic stimulation by LBNP in young healthy individuals. These patterns of preferential autonomic blood pressure control appeared related to resting cardiac BRS and HR and were consistent over time.
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Affiliation(s)
- Anne-Sophie G T Bronzwaer
- Department of Internal Medicine, Academic Medical Center, University of AmsterdamAmsterdam, Netherlands; Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical CenterAmsterdam, Netherlands
| | - Jasper Verbree
- Department of Radiology, Leiden University Medical Center Leiden, Netherlands
| | - Wim J Stok
- Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical CenterAmsterdam, Netherlands; Department of Anatomy, Embryology and Physiology, Academic Medical Center, University of AmsterdamAmsterdam, Netherlands
| | - Mark A van Buchem
- Department of Radiology, Leiden University Medical Center Leiden, Netherlands
| | - Mat J A P Daemen
- Department of Pathology, Academic Medical Center, University of Amsterdam Amsterdam, Netherlands
| | | | - Johannes J van Lieshout
- Department of Internal Medicine, Academic Medical Center, University of AmsterdamAmsterdam, Netherlands; Laboratory for Clinical Cardiovascular Physiology, Center for Heart Failure Research, Academic Medical CenterAmsterdam, Netherlands; MRC/Arthritis Research UK Centre for Musculoskeletal Ageing Research, School of Life Sciences, University of Nottingham Medical School, Queen's Medical CentreNottingham, UK
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97
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Rimehaug AE, Hoff IE, Høiseth LØ, Hisdal J, Aadahl P, Kirkeby-Garstad I. Cardiac power parameters during hypovolemia, induced by the lower body negative pressure technique, in healthy volunteers. BMC Anesthesiol 2016; 16:31. [PMID: 27364749 PMCID: PMC4929737 DOI: 10.1186/s12871-016-0195-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2015] [Accepted: 05/13/2016] [Indexed: 02/02/2023] Open
Abstract
Background Changes in cardiac power parameters incorporate changes in both aortic flow and blood pressure. We hypothesized that dynamic and non-dynamic cardiac power parameters would track hypovolemia better than equivalent flow- and pressure parameters, both during spontaneous breathing and non-invasive positive pressure ventilation (NPPV). Methods Fourteen healthy volunteers underwent lower body negative pressure (LBNP) of 0, −20, −40, −60 and −80 mmHg to simulate hypovolemia, both during spontaneous breathing and during NPPV. We recorded aortic flow using suprasternal ultrasound Doppler and blood pressure using Finometer, and calculated dynamic and non-dynamic parameters of cardiac power, flow and blood pressure. These were assessed on their association with LBNP-levels. Results Respiratory variation in peak aortic flow was the dynamic parameter most affected during spontaneous breathing increasing 103 % (p < 0.001) from baseline to LBNP −80 mmHg. Respiratory variation in pulse pressure was the most affected dynamic parameter during NPPV, increasing 119 % (p < 0.001) from baseline to LBNP −80 mmHg. The cardiac power integral was the most affected non-dynamic parameter falling 59 % (p < 0.001) from baseline to LBNP −80 mmHg during spontaneous breathing, and 68 % (p < 0.001) during NPPV. Conclusions Dynamic cardiac power parameters were not better than dynamic flow- and pressure parameters at tracking hypovolemia, seemingly due to previously unknown variation in peripheral vascular resistance matching respiratory changes in hemodynamics. Of non-dynamic parameters, the power parameters track hypovolemia slightly better than equivalent flow parameters, and far better than equivalent pressure parameters.
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Affiliation(s)
- Audun Eskeland Rimehaug
- Department of Anesthesiology and Intensive care, St Olav Trondheim University Hospital, Trondheim, Norway. .,Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway. .,Circulation research group Trondheim (CIRCUT), Trondheim, Norway.
| | - Ingrid Elise Hoff
- Norwegian Air Ambulance Foundation, Drøbak, Norway.,Department of Anesthesiology, Oslo University Hospital, Oslo, Norway
| | - Lars Øivind Høiseth
- Department of Anesthesiology, Oslo University Hospital, Oslo, Norway.,Faculty of Medicine, University of Oslo, Oslo, Norway
| | - Jonny Hisdal
- Department of Vascular Medicine, Oslo University Hospital, Oslo, Norway
| | - Petter Aadahl
- Department of Anesthesiology and Intensive care, St Olav Trondheim University Hospital, Trondheim, Norway.,Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway.,Circulation research group Trondheim (CIRCUT), Trondheim, Norway
| | - Idar Kirkeby-Garstad
- Department of Anesthesiology and Intensive care, St Olav Trondheim University Hospital, Trondheim, Norway.,Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway.,Circulation research group Trondheim (CIRCUT), Trondheim, Norway
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98
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Hemodynamic Stability to Surface Warming and Cooling During Sustained and Continuous Simulated Hemorrhage in Humans. Shock 2016; 46:42-9. [PMID: 27224744 DOI: 10.1097/shk.0000000000000661] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
One in 10 deaths worldwide is caused by traumatic injury, and 30% to 40% of those trauma-related deaths are due to hemorrhage. Currently, warming a bleeding victim is the standard of care due to the adverse effects of combined hemorrhage and hypothermia on survival. We tested the hypothesis that heating is detrimental to the maintenance of arterial pressure and cerebral perfusion during hemorrhage, while cooling is beneficial to victims who are otherwise normothermic. Twenty-one men (31 ± 9 y) were examined under two separate protocols designed to produce central hypovolemia similar to hemorrhage. Following 15 min of supine rest, 10 min of 30 mm Hg of lower body negative pressure (LBNP) was applied. On separate randomized days, subjects were then exposed to skin surface cooling (COOL), warming (WARM), or remained thermoneutral (NEUT), while LBNP continued. Subjects remained in these thermal conditions for either 40 min of 30 mm Hg LBNP (N = 9), or underwent a continuous LBNP ramp until hemodynamic decompensation (N = 12). Arterial blood pressure during LBNP was dependent on the thermal perturbation as blood pressure was greater during COOL (P >0.001) relative to NEUT and WARM for both protocols. Middle cerebral artery blood velocity decreased (P <0.001) from baseline throughout sustained and continuous LBNP, but the magnitude of reduction did not differ between thermal conditions. Contrary to our hypothesis, WARM did not reduce cerebral blood velocity or LBNP tolerance relative to COOL and NEUT in normothermic individuals. While COOL increased blood pressure, cerebral perfusion and time to presyncope were not different relative to NEUT or WARM during sustained or continuous LBNP. Warming an otherwise normothermic hemorrhaging victim is not detrimental to hemodynamic stability, nor is this stability improved with cooling.
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99
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Williams AM, Shave RE, Stembridge M, Eves ND. Females have greater left ventricular twist mechanics than males during acute reductions to preload. Am J Physiol Heart Circ Physiol 2016; 311:H76-84. [PMID: 27199112 DOI: 10.1152/ajpheart.00057.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Accepted: 05/09/2016] [Indexed: 11/22/2022]
Abstract
Compared to males, females have smaller left ventricular (LV) dimensions and volumes, higher ejection fractions (EF), and higher LV longitudinal and circumferential strain. LV twist mechanics determine ventricular function and are preload-dependent. Therefore, the sex differences in LV structure and myocardial function may result in different mechanics when preload is altered. This study investigated sex differences in LV mechanics during acute challenges to preload. With the use of conventional and speckle-tracking echocardiography, LV structure and function were assessed in 20 males (24 ± 6.2 yr) and 20 females (23 ± 3.1 yr) at baseline and during progressive levels of lower body negative pressure (LBNP). Fourteen participants (8 males, 6 females) were also assessed following a rapid infusion of saline. LV end-diastolic volume, end-systolic volume, stroke volume (SV), and EF were reduced in both groups during LBNP (P < 0.001). While males had greater absolute volumes (P < 0.001), there were no sex differences in allometrically scaled volumes at any stage. Sex differences were not detected at baseline in basal rotation, apical rotation, or twist. Apical rotation and twist increased in both groups (P < 0.001) with LBNP. At -60 mmHg, females had greater apical rotation (P = 0.009), twist (P = 0.008), and torsion (P = 0.002) and faster untwisting velocity (P = 0.02) than males. There were no differences in mechanics following saline infusion. Females have larger LV twist and a faster untwisting velocity than males during large reductions to preload, supporting that females have a greater reliance on LV twist mechanics to maintain SV during severe reductions to preload.
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Affiliation(s)
- Alexandra M Williams
- Centre for Heart, Lung and Vascular Health, Faculty of Health and Social Development, The University of British Columbia, Kelowna, Canada; and
| | - Rob E Shave
- Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Mike Stembridge
- Centre for Heart, Lung and Vascular Health, Faculty of Health and Social Development, The University of British Columbia, Kelowna, Canada; and Cardiff School of Sport, Cardiff Metropolitan University, Cardiff, United Kingdom
| | - Neil D Eves
- Centre for Heart, Lung and Vascular Health, Faculty of Health and Social Development, The University of British Columbia, Kelowna, Canada; and
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100
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Hinojosa-Laborde C, Howard JT, Mulligan J, Grudic GZ, Convertino VA. Comparison of compensatory reserve during lower-body negative pressure and hemorrhage in nonhuman primates. Am J Physiol Regul Integr Comp Physiol 2016; 310:R1154-9. [PMID: 27030667 DOI: 10.1152/ajpregu.00304.2015] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Accepted: 03/14/2016] [Indexed: 11/22/2022]
Abstract
Compensatory reserve was measured in baboons (n = 13) during hemorrhage (Hem) and lower-body negative pressure (LBNP) using a machine-learning algorithm developed to estimate compensatory reserve by detecting reductions in central blood volume during LBNP. The algorithm calculates compensatory reserve index (CRI) from normovolemia (CRI = 1) to cardiovascular decompensation (CRI = 0). The hypothesis was that Hem and LBNP will elicit similar CRI values and that CRI would have higher specificity than stroke volume (SV) in predicting decompensation. Blood was removed in four steps: 6.25%, 12.5%, 18.75%, and 25% of total blood volume. Four weeks after Hem, the same animals were subjected to four levels of LBNP that was matched on the basis of their central venous pressure. Data (mean ± 95% confidence interval) indicate that CRI decreased (P < 0.001) from baseline during Hem (0.69 ± 0.10, 0.57 ± 0.09, 0.36 ± 0.10, 0.16 ± 0.08, and 0.08 ± 0.03) and LBNP (0.76 ± 0.05, 0.66 ± 0.08, 0.36 ± 0.13, 0.23 ± 0.11, and 0.14 ± 0.09). CRI was not different between Hem and LBNP (P = 0.20). Linear regression analysis between Hem CRI and LBNP CRI revealed a slope of 1.03 and a correlation coefficient of 0.96. CRI exhibited greater specificity than SV in both Hem (92.3 vs. 82.1) and LBNP (94.8 vs. 83.1) and greater ROC AUC in Hem (0.94 vs. 0.84) and LBNP (0.94 vs. 0.92). These data support the hypothesis that Hem and LBNP elicited the same CRI response, suggesting that measurement of compensatory reserve is superior to SV as a predictor of cardiovascular decompensation.
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Affiliation(s)
- Carmen Hinojosa-Laborde
- U.S. Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, Texas; and
| | - Jeffrey T Howard
- U.S. Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, Texas; and
| | | | | | - Victor A Convertino
- U.S. Army Institute of Surgical Research, Joint Base San Antonio Fort Sam Houston, Texas; and
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