1
|
Coupal KE, Heeney ND, Hockin BCD, Ronsley R, Armstrong K, Sanatani S, Claydon VE. Pubertal Hormonal Changes and the Autonomic Nervous System: Potential Role in Pediatric Orthostatic Intolerance. Front Neurosci 2019; 13:1197. [PMID: 31798399 PMCID: PMC6861527 DOI: 10.3389/fnins.2019.01197] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Accepted: 10/22/2019] [Indexed: 12/22/2022] Open
Abstract
Puberty is initiated by hormonal changes in the adolescent body that trigger physical and behavioral changes to reach adult maturation. As these changes occur, some adolescents experience concerning pubertal symptoms that are associated with dysfunction of the autonomic nervous system (ANS). Vasovagal syncope (VVS) and Postural Orthostatic Tachycardia Syndrome (POTS) are common disorders of the ANS associated with puberty that are related to orthostatic intolerance and share similar symptoms. Compared to young males, young females have decreased orthostatic tolerance and a higher incidence of VVS and POTS. As puberty is linked to changes in specific sex and non-sex hormones, and hormonal therapy sometimes improves orthostatic symptoms in female VVS patients, it is possible that pubertal hormones play a role in the increased susceptibility of young females to autonomic dysfunction. The purpose of this paper is to review the key hormonal changes associated with female puberty, their effects on the ANS, and their potential role in predisposing some adolescent females to cardiovascular autonomic dysfunctions such as VVS and POTS. Increases in pubertal hormones such as estrogen, thyroid hormones, growth hormone, insulin, and insulin-like growth factor-1 promote vasodilatation and decrease blood volume. This may be exacerbated by higher levels of progesterone, which suppresses catecholamine secretion and sympathetic outflow. Abnormal heart rate increases in POTS patients may be exacerbated by pubertal increases in leptin, insulin, and thyroid hormones acting to increase sympathetic nervous system activity and/or catecholamine levels. Given the coincidental timing of female pubertal hormone surges and adolescent onset of VVS and POTS in young women, coupled with the known roles of these hormones in modulating cardiovascular homeostasis, it is likely that female pubertal hormones play a role in predisposing females to VVS and POTS during puberty. Further research is necessary to confirm the effects of female pubertal hormones on autonomic function, and their role in pubertal autonomic disorders such as VVS and POTS, in order to inform the treatment and management of these debilitating disorders.
Collapse
Affiliation(s)
- Kassandra E Coupal
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Natalie D Heeney
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Brooke C D Hockin
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - Rebecca Ronsley
- Department of Pediatrics, BC Children's Hospital, Vancouver, BC, Canada
| | - Kathryn Armstrong
- Children's Heart Centre, BC Children's Hospital, Vancouver, BC, Canada
| | | | - Victoria E Claydon
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| |
Collapse
|
2
|
Ogoh S, Tarumi T. Cerebral blood flow regulation and cognitive function: a role of arterial baroreflex function. J Physiol Sci 2019; 69:813-823. [PMID: 31444691 PMCID: PMC10717347 DOI: 10.1007/s12576-019-00704-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 08/13/2019] [Indexed: 10/26/2022]
Abstract
A strict adequate perfusion pressure via arterial baroreflex for the delivery of oxygen to the tissues of the body is well established; however, the importance of baroreflex for cerebral blood flow (CBF) is unclear. On the other hand, there is convincing evidence for arterial baroreflex function playing an important role in maintaining brain homeostasis, e.g., cerebral metabolism, cerebral hemodynamics, and cognitive function. For example, mild cognitive impairment attenuates the sensitivity of baroreflex, and Alzheimer's disease further decreases it. These clinical findings suggest that CBF and cerebral function are affected by systemic blood pressure regulation via the arterial baroreflex. However, dysfunction of arterial baroreflex is likely to affect CBF regulation as well as the underlying neuronal function, but identifying how this is achieved is arduous since neurological diseases affect systemic as well as cerebral circulation independently. Recent insights into the influence of blood pressure regulation via the arterial baroreflex on cerebral function and blood flow regulation may help elucidate this important question. This review summarizes some update findings regarding direct (autonomic regulation) and indirect (systemic blood pressure regulation) contributions of the arterial baroreflex to the maintenance of cerebral vasculature regulation.
Collapse
Affiliation(s)
- Shigehiko Ogoh
- Department of Biomedical Engineering, Toyo University, 2100 Kujirai, Kawagoe, Saitama, 350-8585, Japan.
| | - Takashi Tarumi
- Human Informatics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan
| |
Collapse
|
3
|
Stewart JM, Pianosi P, Shaban MA, Terilli C, Svistunova M, Visintainer P, Medow MS. Postural Hyperventilation as a Cause of Postural Tachycardia Syndrome: Increased Systemic Vascular Resistance and Decreased Cardiac Output When Upright in All Postural Tachycardia Syndrome Variants. J Am Heart Assoc 2018; 7:e008854. [PMID: 29960989 PMCID: PMC6064900 DOI: 10.1161/jaha.118.008854] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Accepted: 06/07/2018] [Indexed: 12/15/2022]
Abstract
BACKGROUND Postural tachycardia syndrome (POTS) is a heterogeneous condition. We stratified patients previously evaluated for POTS on the basis of supine resting cardiac output (CO) or with the complaint of platypnea or "shortness of breath" during orthostasis. We hypothesize that postural hyperventilation is one cause of POTS and that hyperventilation-associated POTS occurs when initial reduction in CO is sufficiently large. We also propose that circulatory abnormalities normalize with restoration of CO2. METHODS AND RESULTS Fifty-eight enrollees with POTS were compared with 16 healthy volunteer controls. Low CO in POTS was defined by a resting supine CO <4 L/min. Patients with shortness of breath had hyperventilation with end tidal CO2 <30 Torr during head-up tilt table testing. There were no differences in height or weight between control patients and patients with POTS or differences between the POTS groups. Beat-to-beat blood pressure was measured by photoplethysmography, and CO was measured by ModelFlow. Systemic vascular resistance was defined as mean arterial blood pressure/CO. End tidal CO2 and cerebral blood flow velocity of the middle cerebral artery were only reduced during head-up tilt in the hyperventilation group, whereas blood pressure was increased compared with control. We corrected the reduced end tidal CO2 in hyperventilation by addition of exogenous CO2 into a rebreathing apparatus. With added CO2, heart rate, blood pressure, CO, and systemic vascular resistance in hyperventilation became similar to control. CONCLUSIONS We conclude that all POTS is related to decreased CO, decreased central blood volume, and increased systemic vascular resistance and that a variant of POTS is consequent to postural hyperventilation.
Collapse
Affiliation(s)
- Julian M Stewart
- Department of Pediatrics, New York Medical College, Valhalla, NY
- Department of Physiology, New York Medical College, Valhalla, NY
| | - Paul Pianosi
- Paediatric Respiratory Medicine, King's College Hospital National Health Service Foundation Trust, London, United Kingdom
| | - Mohamed A Shaban
- Department of Pediatrics, New York Medical College, Valhalla, NY
| | - Courtney Terilli
- Department of Pediatrics, New York Medical College, Valhalla, NY
| | - Maria Svistunova
- Department of Pediatrics, New York Medical College, Valhalla, NY
| | - Paul Visintainer
- Epidemiology and Biostatistics, Baystate Medical Center, University of Massachusetts School of Medicine, Worcester, MA
| | - Marvin S Medow
- Department of Pediatrics, New York Medical College, Valhalla, NY
- Department of Physiology, New York Medical College, Valhalla, NY
| |
Collapse
|
4
|
Jardine DL, Wieling W, Brignole M, Lenders JWM, Sutton R, Stewart J. The pathophysiology of the vasovagal response. Heart Rhythm 2017; 15:921-929. [PMID: 29246828 DOI: 10.1016/j.hrthm.2017.12.013] [Citation(s) in RCA: 87] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Indexed: 10/18/2022]
Abstract
In part I of this study, we found that the classical studies on vasovagal syncope, conducted in fit young subjects, overstated vasodilatation as the dominant hypotensive mechanism. Since 1980, blood pressure and cardiac output have been measured continuously using noninvasive methods during tilt, mainly in patients with recurrent syncope, including women and the elderly. This has allowed us to analyze in more detail the complex sequence of hemodynamic changes leading up to syncope in the laboratory. All tilt-sensitive patients appear to progress through 4 phases: (1) early stabilization, (2) circulatory instability, (3) terminal hypotension, and (4) recovery. The physiology responsible for each phase is discussed. Although the order of phases is consistent, the time spent in each phase may vary. In teenagers and young adults, progressive hypotension during phases 2 and 3 can be driven by vasodilatation or falling cardiac output. The fall in cardiac output is secondary to a progressive decrease in stroke volume because blood is pooled in the splanchnic veins. In adults a fall in cardiac output is the dominant hypotensive mechanism because systemic vascular resistance always remains above baseline levels.
Collapse
Affiliation(s)
- David L Jardine
- Department of General Medicine, Christchurch Hospital, University of Otago, Christchurch, New Zealand.
| | - Wouter Wieling
- Department of Internal Medicine, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands
| | - Michele Brignole
- Department of Cardiology, Arrhythmologic Centre, Ospedali del Tigullio, Lavagna, Italy
| | - Jacques W M Lenders
- Department of Internal Medicine, Radboud University Medical Centre, Nijmegen, The Netherlands; Department of Internal Medicine III, Technical University Dresden, Dresden, Germany
| | - Richard Sutton
- National Heart and Lung institute, Imperial College, London, United Kingdom
| | - Julian Stewart
- Departments of Pediatrics, Physiology, and Medicine, New York Medical College, Valhalla, New York
| |
Collapse
|
5
|
Castro P, Freitas J, Santos R, Panerai R, Azevedo E. Indexes of cerebral autoregulation do not reflect impairment in syncope: insights from head-up tilt test of vasovagal and autonomic failure subjects. Eur J Appl Physiol 2017; 117:1817-1831. [PMID: 28681121 DOI: 10.1007/s00421-017-3674-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Accepted: 06/26/2017] [Indexed: 12/27/2022]
Abstract
PURPOSE The study of dynamic cerebral autoregulation (CA), which adapts cerebral blood flow to arterial blood pressure (ABP) fluctuations, has been limited in orthostatic intolerance syndromes, mainly due to its stationary prerequisites hardly to meet during maneuvers to provoke syncope itself. New techniques of continuous estimates of CA could overcome this pitfall. We aimed to evaluate CA during head-up tilt test in common conditions causing syncope. METHODS We compared three groups: eight controls; eight patients with autonomic failure due to familial amyloidotic polyneuropathy; eight patients with vasovagal syncope (VVS). ABP and cerebral blood flow velocity (CBFV) were measured with Finometer® and transcranial Doppler. We calculated cerebrovascular resistance index (CVRi), critical closing pressure (CrCP) and resistance area product (RAP), and derived CA continuously from autoregulation index [ARI(t)]. RESULTS With HUTT, AF subjects showed a pronounced decrease in CBFV (-36 ± 17 versus -7 ± 6%, p < 0.0001), ABP (-29 ± 27 versus 7 ± 12%, p < 0.0001) and RAP (-17 ± 23 versus 3 ± 18%, p < 0.0001) but not CVRi (p = 0.110). VVS subjects showed progressive cerebral vasoconstriction prior to syncope, (reduced CBFV 19 ± 15 versus 1 ± 6, p < 0.000; increased RAP 12 ± 18 versus 2 ± 3%, p = 0.024 and CVRi 12 ± 18 versus 2 ± 3%, p = 0.005). ARI(t) increased significantly in AF patients (5.7 ± 1.2 versus 6.9 ± 1.2, p = 0.040) and VVS (5.8 ± 1.2 versus 7.3 ± 1.2, p = 0.015) in response to ABP fall during syncope. CONCLUSIONS Our data suggest that dynamic cerebral autoregulatory response to orthostatic challenge is neither affected by autonomic dysfunction nor in neutrally mediated syncope. This study also emphasizes that RAP + CrCP model is more informative than CVRi, mainly during cerebral vasodilatory response to orthostatic hypotension.
Collapse
Affiliation(s)
- Pedro Castro
- Department of Neurology, São João Hospital Center, Faculty of Medicine of University of Porto, Alameda Professor Hernani Monteiro, 4200-319, Porto, Portugal.
| | - João Freitas
- Autonomic Unit, São João Hospital Center, Faculty of Medicine of University of Porto, Porto, Portugal
| | - Rosa Santos
- Department of Neurology, São João Hospital Center, Faculty of Medicine of University of Porto, Alameda Professor Hernani Monteiro, 4200-319, Porto, Portugal
| | - Ronney Panerai
- Department of Cardiovascular Sciences and NIH Biomedical Research Centre, University of Leicester, Leicester, UK
| | - Elsa Azevedo
- Department of Neurology, São João Hospital Center, Faculty of Medicine of University of Porto, Alameda Professor Hernani Monteiro, 4200-319, Porto, Portugal
| |
Collapse
|
6
|
Harrison JM, Gilchrist PT, Corovic TS, Bogetti C, Song Y, Bacon SL, Ditto B. Respiratory and hemodynamic contributions to emotion-related pre-syncopal vasovagal symptoms. Biol Psychol 2017; 127:46-52. [PMID: 28456564 DOI: 10.1016/j.biopsycho.2017.04.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2015] [Revised: 04/10/2017] [Accepted: 04/22/2017] [Indexed: 02/05/2023]
Abstract
Vasovagal reactions are conventionally understood as resulting from systemic changes in cardiovascular activity; however, there exists a complementary perspective focused on specific changes in cerebral vasoconstriction associated with hyperventilation-induced hypocapnia. The present study investigated the role of cardiovascular and respiratory activity in self-reported pre-syncopal vasovagal reactions to a surgery video in a sample of 49 healthy women. Participants who indicated more previous real-life episodes of dizziness reported experiencing significantly more symptoms in the laboratory consistent with a vasovagal response. They also showed lower total peripheral resistance and higher pre-ejection period in general, suggesting lower sympathetic nervous system activity. Significant decreases in end-tidal carbon dioxide (PETCO2) occurred during the surgery video among susceptible participants, without significant increases in respiration rate. Further, participants who experienced reductions from the neutral video in PETCO2, systolic blood pressure, or both, reported vasovagal symptoms during the surgery video. The results suggest that patterns of respiration associated with decreases in PETCO2 may contribute to vasovagal symptoms reported in non-clinical groups as well as those with blood-injection-injury phobia and are associated with susceptibility to dizziness.
Collapse
Affiliation(s)
- Johanna M Harrison
- Laboratory for Cardiovascular Psychophysiology, Department of Psychology, McGill University, 1205 Ave. Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada.
| | - Philippe T Gilchrist
- Wolfson College, University of Cambridge, Cambridge CB3 9BB, United Kingdom; MRC/BHF Cardiovascular Epidemiology Unit, Department of Public Health and Primary Care, University of Cambridge, Strangeways Research Laboratory, 2 Wort's Causeway, Cambridge, CB1 8RN, United Kingdom
| | - Tiana S Corovic
- Laboratory for Cardiovascular Psychophysiology, Department of Psychology, McGill University, 1205 Ave. Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada
| | - Curtis Bogetti
- Laboratory for Cardiovascular Psychophysiology, Department of Psychology, McGill University, 1205 Ave. Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada
| | - Yuqing Song
- Laboratory for Cardiovascular Psychophysiology, Department of Psychology, McGill University, 1205 Ave. Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada
| | - Simon L Bacon
- Department of Exercise Science, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec, H4 B 1R6, Canada
| | - Blaine Ditto
- Laboratory for Cardiovascular Psychophysiology, Department of Psychology, McGill University, 1205 Ave. Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada
| |
Collapse
|
7
|
Cerebral oximetry with blood volume index and capnography in intubated and hyperventilated patients. Am J Emerg Med 2016; 34:1102-7. [DOI: 10.1016/j.ajem.2016.03.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Revised: 02/29/2016] [Accepted: 03/01/2016] [Indexed: 11/21/2022] Open
|
8
|
Disgust stimuli reduce heart rate but do not contribute to vasovagal symptoms. J Behav Ther Exp Psychiatry 2016; 51:116-22. [PMID: 26851836 DOI: 10.1016/j.jbtep.2016.01.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Revised: 12/09/2015] [Accepted: 01/27/2016] [Indexed: 11/23/2022]
Abstract
BACKGROUND AND OBJECTIVES The vasovagal response demonstrates a unique form of stress response, common in medical settings yet provoked by a variety of blood-injury-injection stimuli. This study aimed to better understand the psychophysiological mechanisms of the vasovagal response.. METHODS 16 undergraduates with and 42 without a self-reported history of fainting watched five 3-5 min videos with different emotional content. One documentary clip (Neutral condition) described a campus environmental project while another (Blood/Injury) depicted portions of an open heart surgery. Three additional clips were also used, including Medical, Threat, and Contamination stimuli. Vasovagal symptoms and physiological variables were assessed during each video. RESULTS As predicted, while the disgust-related stimuli (Blood/Injury, Medical, Contamination) were associated with generally lower heart rate, the Blood/Injury video produced the highest symptoms and the only significant difference between previous fainters and non-fainters. The physiological measures also revealed that participants with a fainting history experienced higher stroke volume and lower systolic blood pressure throughout, as well as several main effects of video. LIMITATIONS An additional decrease in systolic blood pressure and respiration produced by watching the Blood/Injury video may have been sufficient to trigger symptoms in some, though results also suggest that systemic variables do not entirely explain susceptibility to symptoms. More careful evaluation of regional blood flow may be required. CONCLUSIONS Participants who had previously experienced strong vasovagal responses displayed what appeared to be an anticipatory response to the Blood/Injury video. Finally, disgust stimuli may reduce heart rate but do not appear to contribute to vasovagal symptoms.
Collapse
|
9
|
Habek M, Krbot Skorić M, Crnošija L, Adamec I. Brainstem dysfunction protects against syncope in multiple sclerosis. J Neurol Sci 2015; 357:69-74. [PMID: 26145199 DOI: 10.1016/j.jns.2015.06.066] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Revised: 06/27/2015] [Accepted: 06/29/2015] [Indexed: 10/23/2022]
Abstract
BACKGROUND The aim of this study was to investigate the correlation between autonomic dysfunction in multiple sclerosis (MS) and brainstem dysfunction evaluated with the vestibular evoked myogenic potentials (VEMP) score and conventional MRI. METHODS Forty-five patients with the diagnosis of clinically isolated syndrome (CIS) suggestive of MS were enrolled. VEMP, heart rate, and blood pressure responses to the Valsalva maneuver, heart rate response to deep breathing, and pain provoked head-up tilt table test, as well as brain and spinal cord MRI were performed. RESULTS There was no difference in the VEMP score between patients with and without signs of sympathetic or parasympathetic dysfunction. However, patients with syncope had significantly lower VEMP score compared to patients without syncope (p<0.01). Patients with orthostatic hypotension (OH) showed a trend of higher VEMP score compared to patients without OH (p=0.06). There was no difference in the presence of lesions in the brainstem or cervical spinal cord between patients with or without any of the studied autonomic parameters. The model consisting of a VEMP score of ≤5 and normal MRI of the midbrain and cervical spinal cord has sensitivity and specificity of 83% for the possibility that the patient with MS can develop syncope. CONCLUSIONS Pathophysiological mechanisms underlying functional and structural disorders of autonomic nervous system in MS differ significantly. While preserved brainstem function is needed for development of syncope, structural disorders like OH could be associated with brainstem dysfunction.
Collapse
Affiliation(s)
- Mario Habek
- School of Medicine, University of Zagreb, Zagreb, Croatia; University Hospital Center Zagreb, Department of Neurology, Referral Center for Demyelinating Diseases of the Central Nervous System, Zagreb, Croatia.
| | - Magdalena Krbot Skorić
- University Hospital Center Zagreb, Department of Neurology, Referral Center for Demyelinating Diseases of the Central Nervous System, Zagreb, Croatia
| | - Luka Crnošija
- School of Medicine, University of Zagreb, Zagreb, Croatia
| | - Ivan Adamec
- University Hospital Center Zagreb, Department of Neurology, Referral Center for Demyelinating Diseases of the Central Nervous System, Zagreb, Croatia
| |
Collapse
|
10
|
Blanc JJ, Alboni P, Benditt DG. Vasovagal syncope in humans and protective reactions in animals. Europace 2015; 17:345-9. [DOI: 10.1093/europace/euu367] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
|
11
|
Del Pozzi AT, Schwartz CE, Tewari D, Medow MS, Stewart JM. Reduced cerebral blood flow with orthostasis precedes hypocapnic hyperpnea, sympathetic activation, and postural tachycardia syndrome. Hypertension 2014; 63:1302-8. [PMID: 24711524 DOI: 10.1161/hypertensionaha.113.02824] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Hyperventilation and reduced cerebral blood flow velocity can occur in postural tachycardia syndrome (POTS). We studied orthostatically intolerant patients, with suspected POTS, with a chief complaint of upright dyspnea. On the basis of our observations of an immediate reduction of cerebral blood flow velocity with orthostasis, we hypothesize that the resulting ischemic hypoxia of the carotid body causes chemoreflex activation, hypocapnic hyperpnea, sympathetic activation, and increased heart rate and blood pressure in this subset of POTS. We compared 11 dyspneic POTS subjects with 10 healthy controls during a 70° head-up tilt. In POTS subjects during initial orthostasis before blood pressure recovery; central blood volume and mean arterial pressure were reduced (P<0.025), resulting in a significant (P<0.001) decrease in cerebral blood flow velocity, which temporally preceded (17±6 s; P<0.025) a progressive increase in minute ventilation and decrease in end tidal CO2 (P<0.05) when compared with controls. Sympathoexcitation, measured by muscle sympathetic nerve activity, was increased in POTS (P<0.01) and inversely proportional to end tidal CO2 and resulted in an increase in heart rate (P<0.001), total peripheral resistance (P<0.025), and a decrease in cardiac output (P<0.025). The decrease in cerebral blood flow velocity and mean arterial pressure during initial orthostasis was greater (P<0.025) in POTS. Our data suggest that exaggerated initial central hypovolemia during initial orthostatic hypotension in POTS results in reduced cerebral blood flow velocity and postural hypocapnic hyperpnea that perpetuates cerebral ischemia. We hypothesize that sustained hypocapnia and cerebral ischemia produce sympathoexcitation, tachycardia, and a statistically significant increase in blood pressure.
Collapse
Affiliation(s)
- Andrew T Del Pozzi
- Center for Hypotension, 19 Bradhurst Ave, Suite 1600 S, Hawthorne, NY 10532.
| | | | | | | | | |
Collapse
|
12
|
Lucas SJE, Lewis NCS, Sikken ELG, Thomas KN, Ainslie PN. Slow breathing as a means to improve orthostatic tolerance: a randomized sham-controlled trial. J Appl Physiol (1985) 2013; 115:202-11. [DOI: 10.1152/japplphysiol.00128.2013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endogenous oscillations in blood pressure (BP) and cerebral blood flow have been associated with improved orthostatic tolerance. Although slow breathing induces such responses, it has not been tested as a therapeutic strategy to improve orthostatic tolerance. With the use of a randomized, crossover sham-controlled design, we tested the hypothesis that breathing at six breaths/min (vs. spontaneous breathing) would improve orthostatic tolerance via inducing oscillations in mean arterial BP (MAP) and cerebral blood flow. Sixteen healthy participants (aged 25 ± 4 yr; mean ± SD) had continuous beat-to-beat measurements of middle cerebral artery blood velocity (MCAv), BP (finometer), heart rate (ECG), and end-tidal carbon dioxide partial pressure during an incremental orthostatic stress test to presyncope by combining head-up tilt with incremental lower-body negative pressure. Tolerance time to presyncope was improved (+15%) with slow breathing compared with spontaneous breathing (29.2 ± 5.4 vs. 33.7 ± 6.0 min; P < 0.01). The improved tolerance was reflected in elevations in low-frequency (LF; 0.07-0.2 Hz) oscillations of MAP and mean MCAv, improved metrics of dynamic cerebrovascular control (increased LF phase and reduced LF gain), and a reduced rate of decline for MCAv (−0.60 ± 0.27 vs. −0.99 ± 0.51 cm·s−1·min−1; P < 0.01) and MAP (−0.50 ± 0.37 vs. −1.03 ± 0.80 mmHg/min; P = 0.01 vs. spontaneous breathing) across time from baseline to presyncope. Our findings show that orthostatic tolerance can be improved within healthy individuals with a simple, nonpharmacological breathing strategy. The mechanisms underlying this improvement are likely mediated via the generation of negative intrathoracic pressure during slow and deep breathing and the related beneficial impact on cerebrovascular and autonomic function.
Collapse
Affiliation(s)
- Samuel J. E. Lucas
- Department of Physiology, University of Otago, Dunedin, New Zealand
- School of Physical Education, University of Otago, Dunedin, New Zealand
- School of Sport and Exercise Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Nia C. S. Lewis
- Centre of Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Vancouver, British Columbia, Canada
- Research Institute of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom; and
| | - Elisabeth L. G. Sikken
- Department of Physiology, University of Otago, Dunedin, New Zealand
- Department of Physiology, Radboud University, Nijmegen Medical Centre, Nijmegen, the Netherlands
| | - Kate N. Thomas
- Department of Physiology, University of Otago, Dunedin, New Zealand
- School of Physical Education, University of Otago, Dunedin, New Zealand
| | - Philip N. Ainslie
- Centre of Heart, Lung and Vascular Health, School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia, Okanagan Campus, Vancouver, British Columbia, Canada
| |
Collapse
|
13
|
Ritz T, Meuret AE, Simon E. Cardiovascular activity in blood-injection-injury phobia during exposure: evidence for diphasic response patterns? Behav Res Ther 2013; 51:460-8. [PMID: 23747585 DOI: 10.1016/j.brat.2013.03.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Revised: 02/20/2013] [Accepted: 03/28/2013] [Indexed: 11/19/2022]
Abstract
Exposure to feared stimuli in blood-injection-injury (BII)-phobia is thought to elicit a diphasic response pattern, with an initial fight-flight-like cardiovascular activation followed by a marked deactivation and possible fainting (vasovagal syncope). However, studies have remained equivocal on the importance of such patterns. We therefore sought to determine the prevalence and clinical relevance of diphasic responses using criteria that require a true diphasic response to exceed cardiovascular activation of an emotional episode of a negative valence and to exceed deactivation of an emotionally neutral episode. Sixty BII-phobia participants and 20 healthy controls were exposed to surgery, anger and neutral films while measuring heart rate, blood pressure, respiratory pattern, and end-tidal partial pressure of carbon dioxide (as indicator of hyperventilation). Diphasic response patterns were observed in up to 20% of BII-phobia participants and 26.6% of healthy controls for individual cardiovascular parameters. BII-phobia participants with diphasic patterns across multiple parameters showed more fear of injections and blood draws, reported the strongest physical symptoms during the surgery film, and showed the strongest tendency to hyperventilate. Thus, although only a minority of individuals with BII phobia shows diphasic responses, their occurrence indicates significant distress. Respiratory training may add to the treatment of BII phobia patients that show diphasic response patterns.
Collapse
Affiliation(s)
- Thomas Ritz
- Department of Psychology, Southern Methodist University, P.O. Box 750442, Dallas, TX 75275-0442, USA.
| | | | | |
Collapse
|
14
|
Stewart JM. Update on the theory and management of orthostatic intolerance and related syndromes in adolescents and children. Expert Rev Cardiovasc Ther 2013; 10:1387-99. [PMID: 23244360 DOI: 10.1586/erc.12.139] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Orthostasis means standing upright. One speaks of orthostatic intolerance (OI) when signs, such as hypotension, and symptoms, such as lightheadedness, occur when upright and are relieved by recumbence. The experience of transient mild OI is part of daily life. 'Initial orthostatic hypotension' on rapid standing is a normal form of OI. However, other people experience OI that seriously interferes with quality of life. These include episodic acute OI, in the form of postural vasovagal syncope, and chronic OI, in the form of postural tachycardia syndrome. Less common is neurogenic orthostatic hypotension, which is an aspect of autonomic failure. Normal orthostatic physiology and potential mechanisms for OI are discussed, including forms of sympathetic hypofunction, forms of sympathetic hyperfunction and OI that results from regional blood volume redistribution. General and specific treatment options are proposed.
Collapse
Affiliation(s)
- Julian M Stewart
- Departments of Pediatrics, Physiology and Medicine, The Maria Fareri Childrens Hospital and New York Medical College, Valhalla, NY, USA.
| |
Collapse
|
15
|
Abstract
The autonomic nervous system, adequate blood volume, and intact skeletal and respiratory muscle pumps are essential components for rapid cardiovascular adjustments to upright posture (orthostasis). Patients lacking sufficient blood volume or having defective sympathetic adrenergic vasoconstriction develop orthostatic hypotension (OH), prohibiting effective upright activities. OH is one form of orthostatic intolerance (OI) defined by signs, such as hypotension, and symptoms, such as lightheadedness, that occur when upright and are relieved by recumbence. Mild OI is commonly experienced during intercurrent illnesses and when standing up rapidly. The latter is denoted "initial OH" and represents a normal cardiovascular adjustment to the blood volume shifts during standing. Some people experience episodic acute OI, such as postural vasovagal syncope (fainting), or chronic OI, such as postural tachycardia syndrome, which can significantly reduce quality of life. The lifetime incidence of ≥1 fainting episodes is ∼40%. For the most part, these episodes are benign and self-limited, although frequent syncope episodes can be debilitating, and injury may occur from sudden falls. In this article, mechanisms for OI having components of adrenergic hypofunction, adrenergic hyperfunction, hyperpnea, and regional blood volume redistribution are discussed. Therapeutic strategies to cope with OI are proposed.
Collapse
Affiliation(s)
- Julian M. Stewart
- Departments of Pediatrics, Physiology, and Medicine, The Maria Fareri Children’s Hospital and New York Medical College, Valhalla, New York
| |
Collapse
|
16
|
Zuj KA, Arbeille P, Shoemaker JK, Hughson RL. Cerebral critical closing pressure and CO2 responses during the progression toward syncope. J Appl Physiol (1985) 2013; 114:801-7. [DOI: 10.1152/japplphysiol.01181.2012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Syncope from sustained orthostasis results from cerebral hypoperfusion associated with reductions in arterial pressure at the level of the brain (BPMCA) and reductions in arterial CO2 as reflected by end-tidal values (PetCO2). It was hypothesized that reductions in PetCO2 increase cerebrovascular tone before a drop in BPMCA that ultimately leads to syncope. Twelve men (21–42 yr of age) completed an orthostatic tolerance test consisting of head-up tilt and progressive lower body negative pressure to presyncope, before and after completing 5 days of continuous head-down bed rest (HDBR). Cerebral blood velocity (CBFV), BPMCA, and PetCO2 were continuously recorded throughout the test. Cerebrovascular indicators, cerebrovascular resistance, critical closing pressure (CrCP), and resistance area product (RAP), were calculated. Comparing from supine baseline to 6–10 min after the start of tilt, there were reductions in CBFV, PetCO2, BPMCA, and CrCP, an increase in RAP, and no change in cerebrovascular resistance index. Over the final 15 min before syncope in the pre-HDBR tests, CBFV and CrCP were significantly related to changes in PetCO2 ( r = 0.69 ± 0.17 and r = 0.63 ± 0.20, respectively), and BPMCA, which was not reduced until the last minute of the test, was correlated with a reduction in RAP ( r = 0.91 ± 0.09). Post-HDBR, tilt tolerance was markedly reduced, and changes in CBFV were dominated by a greater reduction in BPMCA with no relationships to PetCO2. Therefore, pre-HDBR, changes in PetCO2 with orthostasis contributed to increases in cerebrovascular tone and reductions in CBFV during the progression toward syncope, whereas, after 5 days of HDBR, orthostatic responses were dominated by changes in BPMCA.
Collapse
Affiliation(s)
- K. A. Zuj
- University of Waterloo, Waterloo, Ontario, Canada
| | | | | | | |
Collapse
|
17
|
|
18
|
Schwartz CE, Stewart JM. The arterial baroreflex resets with orthostasis. Front Physiol 2012; 3:461. [PMID: 23233840 PMCID: PMC3516802 DOI: 10.3389/fphys.2012.00461] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Accepted: 11/20/2012] [Indexed: 11/13/2022] Open
Abstract
The arterial baroreflexes, located in the carotid sinus and along the arch of the aorta, are essential for the rapid short term autonomic regulation of blood pressure. In the past, they were believed to be inactivated during exercise because blood pressure, heart rate, and sympathetic activity were radically changed from their resting functional relationships with blood pressure. However, it was discovered that all relationships between carotid sinus pressure and either HR or sympathetic vasoconstriction maintained their curvilinear sigmoidal shape but were reset or shifted so as to best defend BP during exercise. To determine whether resetting also occurs during orthostasis, we examined the arterial baroreflexes measured supine and upright tilt. We studied the relationships between systolic BP and HR (the cardiovagal baroreflex), mean BP, and ventilation (the ventilatory baroreflex) and diastolic BP and sympathetic nerve activity (the sympathetic baroreflex). We accomplished these measurements by using the modified Oxford method in which BP was rapidly varied with bolus injections of sodium nitroprusside followed 1 min later by bolus injections of phenylephrine. Both the cardiovagal and ventilatory baroreflexes were “reset” with no change in gain or response range. In contrast, the sympathetic baroreflex was augmented as well as shifted causing an increase in peripheral resistance that improved the subjects’ defense against hypotension. This contrasts with findings during exercise in which peripheral resistance in active skeletal muscle is not increased. This difference is likely selective for exercising muscle and may represent the actions of functional sympatholysis by which exercise metabolites interfere with adrenergic vasoconstriction.
Collapse
Affiliation(s)
- Christopher E Schwartz
- Department of Physiology, The Center for Hypotension, New York Medical College Valhalla, NY, USA ; Department of Pediatrics, The Center for Hypotension, New York Medical College Valhalla, NY, USA
| | | |
Collapse
|
19
|
Abstract
Sympathetic circulatory control is key to the rapid cardiovascular adjustments that occur within seconds of standing upright (orthostasis) and which are required for bipedal stance. Indeed, patients with ineffective sympathetic adrenergic vasoconstriction rapidly develop orthostatic hypotension, prohibiting effective upright activities. One speaks of orthostatic intolerance (OI) when signs, such as hypotension, and symptoms, such as lightheadedness, occur when upright and are relieved by recumbence. The experience of transient mild OI is part of daily life. However, many people experience episodic acute OI as postural faint or chronic OI in the form of orthostatic tachycardia and orthostatic hypotension that significantly reduce the quality of life. Potential mechanisms for OI are discussed including forms of sympathetic hypofunction, forms of sympathetic hyperfunction, and OI that results from regional blood volume redistribution attributable to regional adrenergic hypofunction.
Collapse
Affiliation(s)
- Julian M Stewart
- Departments of Physiology, Pediatrics and Medicine, New York Medical College, Valhalla, NY, USA. mail:
| |
Collapse
|
20
|
Increased pulsatile cerebral blood flow, cerebral vasodilation, and postsyncopal headache in adolescents. J Pediatr 2011; 159:656-62.e1. [PMID: 21596391 PMCID: PMC3160518 DOI: 10.1016/j.jpeds.2011.04.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/15/2010] [Revised: 03/28/2011] [Accepted: 04/06/2011] [Indexed: 12/15/2022]
Abstract
OBJECTIVE We hypothesize that, after a sudden decrease in cerebral blood flow velocity (CBFV) in adolescents, a faint, rapid hyperemic pulsatile CBFV occurs upon the patient's return to the supine position and is associated with postsyncopal headache. STUDY DESIGN This case-control study involved 16 adolescent subjects with a history of fainting and headaches. We induced fainting during 70° tilt-table testing and measured mean arterial pressure, heart rate, end-tidal CO(2), and CBFV. Fifteen control subjects were similarly evaluated with a tilt but did not faint, and comparisons with fainters were made at equivalent defined time points. RESULTS Baseline values were similar between the groups. Upon fainting, mean arterial pressure decreased 49% in the patients who fainted vs 6% in controls (P < .001). The heart rate decreased 15% in fainters and increased 35% in controls (P < .001). In patients who fainted, cerebrovascular critical closing pressure increased markedly, which resulted in reduced diastolic (-66%) and mean CBFV (-46%) at faint; systolic CBFV was similar to controls. Pulsatile CBFV (systolic-diastolic CBFV) increased 38% in fainters, which caused flow-mediated dilatation of cerebral vessels. When the fainters returned to the supine position, CBFV exhibited increased systolic and decreased diastolic flows compared with controls (P < .02). CONCLUSION Increased pulsatile CBFV during and after faint may cause postsyncopal cerebral vasodilation and headache.
Collapse
|
21
|
Lagi A, Cencetti S, Cartei A. What Happens before Syncope? Study of the Time Frame Preceding Vasovagal Syncope. ISRN CARDIOLOGY 2011; 2011:659787. [PMID: 22347649 PMCID: PMC3262513 DOI: 10.5402/2011/659787] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Accepted: 03/18/2011] [Indexed: 11/30/2022]
Abstract
Objective. The events characterizing the very last part of the vasovagal crisis has not been determined. The aim of the study was to analyze the variations in respiratory pattern preceding the vaso-vagal syncope full-blown and the relationship between cardiovascular functions in order to assess the temporal sequence. Methods. Eleven consecutive patients were studied. Heart rate, arterial pressure, respiratory frequency, tidal volume, carbon dioxide, and oxygen saturation in time domain from supine and standing recordings were analyzed. Results. The respiratory activity is different in the time frame preceding syncope, both in VT and breathing rate, and that the increase of the lung ventilation does not influence the baroreflex control during the presyncopal period but may be cause of the baroreflex failure during the full-blown syncope.
Collapse
Affiliation(s)
- Alfonso Lagi
- Dipartimento di Medicina Interna, Ospedale Santa Maria Nuova, Piazza S. Maria Nuova, 50100 Firenze, Italy
| | - Simone Cencetti
- Dipartimento di Medicina Interna, Ospedale Santa Maria Nuova, Piazza S. Maria Nuova, 50100 Firenze, Italy
| | - Alessandro Cartei
- Dipartimento di Medicina Interna, Ospedale Santa Maria Nuova, Piazza S. Maria Nuova, 50100 Firenze, Italy
| |
Collapse
|
22
|
Stewart JM, Rivera E, Clarke DA, Baugham IL, Ocon AJ, Taneja I, Terilli C, Medow MS. Ventilatory baroreflex sensitivity in humans is not modulated by chemoreflex activation. Am J Physiol Heart Circ Physiol 2011; 300:H1492-500. [PMID: 21317304 DOI: 10.1152/ajpheart.01217.2010] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Increasing arterial blood pressure (AP) decreases ventilation, whereas decreasing AP increases ventilation in experimental animals. To determine whether a "ventilatory baroreflex" exists in humans, we studied 12 healthy subjects aged 18-26 yr. Subjects underwent baroreflex unloading and reloading using intravenous bolus sodium nitroprusside (SNP) followed by phenylephrine ("Oxford maneuver") during the following "gas conditions:" room air, hypoxia (10% oxygen)-eucapnia, and 30% oxygen-hypercapnia to 55-60 Torr. Mean AP (MAP), heart rate (HR), cardiac output (CO), total peripheral resistance (TPR), expiratory minute ventilation (V(E)), respiratory rate (RR), and tidal volume were measured. After achieving a stable baseline for gas conditions, we performed the Oxford maneuver. V(E) increased from 8.8 ± 1.3 l/min in room air to 14.6 ± 0.8 l/min during hypoxia and to 20.1 ± 2.4 l/min during hypercapnia, primarily by increasing tidal volume. V(E) doubled during SNP. CO increased from 4.9 ± .3 l/min in room air to 6.1 ± .6 l/min during hypoxia and 6.4 ± .4 l/min during hypercapnia with decreased TPR. HR increased for hypoxia and hypercapnia. Sigmoidal ventilatory baroreflex curves of V(E) versus MAP were prepared for each subject and each gas condition. Averaged curves for a given gas condition were obtained by averaging fits over all subjects. There were no significant differences in the average fitted slopes for different gas conditions, although the operating point varied with gas conditions. We conclude that rapid baroreflex unloading during the Oxford maneuver is a potent ventilatory stimulus in healthy volunteers. Tidal volume is primarily increased. Ventilatory baroreflex sensitivity is unaffected by chemoreflex activation, although the operating point is shifted with hypoxia and hypercapnia.
Collapse
Affiliation(s)
- Julian M Stewart
- Department of Pediatrics, New York Medical College, Valhalla, USA.
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Zhang P, Huang G, Shi X. Cerebral vasoreactivity during hypercapnia is reset by augmented sympathetic influence. J Appl Physiol (1985) 2010; 110:352-8. [PMID: 21071587 DOI: 10.1152/japplphysiol.00802.2010] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sympathetic nerve activity influences cerebral blood flow, but it is unknown whether augmented sympathetic nerve activity resets cerebral vasoreactivity to hypercapnia. This study tested the hypothesis that cerebral vasodilation during hypercapnia is restrained by lower-body negative pressure (LBNP)-stimulated sympathoexcitation. Cerebral hemodynamic responses were assessed in nine healthy volunteers [age 25 yr (SD 3)] during rebreathing-induced increases in partial pressure of end-tidal CO(2) (Pet(CO(2))) at rest and during LBNP. Cerebral hemodynamic responses were determined by changes in flow velocity of middle cerebral artery (MCAV) using transcranial Doppler sonography and in regional cerebral tissue oxygenation (ScO(2)) using near-infrared spectroscopy. Pet(CO(2)) values during rebreathing were similarly increased from 41.9 to 56.5 mmHg at rest and from 40.7 to 56.0 mmHg during LBNP of -15 Torr. However, the rates of increases in MCAV and in ScO(2) per unit increase in Pet(CO(2)) (i.e., the slopes of MCAV/Pet(CO(2)) and ScO(2)/Pet(CO(2))) were significantly (P ≤0.05) decreased from 2.62 ± 0.16 cm·s(-1)·mmHg(-1) and 0.89 ± 0.10%/mmHg at rest to 1.68 ± 0.18 cm·s(-1)·mmHg(-1) and 0.63 ± 0.07%/mmHg during LBNP. In conclusion, the sensitivity of cerebral vasoreactivity to hypercapnia, in terms of the rate of increases in MCAV and in ScO(2), is diminished by LBNP-stimulated sympathoexcitation.
Collapse
Affiliation(s)
- Peizhen Zhang
- Department of Integrative Physiology, UNT Health Science Center, Fort Worth, TX 76107, USA
| | | | | |
Collapse
|
24
|
Near infrared spectroscopy: guided tilt table testing for syncope. Pediatr Cardiol 2010; 31:674-9. [PMID: 20204346 DOI: 10.1007/s00246-010-9683-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Accepted: 02/10/2010] [Indexed: 10/19/2022]
Abstract
Syncope is transient loss of consciousness. Neurocardiogenic syncope (NCS) is the most common cause of syncope. Head-up tilt-table test (HUTT) has been used to demonstrate physiologic events during graded orthostatic challenge in individuals with significant handicap from NCS. Near-infrared spectroscopy (NIRS) provides a noninvasive, continuous method to monitor trends of regional tissue oxygenation (rSO2). We hypothesize that multisite NIRS monitoring will show differential desaturation patterns in the brain and renal vascular beds during postural stresses. All patients age 7-21 years old scheduled to undergo HUTT were recruited. Two probes for NIRS monitoring were placed on the forehead and above the left paravertebral level at the T10 to L1 space. These leads were attached to the Somanetics monitor (Somanetics, Troy MI). Tissue saturations (rSO2) obtained at two sites were recorded at rest, during the test, and throughout a 5-min recovery period. All data routinely obtained in HUTT were included in the research study database. Thirteen patients were recruited. The average age was 12.9 years. Five patients had a positive tilt-table test. The patients with syncope had rSO2 trends distinctly different from the normal subjects. In these patients, cerebral rSO2 showed a sudden decreasing trend from hypoperfusion, soon followed by various clinical symptoms. The cerebral rSO2 trend, which showed a dramatic increase, was paralleled by renal rSO2. These rSO2 trends were progressive until the patient was brought back to the supine position, which resulted in the rSO2 in both beds returning to baseline. Multisite NIRS-guided HUTT shows differential trends in the different vascular beds during postural gravitational stresses, and these patterns underlie the systemic oxygen consumption to flow-coupling dynamics observed during syncope.
Collapse
|
25
|
Lewis NCS, Atkinson G, Lucas SJE, Grant EJM, Jones H, Tzeng YC, Horsman H, Ainslie PN. Diurnal variation in time to presyncope and associated circulatory changes during a controlled orthostatic challenge. Am J Physiol Regul Integr Comp Physiol 2010; 299:R55-61. [DOI: 10.1152/ajpregu.00030.2010] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Epidemiological data indicate that the risk of neurally mediated syncope is substantially higher in the morning. Syncope is precipitated by cerebral hypoperfusion, yet no chronobiological experiment has been undertaken to examine whether the major circulatory factors, which influence perfusion, show diurnal variation during a controlled orthostatic challenge. Therefore, we examined the diurnal variation in orthostatic tolerance and circulatory function measured at baseline and at presyncope. In a repeated-measures experiment, conducted at 0600 and 1600, 17 normotensive volunteers, aged 26 ± 4 yr (mean ± SD), rested supine at baseline and then underwent a 60° head-up tilt with 5-min incremental stages of lower body negative pressure until standardized symptoms of presyncope were apparent. Pretest hydration status was similar at both times of day. Continuous beat-to-beat measurements of cerebral blood flow velocity, blood pressure, heart rate, stroke volume, cardiac output, and end-tidal Pco2 were obtained. At baseline, mean cerebral blood flow velocity was 9 ± 2 cm/s (15%) lower in the morning than the afternoon ( P < 0.0001). The mean time to presyncope was shorter in the morning than in the afternoon (27.2 ± 10.5 min vs. 33.1 ± 7.9 min; 95% CI: 0.4 to 11.4 min, P = 0.01). All measurements made at presyncope did not show diurnal variation ( P > 0.05), but the changes over time (from baseline to presyncope time) in arterial blood pressure, estimated peripheral vascular resistance, and α-index baroreflex sensitivity were greater during the morning tests ( P < 0.05). These data indicate that tolerance to an incremental orthostatic challenge is markedly reduced in the morning due to diurnal variations in the time-based decline in blood pressure and the initial cerebral blood flow velocity “reserve” rather than the circulatory status at eventual presyncope. Such information may be used to help identify individuals who are particularly prone to orthostatic intolerance in the morning.
Collapse
Affiliation(s)
- N. C. S. Lewis
- Research Institute of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
| | - G. Atkinson
- Research Institute of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
| | - S. J. E. Lucas
- Department of Physiology and
- School of Physical Education, University of Otago, Dunedin, New Zealand
| | | | - H. Jones
- Research Institute of Sport and Exercise Science, Liverpool John Moores University, Liverpool, United Kingdom
| | - Y. C. Tzeng
- Physiological Rhythms Unit, Department of Surgery and Anaesthesia, University of Otago, Wellington, New Zealand; and
| | - H. Horsman
- Physiological Rhythms Unit, Department of Surgery and Anaesthesia, University of Otago, Wellington, New Zealand; and
| | - P. N. Ainslie
- Department of Human Kinetics, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, Canada
| |
Collapse
|
26
|
Ritz T, Meuret AE, Ayala ES. The psychophysiology of blood-injection-injury phobia: looking beyond the diphasic response paradigm. Int J Psychophysiol 2010; 78:50-67. [PMID: 20576505 DOI: 10.1016/j.ijpsycho.2010.05.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2010] [Revised: 04/29/2010] [Accepted: 05/20/2010] [Indexed: 10/19/2022]
Abstract
Blood-injection-injury (BII) phobia is an anxiety disorder that may be accompanied by vasovagal fainting during confrontation with the feared stimuli. The underlying pattern of autonomic regulation has been characterized as a diphasic response, with initial increases in heart rate and blood pressure that are typical of a fight-flight response, and subsequent drops in blood pressure and/or heart rate that may precipitate vasovagal fainting. Tensing skeletal muscles of the arms, legs, and trunk (applied tension) has been proposed as a technique to cope with this dysregulation. This review critically examines the empirical basis for the diphasic response and its treatment by applied tension in BII phobia. An alternative perspective on the psychophysiology of BII phobia and vasovagal fainting is offered by focusing on hypocapnia that leads to cerebral blood flow reductions, a perspective supported by research on neurocardiogenic and orthostatically-induced syncope. The evidence may indicate a role for respiration-focused coping techniques in BII phobia.
Collapse
Affiliation(s)
- Thomas Ritz
- Department of Psychology, Southern Methodist University, P.O. Box 750442, Dallas, TX 75275-0442, USA.
| | | | | |
Collapse
|
27
|
Ainslie PN, Willie CK, Tzeng YC. Role of SNA in the pathophysiology of cardiovascular collapse during syncope: muscle vs. brain. J Physiol 2009; 587:5795-6. [PMID: 19959554 DOI: 10.1113/jphysiol.2009.182667] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
|
28
|
Abstract
The response of the cerebral vasculature to exercise is different from the other peripheral vasculature (e.g., muscle); the cerebral vasculature has a small vascular bed and is strongly regulated by cerebral autoregulation and the partial pressure of arterial carbon dioxide. This review focuses on the integrative mechanisms underlying the regulation of cerebral blood flow during exercise.
Collapse
|
29
|
Ogoh S, Ainslie PN. Cerebral blood flow during exercise: mechanisms of regulation. J Appl Physiol (1985) 2009; 107:1370-80. [PMID: 19729591 DOI: 10.1152/japplphysiol.00573.2009] [Citation(s) in RCA: 343] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The response of cerebral vasculature to exercise is different from other peripheral vasculature; it has a small vascular bed and is strongly regulated by cerebral autoregulation and the partial pressure of arterial carbon dioxide (Pa(CO(2))). In contrast to other organs, the traditional thinking is that total cerebral blood flow (CBF) remains relatively constant and is largely unaffected by a variety of conditions, including those imposed during exercise. Recent research, however, indicates that cerebral neuronal activity and metabolism drive an increase in CBF during exercise. Increases in exercise intensity up to approximately 60% of maximal oxygen uptake produce elevations in CBF, after which CBF decreases toward baseline values because of lower Pa(CO(2)) via hyperventilation-induced cerebral vasoconstriction. This finding indicates that, during heavy exercise, CBF decreases despite the cerebral metabolic demand. In contrast, this reduced CBF during heavy exercise lowers cerebral oxygenation and therefore may act as an independent influence on central fatigue. In this review, we highlight methodological considerations relevant for the assessment of CBF and then summarize the integrative mechanisms underlying the regulation of CBF at rest and during exercise. In addition, we examine how CBF regulation during exercise is altered by exercise training, hypoxia, and aging and suggest avenues for future research.
Collapse
Affiliation(s)
- Shigehiko Ogoh
- Dept. of Biomedical Engineering, Toyo Univ., 2100 Kujirai, Kawagoe-shi, Saitama 350-8585, Japan.
| | | |
Collapse
|
30
|
Thomas KN, Cotter JD, Galvin SD, Williams MJA, Willie CK, Ainslie PN. Initial orthostatic hypotension is unrelated to orthostatic tolerance in healthy young subjects. J Appl Physiol (1985) 2009; 107:506-17. [DOI: 10.1152/japplphysiol.91650.2008] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The physiological challenge of standing upright is evidenced by temporary symptoms of light-headedness, dizziness, and nausea. It is not known, however, if initial orthostatic hypotension (IOH) and related symptoms associated with standing are related to the occurrence of syncope. Since IOH reflects immediate and temporary adjustments compared with the sustained adjustments during orthostatic stress, we anticipated that the severity of IOH would be unrelated to syncope. Following a standardized period of supine rest, healthy volunteers [ n = 46; 25 ± 5 yr old (mean ± SD)] were instructed to stand upright for 3 min, followed by 60° head-up tilt with lower-body negative pressure in 5-min increments of −10 mmHg, until presyncope. Beat-to-beat blood pressure (radial arterial or Finometer), middle cerebral artery blood velocity (MCAv), end-tidal Pco2, and cerebral oxygenation (near-infrared spectroscopy) were recorded continuously. At presyncope, although the reductions in mean arterial pressure, MCAv, and cerebral oxygenation were similar to those during IOH (40 ± 11 vs. 43 ± 12%; 36 ± 18 vs. 35 ± 13%; and 6 ± 5 vs. 4 ± 2%, respectively), the reduction in end-tidal CO2 was greater (−7 ± 6 vs. −4 ± 3 mmHg) and was related to the decline in MCAv ( R2 = 0.4; P < 0.05). While MCAv pulsatility was elevated with IOH, it was reduced at presyncope ( P < 0.05). The cardiorespiratory and cerebrovascular changes during IOH were unrelated to those at presyncope, and interestingly, there was no relationship between the hemodynamic changes and the incidence of subjective symptoms in either scenario. During IOH, the transient nature of physiological changes can be well tolerated; however, potentially mediated by a reduced MCAv pulsatility and greater degree of hypocapnic-induced cerebral vasoconstriction, when comparable changes are sustained, the development of syncope is imminent.
Collapse
|
31
|
Panerai RB. Transcranial Doppler for evaluation of cerebral autoregulation. Clin Auton Res 2009; 19:197-211. [PMID: 19370374 DOI: 10.1007/s10286-009-0011-8] [Citation(s) in RCA: 148] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Accepted: 03/13/2009] [Indexed: 12/14/2022]
Abstract
Transcranial Doppler ultrasound (TCD) can measure cerebral blood flow velocity in the main intracranial vessels non-invasively and with high accuracy. Combined with the availability of non-invasive devices for continuous measurement of arterial blood pressure, the relatively low cost, ease-of-use, and excellent temporal resolution of TCD have stimulated the development of new techniques to assess cerebral autoregulation in the laboratory or bedside using a dynamic approach, instead of the more classical 'static' method. Clinical applications have shown consistent results in certain conditions such as severe head injury and carotid artery disease. Studies in syncopal patients revealed a more complex pattern due to aetiological non-homogeneity and methodological limitations mainly due to inadequate sample-size. Different analytical models to quantify autoregulatory performance have also contributed to the diversity of results in the literature. The review concludes with specific recommendations for areas where further validation and research are needed to improve the reliability and usefulness of TCD in clinical practice.
Collapse
Affiliation(s)
- Ronney B Panerai
- Medical Physics Group, Department of Cardiovascular Sciences, University of Leicester, Leicester, UK.
| |
Collapse
|
32
|
Nowak JA, Ocon A, Taneja I, Medow MS, Stewart JM. Multiresolution wavelet analysis of time-dependent physiological responses in syncopal youths. Am J Physiol Heart Circ Physiol 2008; 296:H171-9. [PMID: 18996985 DOI: 10.1152/ajpheart.00963.2008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Our prior studies indicated that postural fainting relates to thoracic hypovolemia. A supranormal increase in initial vascular resistance was sustained by increased peripheral resistance until late during head-up tilt (HUT), whereas splanchnic resistance, cardiac output, and blood pressure (BP) decreased throughout HUT. Our aim in the present study was to investigate the alterations of baroreflex activity that occur in synchrony with the beat-to-beat time-dependent changes in heart rate (HR), BP, and total peripheral resistance (TPR). We proposed that changes of low-frequency Mayer waves reflect sympathetic baroreflex. We used DWT multiresolution analyses to measure their time dependence. We studied 22 patients, 13 to 21 yr old, 14 who fainted within 10 min of upright tilt (fainters) and 8 healthy control subjects. Multiresolution analysis was obtained of continuous BP, HR, and respirations as a function of time during 70 degrees upright tilt at different scales corresponding to frequency bands. Wavelet power was concentrated in scales corresponding to 0.125 and 0.25 Hz. A major difference from control subjects was observed in fainters at the 0.125 Hz AP scale, which progressively decreased from early HUT. The alpha index at 0.125 Hz was increased in fainters. RR interval 0.25 Hz power decreased in fainters and controls but was markedly increased in fainters with syncope and thereafter corresponding to increased vagal tone compared with control subjects at those times only. The data imply a rapid reduction in time-dependent sympathetic baroreflex activity in fainters but not control subjects during HUT.
Collapse
Affiliation(s)
- Jennifer A Nowak
- Pediatrics, Physiology, and Medicine, The Center for Hypotension, New York Medical College, Hawthorne, New York 10532, USA
| | | | | | | | | |
Collapse
|
33
|
Abstract
It was suggested half a century ago that electrical impulses from the lateral hypothalamic area stimulate breathing. It is now emerging that these effects may be mediated, at least in part, by neurons containing orexin neuropeptides (also known as hypocretins). These cells promote wakefulness and consciousness, and their loss results in narcolepsy. Recent data also show that orexin neurons directly project to respiratory centres in the brainstem, which express orexin receptors, and where injection of orexin stimulates breathing. Because orexin neurons receive inputs that signal metabolic, sleep/wake and emotional states, it is tempting to speculate that they may regulate breathing according to these parameters. Knockout of the orexin gene in mice reduces CO2-induced increases in breathing by approximately 50% and increases the frequency of spontaneous sleep apneas. The relationship between orexins and breathing may be bidirectional: the rate of breathing controls acid and CO2 levels, and these signals alter the electrical activity of orexin neurons in vitro. Overall, these findings suggest that orexins are important for the regulation of breathing and may potentially play a role in the pathophysiology and medical treatment of respiratory disorders.
Collapse
|
34
|
Taneja I, Medow MS, Glover JL, Raghunath NK, Stewart JM. Increased vasoconstriction predisposes to hyperpnea and postural faint. Am J Physiol Heart Circ Physiol 2008; 295:H372-81. [PMID: 18502909 DOI: 10.1152/ajpheart.00101.2008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Our prior studies indicated that postural fainting relates to splanchnic hypervolemia and thoracic hypovolemia during orthostasis. We hypothesized that thoracic hypovolemia causes excessive sympathetic activation, increased respiratory tidal volume, and fainting involving the pulmonary stretch reflex. We studied 18 patients 13-21 yr old, 11 who fainted within 10 min of upright tilt (fainters) and 7 healthy control subjects. We measured continuous blood pressure and heart rate, respiration by inductance plethysmography, end-tidal carbon dioxide (ET(CO(2))) by capnography, and regional blood flows and blood volumes using impedance plethysmography, and we calculated arterial resistance with patients supine and during 70 degrees upright tilt. Splanchnic resistance decreased until faint in fainters (44 +/- 8 to 21 +/- 2 mmHg.l(-1).min(-1)) but increased in control subjects (47 +/- 5 to 53 +/- 4 mmHg.l(-1).min(-1)). Percent change in splanchnic blood volume increased (7.5 +/- 1.0 vs. 3.0 +/- 11.5%, P < 0.05) after the onset of tilt. Upright tilt initially significantly increased thoracic, pelvic, and leg resistance in fainters, which subsequently decreased until faint. In fainters but not control subjects, normalized tidal volume (1 +/- 0.1 to 2.6 +/- 0.2, P < 0.05) and normalized minute ventilation increased throughout tilt (1 +/- 0.2 to 2.1 +/- 0.5, P < 0.05), whereas respiratory rate decreased (19 +/- 1 to 15 +/- 1 breaths/min, P < 0.05). Maximum tidal volume occurred just before fainting. The increase in minute ventilation was inversely proportionate to the decrease in ET(CO(2)). Our data suggest that excessive splanchnic pooling and thoracic hypovolemia result in increased peripheral resistance and hyperpnea in simple postural faint. Hyperpnea and pulmonary stretch may contribute to the sympathoinhibition that occurs at the time of faint.
Collapse
Affiliation(s)
- Indu Taneja
- Department of Pediatrics, New York Medical College, Hawthorne, NY 10532, USA.
| | | | | | | | | |
Collapse
|
35
|
Norcliffe-Kaufmann LJ, Kaufmann H, Hainsworth R. Enhanced vascular responses to hypocapnia in neurally mediated syncope. Ann Neurol 2008; 63:288-94. [PMID: 17823939 DOI: 10.1002/ana.21205] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE The susceptibility to suffer neurally mediated syncope and loss of consciousness varies markedly. In addition to vasodilatation and bradycardia, hyperventilation precedes loss of consciousness. The resultant hypocapnia causes cerebral vasoconstriction and peripheral vasodilatation. We postulate that more pronounced cerebral and peripheral vascular responses to reductions in arterial CO(2) levels underlie greater susceptibility to neurally mediated syncope. METHODS We compared vascular responses to CO(2) among 31 patients with histories of recurrent neurally mediated syncope and low orthostatic tolerance and 14 age- and sex-matched control subjects with no history of syncope and normal orthostatic tolerance. Vascular responses to CO(2) were calculated after all subjects had fully recovered and their blood pressures and heart rates were stable. We measured blood flow velocity in the middle cerebral artery (transcranial Doppler) and in the left brachial artery (brachial Doppler), and end-tidal CO(2) during voluntary hyperventilation and hypoventilation (end-tidal CO(2) from 21-45mm Hg), and determined the slopes of the relations. RESULTS Hypocapnia produced a significantly greater reduction in cerebral blood flow velocity and in forearm vascular resistance in patients with neurally mediated syncope than in control subjects. Opposite changes occurred in response to hypercapnia. In all subjects, the changes in cerebral blood flow velocity and forearm vasodilatation were inversely related with orthostatic tolerance. INTERPRETATION Susceptibility to neurally mediated syncope can be explained, at least in part, by enhanced cerebral vasoconstriction and peripheral vasodilatation in response to hypocapnia. This may have therapeutic implications.
Collapse
|
36
|
Abstract
Orthostatic hypotension (OH) occurs in 0.5% of individuals and as many as 7-17% of patients in acute care settings. Moreover, OH may be more prevalent in the elderly due to the increased use of vasoactive medications and the concomitant decrease in physiologic function, such as baroreceptor sensitivity. OH may result in the genesis of a presyncopal state or result in syncope. OH is defined as a reduction of systolic blood pressure (SBP) of at least 20 mm Hg or diastolic blood pressure (DBP) of at least 10 mm Hg within 3 minutes of standing. A review of symptoms, and measurement of supine and standing BP with appropriate clinical tests should narrow the differential diagnosis and the cause of OH. The fall in BP seen in OH results from the inability of the autonomic nervous system (ANS) to achieve adequate venous return and appropriate vasoconstriction sufficient to maintain BP. An evaluation of patients with OH should consider hypovolemia, removal of offending medications, primary autonomic disorders, secondary autonomic disorders, and vasovagal syncope, the most common cause of syncope. Although further research is necessary to rectify the disease process responsible for OH, patients suffering from this disorder can effectively be treated with a combination of nonpharmacologic treatment, pharmacologic treatment, and patient education. Agents such as fludrocortisone, midodrine, and selective serotonin reuptake inhibitors have shown promising results. Treatment for recurrent vasovagal syncope includes increased salt and water intake and various drug treatments, most of which are still under investigation.
Collapse
|
37
|
Verheyden B, Ector H, Aubert AE, Reybrouck T. Tilt training increases the vasoconstrictor reserve in patients with neurally mediated syncope evoked by head-up tilt testing. Eur Heart J 2008; 29:1523-30. [DOI: 10.1093/eurheartj/ehn134] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
38
|
Benedek K, Pálinkás A, Abrahám G, Beniczky S, Vécsei L, Rudas L. Pseudosyncope and pseudoseizure. Orv Hetil 2007; 148:1231-6. [PMID: 17588857 DOI: 10.1556/oh.2007.28001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A syncope gyakori kórkép, mely jelentős terheket ró az egészségügyre. Bár diagnosztikus eszközeink fejlődnek, az esetek egy kis hányadában az eszméletvesztés pontos oka az alapos kivizsgálás ellenére is rejtve marad. Az ismeretlen eredetű syncopék csoportjába tartozik a pszichogén álsyncope, mely – szemben a valódi syncopéval – nem jár az agyi keringés átmeneti zavarával. Az álsyncope valójában a konverziós betegség egyik megnyilvánulása, és mint ilyen, számos jellegzetességében osztozik az álgörcsrohammal. Az utóbbira ugyancsak jellemző, hogy a rohamok alatt hiányoznak a görcstevékenység jellegzetes neurológiai és EEG-manifesztációi. A két megjelenési forma esetenként ugyanazon betegben váltakozva léphet fel. Közleményünkben egy álsyncopékat és álgörcsrohamokat egyaránt produkáló beteg történetét mutatjuk be. Az eset kapcsán áttekintjük az álsyncope irodalmát, és felhívjuk a figyelmet az interdiszciplináris diagnosztikus megközelítés szerepére.
Collapse
Affiliation(s)
- Krisztina Benedek
- Szegedi Tudományegyetem, Szent-Györgyi Albert Orvos- és Gyógyszerésztudományi Centrum, Altalános Orvostudományi Kar Neurológiai Klinika, Szeged
| | | | | | | | | | | |
Collapse
|
39
|
Abstract
Whatever the pathogenesis of syncope is, the ultimate common cause leading to loss of consciousness is insufficient cerebral perfusion with a critical reduction of blood flow to the reticular activating system. Brain circulation has an autoregulation system that keeps cerebral blood flow constant over a wide range of systemic blood pressures. Normally, if blood pressure decreases, autoregulation reacts with a reduction in cerebral vascular resistance, in an attempt to prevent cerebral hypoperfusion. However, in some cases, particularly in neurally mediated syncope, it can also be harmful, being actively implicated in a paradox reflex that induces an increase in cerebrovascular resistance and contributes to the critical reduction of cerebral blood flow. This review outlines the anatomic structures involved in cerebral autoregulation, its mechanisms, in normal and pathologic conditions, and the noninvasive neuroimaging techniques used in the study of cerebral circulation and autoregulation. An emphasis is placed on the description of autoregulation pathophysiology in orthostatic and neurally mediated syncope.
Collapse
|
40
|
Diehl RR. Wave reflection analysis of the human cerebral circulation during syncope. Auton Neurosci 2007; 132:63-9. [PMID: 16978926 DOI: 10.1016/j.autneu.2006.08.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2006] [Revised: 08/02/2006] [Accepted: 08/07/2006] [Indexed: 10/24/2022]
Abstract
Up till now, the presence of wave reflection of pressure and flow waves was not considered in studies on the cerebral circulation. This study tested the hypothesis whether the typical changes in cerebral blood flow velocity (CBFV) seen in patients during vasovagal syncope can be explained by the emergence of a wave reflection site in the cerebrovascular vessels. Continuous recordings of peripheral blood pressure (ABP, by Finapres) and CBFV (by transcranial Doppler) of 20 control subjects and 10 patients with syncope during tilt table testing were analyzed. Wave reflection analysis (WRA) consisted of a multivariate regression analysis with CBFV as dependent variable and simultaneous ABP as well as delayed ABP (by systematically varied time lags) as independent variables. The time delay yielding the best prediction of CBFV was interpreted as the reflection time. A univariate regression analysis with only simultaneous ABP as independent variable served as control method. In patients and controls CBFV during supine position could be explained sufficiently (explained variance=88-90%) by univariate regression without improvement by WRA. During syncope, multivariate regression improved the prediction of CBFV (explained variance=58% with univariate and 77% with multivariate regression) in 9 of 10 patients. The mean reflection time was 160 ms. The results can be explained by a collapse of the distal bridging veins during systemic hypotension giving rise to a pressure wave moving backward with a resulting distortion of the flow wave. In particular, the WRA model could account for the characteristic changes in the diastolic flow shape during syncope.
Collapse
Affiliation(s)
- Rolf R Diehl
- Autonomic Laboratory, Department of Neurology, Alfried Krupp Krankenhaus, Alfried-Krupp Strasse 21, 45117 Essen, Germany.
| |
Collapse
|
41
|
Parry SW, Steen N, Baptist M, Fiaschi KA, Parry O, Kenny RA. Cerebral autoregulation is impaired in cardioinhibitory carotid sinus syndrome. Heart 2006; 92:792-7. [PMID: 16449521 PMCID: PMC1860657 DOI: 10.1136/hrt.2004.053348] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
OBJECTIVES To compare changes in cerebral autoregulation in response to controlled, lower body negative pressure-induced hypotension in patients with carotid sinus syndrome (CSS) and case controls. DESIGN Prospective case controlled study. SETTING Secondary and tertiary referral falls and syncope service. PATIENTS 17 consecutive patients with CSS and 11 asymptomatic controls. INTERVENTIONS Hypotension insufficient to cause syncope induced by lower body negative pressure (minimum 30 mm Hg fall in systolic blood pressure (SBP)) during concomitant transcranial Doppler ultrasonography. MAIN OUTCOME MEASURES Cerebral autoregulation (systolic, diastolic and mean middle cerebral arterial blood flow velocities and cerebrovascular resistance) with continuous end-tidal carbon dioxide and haemodynamic monitoring. RESULTS Cerebral autoregulatory indices differed significantly between patients with CSS and controls. Systolic, diastolic and middle cerebral arterial blood flow velocities were, respectively, 9.2 m/s (95% confidence interval (CI) 2.9 to 15.4 m/s), 4.7 m/s (95% CI 1.5 to 7.9 m/s) and 6.9 m/s (95% CI 2.5 to 11.4 m/s) slower in patients with CSS. Cerebrovascular resistance was significantly greater in patients with CSS than in controls at SBP nadir and suction release; differences were 0.9 mm Hg/m/s (95% CI 0.0 to 1.7 mm Hg/m/s) and 0.8 mm Hg/m/s (95% CI 0.0 to 1.7 mm Hg/m/s), respectively. End-tidal carbon dioxide and systemic haemodynamic variables were similar for patients and controls at baseline and during lower body negative pressure. CONCLUSIONS Cerebral autoregulation is altered in patients with CSS. This difference may have aetiological implications in the differential presentation with falls and drop attacks rather than syncope.
Collapse
Affiliation(s)
- S W Parry
- Cardiovascular Investigation Unit, Royal Victoria Infirmary, Newcastle upon Tyne, UK.
| | | | | | | | | | | |
Collapse
|
42
|
Guo H, Tierney N, Schaller F, Raven PB, Smith SA, Shi X. Cerebral autoregulation is preserved during orthostatic stress superimposed with systemic hypotension. J Appl Physiol (1985) 2006; 100:1785-92. [PMID: 16424075 DOI: 10.1152/japplphysiol.00690.2005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We sought to determine whether cerebral autoregulation (CA) is compromised during orthostatic stress superimposed with systemic hypotension. Transient systemic hypotension was produced by deflation of thigh cuffs previously inflated to suprasystolic pressure, combined with or without lower body negative pressure (LBNP). Cardiac output (CO) decreased from a baseline of 5.0+/-0.5 l/min by -8.3+/-1.7, -19.2+/-2.0, and -30.6+/-3.4% during LBNP of -15, -30, and -50 Torr, respectively. Mean arterial pressure (MAP) was maintained during LBNP, despite decreases in systolic and pulse pressures. Middle cerebral arterial blood flow velocity (VMCA) decreased significantly from a baseline of 64+/-3 to 58+/-4 cm/s (-9.7+/-2.4%) at -50 Torr of LBNP. The reduction in VMCA was associated with a decrease in regional cerebral O2 saturation. However, the percent decrease in VMCA was markedly less than that of CO. This suggests that the magnitude of the change in VMCA (an index of cerebral blood flow) is less than would be predicted, given the decrease in CO. Transient systemic hypotension decreased MAP by -21+/-2, -24+/-2, -28+/-3, and -26+/-3% at rest and during LBNP of -15, -30, and -50 Torr, respectively. Likewise, this acute hypotension resulted in decreases in VMCA of -20+/-2, -21+/-2, -24+/-25, and -19+/-2% and regional cerebral O2 saturation of -5+/-1, -6+/-1, -6+/-1, and -7+/-2% at rest and during LBNP of -15, -30, and -50 Torr, respectively. Complete recovery of VMCA to baseline values following transient hypotension (ranging from 5 to 8 s) occurred significantly earlier compared with MAP (from 10 to 12 s). No subjects experienced syncope during acute hypotension. We conclude that CA is preserved during LBNP, superimposed with transient systemic hypotension, despite the decrease in VMCA associated with sustained central hypovolemia in normal healthy individuals. This preserved CA is vital for the prevention of orthostatic syncope.
Collapse
Affiliation(s)
- Hong Guo
- Department of Integrative Physiology, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
| | | | | | | | | | | |
Collapse
|
43
|
Abstract
Involvement of cerebral vasoconstriction confirms the complexity of the pathophysiology of neurally mediated syncope, and the need to adopt a comprehensive approach to the study of this problem.
Collapse
|
44
|
Mecarelli O, Pulitano P, Vicenzini E, Vanacore N, Accornero N, De Marinis M. Observations on EEG patterns in neurally-mediated syncope: an inspective and quantitative study. Neurophysiol Clin 2004; 34:203-7. [PMID: 15639129 DOI: 10.1016/j.neucli.2004.09.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2004] [Accepted: 09/06/2004] [Indexed: 11/18/2022] Open
Abstract
We performed an observational EEG study in 43 patients with neurally-mediated syncope in basal condition and during hyperventilation (HV), and compared it with 32 healthy controls. On blind analysis at rest, EEG was classified as normal in 47% of patients (vs. 94% of controls, P < 0.001). More abundant and pronounced delta-theta activities and alpha slowing were found in patients than in control subjects on both visual inspection and quantitative spectral analysis. During prolonged HV, the EEG remained normal in 21% of patients only. Slow activities became more evident in patients than in control subjects, and intermittent rhythmic delta activity appeared in 40% of syncopal patients. These "pseudoparoxysmal" EEG changes differed from the common slowings induced by HV in adult subjects and were not observed in our control subjects. Moreover, these distinctive EEG changes, a common finding in syncopal patients, could not be confused with epileptiform activity of any kind. Further studies will clarify the pathophysiology of these EEG modifications.
Collapse
Affiliation(s)
- O Mecarelli
- Department of Neurological Sciences, La Sapienza University, Viale Regina Elena, 336, 00161 Rome, Italy.
| | | | | | | | | | | |
Collapse
|
45
|
Wang X, Richardson L, Krishnamurthy S, Pennington K, Evans J, Bruce E, Abraham W, Bhakta D, Patwardhan A. Orthostatic modification of ventilatory dynamic response to carbon dioxide perturbations. Auton Neurosci 2004; 116:76-83. [PMID: 15556841 DOI: 10.1016/j.autneu.2004.09.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2004] [Revised: 07/08/2004] [Accepted: 09/28/2004] [Indexed: 10/26/2022]
Abstract
In order to determine whether changes in ventilatory control contribute to the observed decrease in arterial partial pressure of carbon dioxide (PaCO(2)) during head up tilt, we assessed ventilatory dynamic sensitivity to changes in PaCO(2) during supine and 70 degrees passive head up tilt. In 24 adult normals, we stimulated the ventilatory control system by switching inspired CO(2) between room air and room air+5% CO(2) in a pseudo random binary sequence. A Box-Jenkins model was used to compute ventilatory response to CO(2). Airflow, CO(2), non-invasive beat by beat blood pressure, ECG and cerebral blood flow velocity (Doppler) were recorded. During tilt, sensitivity of the ventilatory controller to CO(2) disturbance increased (from 0.45 to 0.72 L/min/mm Hg, p<0.005); minute ventilation increased (7.63 to 8.47 L/min, p<0.01), end tidal CO(2) (ETCO(2)), cerebral blood flow velocity (CBF) and baroreflex sensitivity decreased (46.9 to 42.9 mm Hg, p<0.001; 84.9 to 72.9 cm/s, p<0.001; and 17.6 to 5.5 ms/mm Hg, p<0.001). The primary observation from our study was that the sensitivity of ventilatory control system to perturbations in ETCO(2) increased during tilt. Taken together with decrease in mean levels of ETCO(2) and an increase in minute ventilation, these results suggest that during tilt, a change in the regulated level or 'set point' of PaCO(2) may occur.
Collapse
Affiliation(s)
- Xue Wang
- Center for Biomedical Engineering, University of Kentucky, Lexington, KY 40506, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
46
|
LeMarbre G, Stauber S, Khayat RN, Puleo DS, Skatrud JB, Morgan BJ. Baroreflex-induced sympathetic activation does not alter cerebrovascular CO2 responsiveness in humans. J Physiol 2003; 551:609-16. [PMID: 12844511 PMCID: PMC2343219 DOI: 10.1113/jphysiol.2003.046987] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We investigated the effect of baroreflex-induced sympathetic activation, produced by lower body negative pressure (LBNP) at -40 mmHg, on cerebrovascular responsiveness to hyper- and hypocapnia in healthy humans. Transcranial Doppler ultrasound was used to measure blood flow velocity (CFV) in the middle cerebral artery during variations in end-tidal carbon dioxide pressure (PET,CO2) of +10, +5, 0, -5, and -10 mmHg relative to eupnoea. The slopes of the linear relationships between PET,CO2 and CFV were computed separately for hyper- and hypocapnia during the LBNP and no-LBNP conditions. LBNP decreased pulse pressure, but did not change mean arterial pressure. LBNP evoked an increase in ventilation that resulted in a 9 +/- 2 mmHg decrease in PET,CO2, which was corrected by CO2 supplementation of the inspired air. LBNP did not affect cerebrovascular CO2 response slopes during steady-state hypercapnia (3.14 +/- 0.24 vs. 2.96 +/- 0.26 cm s-1 mmHg-1) or hypocapnia (1.31 +/- 0.18 vs. 1.32 +/- 0.19 cm s-1 mmHg-1), or the CFV responses to voluntary apnoea (+51 +/- 19 vs. +50 +/- 18 %). Thus, cerebrovascular CO2 responsiveness was not altered by baroreflex-induced sympathetic activation. Our data challenge the concept that sympathetic activation restrains cerebrovascular responses to alterations in CO2 pressure.
Collapse
Affiliation(s)
- Gabrielle LeMarbre
- Department of Medicine, University of Wisconsin-Madison and the Middleton Veterans Affairs Administration Hospital, 53705, USA
| | | | | | | | | | | |
Collapse
|
47
|
Van Lieshout JJ, Wieling W, Karemaker JM, Secher NH. Syncope, cerebral perfusion, and oxygenation. J Appl Physiol (1985) 2003; 94:833-48. [PMID: 12571122 DOI: 10.1152/japplphysiol.00260.2002] [Citation(s) in RCA: 259] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During standing, both the position of the cerebral circulation and the reductions in mean arterial pressure (MAP) and cardiac output challenge cerebral autoregulatory (CA) mechanisms. Syncope is most often associated with the upright position and can be provoked by any condition that jeopardizes cerebral blood flow (CBF) and regional cerebral tissue oxygenation (cO(2)Hb). Reflex (vasovagal) responses, cardiac arrhythmias, and autonomic failure are common causes. An important defense against a critical reduction in the central blood volume is that of muscle activity ("the muscle pump"), and if it is not applied even normal humans faint. Continuous tracking of CBF by transcranial Doppler-determined cerebral blood velocity (V(mean)) and near-infrared spectroscopy-determined cO(2)Hb contribute to understanding the cerebrovascular adjustments to postural stress; e.g., MAP does not necessarily reflect the cerebrovascular phenomena associated with (pre)syncope. CA may be interpreted as a frequency-dependent phenomenon with attenuated transfer of oscillations in MAP to V(mean) at low frequencies. The clinical implication is that CA does not respond to rapid changes in MAP; e.g., there is a transient fall in V(mean) on standing up and therefore a feeling of lightheadedness that even healthy humans sometimes experience. In subjects with recurrent vasovagal syncope, dynamic CA seems not different from that of healthy controls even during the last minutes before the syncope. Redistribution of cardiac output may affect cerebral perfusion by increased cerebral vascular resistance, supporting the view that cerebral perfusion depends on arterial inflow pressure provided that there is a sufficient cardiac output.
Collapse
Affiliation(s)
- Johannes J Van Lieshout
- Cardiovascular Research Institute Amsterdam and Departments of Medicine and Physiology, Academic Medical Center, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
| | | | | | | |
Collapse
|
48
|
Frishman WH, Azer V, Sica D. Drug treatment of orthostatic hypotension and vasovagal syncope. HEART DISEASE (HAGERSTOWN, MD.) 2003; 5:49-64. [PMID: 12549988 DOI: 10.1097/01.hdx.0000050416.53995.43] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Orthostatic hypotension is a common problem, estimated to occur in 5 out of every 1000 individuals and in as many as 7% to 17% of patients in an acute care setting. Moreover, orthostatic hypotension may be more prominent in elderly patients due to the increased intake of vasoactive medications and concomitant decrease in physiologic function, such as baroreceptor sensitivity, often seen with aging. Orthostatic hypotension is a fall in blood pressure on assuming an upright position. Absolute cutoffs for the drop in blood pressure are often difficult to determine because different patients exhibit varying degrees of tolerance to falls in blood pressure. Therefore, strict numerical criteria may lead to underdiagnosis and improper intervention. A thorough review of patient symptomatology combined with appropriate clinical tests should be employed to narrow the vast differential diagnosis and pinpoint the etiology. The fall in blood pressure seen in orthostatic hypotension results from the inability of the autonomic nervous system to adequately compensate for the 500 mL blood that is estimated to pool in the lower extremities on assuming an upright posture. The decrease in venous return results in a concomitant decrease in cardiac output and thus hypoperfusion of the cerebral circulation, possibly resulting in syncope or various other symptoms. A complete investigation should consider hypovolemia, removal of offending medications, primary autonomic disorders, secondary autonomic disorders and, of course, vasovagal syncope, the most common cause of syncope. Although further research is still necessary to rectify the disease process responsible for orthostatic hypotension, patients suffering from this disorder can effectively be treated through a combination of nonpharmacologic treatment, pharmacologic treatment and patient education. Agents such as fludrocortisone, midodrine and erythropoietin show promising results as therapeutic adjuncts. Treatment for recurrent vasovagal syncope includes increased salt intake, and various drug treatments, most of which are still under investigation.
Collapse
Affiliation(s)
- William H Frishman
- Department of Medicine, New York Medical College/Westchester Medical Center, Valhalla, New York 10595, USA.
| | | | | |
Collapse
|