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Rosenberg AJ, Anderson GK, McKeefer HJ, Bird J, Pentz B, Byman BRM, Jendzjowsky N, Wilson RJ, Day TA, Rickards CA. Hemorrhage at high altitude: impact of sustained hypobaric hypoxia on cerebral blood flow, tissue oxygenation, and tolerance to simulated hemorrhage in humans. Eur J Appl Physiol 2024:10.1007/s00421-024-05450-1. [PMID: 38489034 DOI: 10.1007/s00421-024-05450-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2023] [Accepted: 02/22/2024] [Indexed: 03/17/2024]
Abstract
With ascent to high altitude (HA), compensatory increases in cerebral blood flow and oxygen delivery must occur to preserve cerebral metabolism and consciousness. We hypothesized that this compensation in cerebral blood flow and oxygen delivery preserves tolerance to simulated hemorrhage (via lower body negative pressure, LBNP), such that tolerance is similar during sustained exposure to HA vs. low altitude (LA). Healthy humans (4F/4 M) participated in LBNP protocols to presyncope at LA (1130 m) and 5-7 days following ascent to HA (3800 m). Internal carotid artery (ICA) blood flow, cerebral delivery of oxygen (CDO2) through the ICA, and cerebral tissue oxygen saturation (ScO2) were determined. LBNP tolerance was similar between conditions (LA: 1276 ± 304 s vs. HA: 1208 ± 306 s; P = 0.58). Overall, ICA blood flow and CDO2 were elevated at HA vs. LA (P ≤ 0.01) and decreased with LBNP under both conditions (P < 0.0001), but there was no effect of altitude on ScO2 responses (P = 0.59). Thus, sustained exposure to hypobaric hypoxia did not negatively impact tolerance to simulated hemorrhage. These data demonstrate the robustness of compensatory physiological mechanisms that preserve human cerebral blood flow and oxygen delivery during sustained hypoxia, ensuring cerebral tissue metabolism and neuronal function is maintained.
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Affiliation(s)
- Alexander J Rosenberg
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
- Integrative Physiology Laboratory, Department of Kinesiology and Nutrition, University of Illinois at Chicago, Chicago, IL, USA
- Physiology Department, Midwestern University, Downers Grove, IL, USA
| | - Garen K Anderson
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | - Haley J McKeefer
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA
| | | | | | | | - Nicholas Jendzjowsky
- University of Calgary, Calgary, AB, Canada
- Institute of Respiratory Medicine & Exercise Physiology, The Lundquist Institute at UCLA Harbor Medical, Torrance, CA, USA
| | | | | | - Caroline A Rickards
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, TX, USA.
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Eid AM, Elgamal M, Gonzalez-Fiol A, Shelley KH, Wu HT, Alian AA. Using the ear photoplethysmographic waveform as an early indicator of central hypovolemia in healthy volunteers utilizing LBNP induced hypovolemia model. Physiol Meas 2023. [PMID: 37116503 DOI: 10.1088/1361-6579/acd165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
OBJECTIVE To study the photoplethysmographic (PPG) waveforms of different locations (ear and finger) during lower body negative pressure (LBNP) induced hypovolemia. Then, to determine whether the PPG waveform can be used to detect hypovolemia during the early stage of LBNP.
Approach: 36 healthy volunteers were recruited for progressive LBNP induced hypovolemia, with an endpoint of -60 mmHg or development of hypoperfusion symptoms, whichever comes first. Subjects tolerating the entire protocol without symptoms were designated as high tolerance (HT), while symptomatic subjects were designated as low tolerance (LT). Subjects were monitored with an electrocardiogram, continuous noninvasive blood pressure monitor (CNAP), and two pulse oximetry probes, one on the ear (Xhale) and one the finger (Nellcor). Stroke volume (SV) was measured non-invasively utilizing NICOM (Cheetah Medical). The waveform morphology was analyzed using novel PPG waveforms indices, including phase hemodynamic index (PHI) and amplitude hemodyamaic index (AHI) and were evaluated from the ear PPG and finger PPG at different LBNP stages.
Main Results: The PHI, particularly the phase relationship between the second harmonic and the fundamental component of the ear PPG denoted as 〖∇φ〗_2, during the early stage of LBNP (-15 mmHg) in the HT and LT groups is statistically significantly different (p value=0.0033) with the area under curve 0.81 (CI: 0.616-0.926). The other indices are not significantly different. The 5 fold cross validation shows that 〖∇φ〗_2 during the early stage of LBNP (-15 mmHg) as the single index could predict the tolerance of the subject with the sensitivity, specificity, accuracy and F1 as 0.771±0.192, 0.71±0.107, 0.7±0.1 and 0.771±0.192 respectively.
Significance: The ear's PPG PHI which compares the phases of the fundamental and second harmonic has the potential to be used as an early predictor of central hypovolemia. 
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Affiliation(s)
- Anna-Maria Eid
- Vanderbilt University Medical Center, 300 11th Avenue North Nashville, TN 37203, Nashville, Tennessee, 37232-2102, UNITED STATES
| | - Mohamed Elgamal
- Saint Mary's Hospital, 56 Franklin St Waterbury, CT 06706, Streator, Illinois, 61364-3399, UNITED STATES
| | - Antonio Gonzalez-Fiol
- Department of Anesthesiology, Yale School of Medicine, 333 Cedar Street, PO Box 208051, New Haven, Connecticut, 06520-8055, UNITED STATES
| | - Kirk H Shelley
- Department of Anesthesiology, Yale School of Medicine, 333 Cedar Street, PO Box 208051, New Haven, Connecticut, 06520-8055, UNITED STATES
| | - Hau-Tieng Wu
- Duke University Department of Mathematics, 120 Science Dr., Durham, North Carolina, 27708-0320, UNITED STATES
| | - Aymen Awad Alian
- Department of Anesthesiology, Yale School of Medicine, 333 Cedar Street, PO Box 208051, New Haven, Connecticut 06520-8051, USA, New Haven, Connecticut, 06520-8055, UNITED STATES
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Mijacika T, Kyhl K, Frestad D, Otto Barak F, Drvis I, Secher NH, Dujic Z, Lav Madsen P. Effect of pulmonary hyperinflation on central blood volume: An MRI study. Respir Physiol Neurobiol 2017; 243:92-96. [PMID: 28583413 DOI: 10.1016/j.resp.2017.05.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 05/31/2017] [Indexed: 11/25/2022]
Abstract
Pulmonary hyperinflation attained by glossopharyngeal insufflation (GPI) challenges the circulation by compressing the heart and pulmonary vasculature. Our aim was to determine the amount of blood translocated from the central blood volume during GPI. Cardiac output and cardiac chamber volumes were assessed by magnetic resonance imaging in twelve breath-hold divers at rest and during apnea with GPI. Pulmonary blood volume was determined from pulmonary blood flow and transit times for gadolinium during first-pass perfusion after intravenous injection. During GPI, the lung volume increased by 0.8±0.6L (11±7%) above the total lung capacity. All cardiac chambers decreased in volume and despite a heart rate increase of 24±29 bpm (39±50%), pulmonary blood flow decreased by 2783±1820mL (43±20%). The pulmonary transit time remained unchanged at 7.5±2.2s and pulmonary blood volume decreased by 354±176mL (47±15%). In total, central blood volume decreased by 532±248mL (46±14%). Voluntary pulmonary hyperinflation leads to ∼50% decrease in pulmonary and central blood volume.
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Affiliation(s)
- Tanja Mijacika
- Dept. of Integrative Physiology, University of Split School of Medicine, Croatia
| | - Kasper Kyhl
- The Cardiac MRI group, Dept. Cardiology, Rigshospitalet, University of Copenhagen, Denmark
| | - Daria Frestad
- Dept. of Cardiology, Copenhagen University Hospital, Hvidovre, University of Copenhagen, Denmark
| | - F Otto Barak
- Dept. of Integrative Physiology, University of Split School of Medicine, Croatia; Dept. of Physiology, Faculty of Medicine, University of Novi Sad, Serbia
| | - Ivan Drvis
- University of Zagreb Faculty of Kinesiology, Croatia
| | - Niels H Secher
- Dept. of Anesthesiology, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Denmark
| | - Zeljko Dujic
- Dept. of Integrative Physiology, University of Split School of Medicine, Croatia.
| | - Per Lav Madsen
- Dept. of Cardiology, Copenhagen University Hospital, Herlev, University of Copenhagen, Denmark
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Abstract
Central hypovolemia elicited by application of lower body negative pressure (LBNP) has been used extensively to simulate hemorrhage in human subjects. Traditional LBNP protocols incorporate progressive steps in pressure held for specific time intervals. The aim of this study was to assess the reproducibility of applying continuous LBNP at a constant rate until presyncope to replicate actual bleeding. During two trials (≥4 weeks intervening), LBNP was applied at a rate of 3 mmHg/min in 18 healthy human subjects (12M; 6F) until the onset of presyncopal symptoms. Heart rate (HR), mean arterial pressure (MAP), stroke volume (SV), total peripheral resistance (TPR), mean middle and posterior cerebral artery velocities (MCAv, PCAv), and cerebral oxygen saturation (ScO2) were measured continuously. Time to presyncope (TTPS) and hemodynamic responses were compared between the two trials. TTPS (1649 ± 98 sec vs. 1690 ± 88 sec; P = 0.47 [t-test]; r = 0.77) and the subsequent magnitude of central hypovolemia (%Δ SV −54 ± 4% vs. −53 ± 4%; P = 0.55) were similar between trials. There were no statistically distinguishable differences at either baseline (P ≥ 0.17) or presyncope between trials for HR, MAP, TPR, mean MCAv, mean PCAv, or ScO2 (P ≥ 0.19). The rate of change from baseline to presyncope for all hemodynamic responses was also similar between trials (P ≥ 0.12). Continuous LBNP applied at a rate of 3 mmHg/min was reproducible in healthy human subjects, eliciting similar reductions in central blood volume and subsequent reflex hemodynamic responses.
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Affiliation(s)
- Victoria L Kay
- Institute for Cardiovascular & Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, Texas
| | - Caroline A Rickards
- Institute for Cardiovascular & Metabolic Diseases, University of North Texas Health Science Center, Fort Worth, Texas
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Yanagida R, Ogawa Y, Ueda K, Aoki K, Iwasaki KI. Sustained mild hypergravity reduces spontaneous cardiac baroreflex sensitivity. Auton Neurosci 2014; 185:123-8. [PMID: 25156804 DOI: 10.1016/j.autneu.2014.07.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Revised: 07/07/2014] [Accepted: 07/08/2014] [Indexed: 10/24/2022]
Abstract
Head-to-foot gravitational force >1G (+Gz hypergravity) augments venous pooling in the lower body and reduces central blood volume during exposure, compared with 1Gz. Central hypovolemia has been reported to reduce spontaneous cardiac baroreflex sensitivity. However, no investigations have examined spontaneous cardiac baroreflex sensitivity during exposure to sustained mild +Gz hypergravity. We therefore hypothesized that mild +Gz hypergravity would reduce spontaneous cardiac baroreflex sensitivity, compared with 1Gz. To test this hypothesis, we examined spontaneous cardiac baroreflex sensitivity in 16 healthy men during exposure to mild +Gz hypergravity using a short-arm centrifuge. Beat-to-beat arterial blood pressure (tonometry) and R-R interval (electrocardiography) were obtained during 1Gz and 1.5Gz exposures. Spontaneous cardiac baroreflex sensitivity was assessed by sequence slope and transfer function gain. Stroke volume was calculated from the arterial pressure waveform using a three-element model. All indices of spontaneous cardiac baroreflex sensitivity decreased significantly (up slope: 18.6±2.3→12.7±1.6ms/mmHg, P<0.001; down slope: 19.0±2.5→13.2±1.3ms/mmHg, P=0.002; transfer function gain in low frequency: 14.4±2.2→10.1±1.1ms/mmHg, P=0.004; transfer function gain in high frequency: 22.2±7.5→12.4±3.5ms/mmHg, P<0.001). Stroke volume decreased significantly (88±5→80±6ml, P=0.025). Moreover, although systolic arterial pressure variability increased, R-R interval variability did not increase. These results suggest that even mild +Gz hypergravity reduces spontaneous cardiac baroreflex sensitivity, increasing the risk of cardiovascular disturbance during the exposure.
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Affiliation(s)
- Ryo Yanagida
- Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan
| | - Yojiro Ogawa
- Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan
| | - Kaname Ueda
- Department of Anesthesiology, Nihon University School of Medicine, Tokyo, Japan
| | - Ken Aoki
- Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan
| | - Ken-ichi Iwasaki
- Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
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