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De Maria B, Dalla Vecchia LA, Bari V, Cairo B, Gelpi F, Perego F, Takahashi ACM, Milan-Mattos JC, Minatel V, Rehder-Santos P, Esler M, Lambert E, Baumert M, Catai AM, Porta A. The degree of engagement of cardiac and sympathetic arms of the baroreflex does not depend on the absolute value and sign of arterial pressure variations. Physiol Meas 2023; 44:114002. [PMID: 37922536 DOI: 10.1088/1361-6579/ad0976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Accepted: 11/03/2023] [Indexed: 11/07/2023]
Abstract
Objective.The percentages of cardiac and sympathetic baroreflex patterns detected via baroreflex sequence (SEQ) technique from spontaneous variability of heart period (HP) and systolic arterial pressure (SAP) and of muscle nerve sympathetic activity (MSNA) burst rate and diastolic arterial pressure (DAP) are utilized to assess the level of the baroreflex engagement. The cardiac baroreflex patterns can be distinguished in those featuring both HP and SAP increases (cSEQ++) and decreases (cSEQ--), while the sympathetic baroreflex patterns in those featuring a MSNA burst rate decrease and a DAP increase (sSEQ+-) and vice versa (sSEQ-+). The present study aims to assess the modifications of the involvement of the cardiac and sympathetic arms of the baroreflex with age and postural stimulus intensity.Approach.We monitored the percentages of cSEQ++ (%cSEQ++) and cSEQ-- (%cSEQ--) in 100 healthy subjects (age: 21-70 years, 54 males, 46 females), divided into five sex-balanced groups consisting of 20 subjects in each decade at rest in supine position and during active standing (STAND). We evaluated %cSEQ++, %cSEQ--, and the percentages of sSEQ+- (%sSEQ+-) and sSEQ-+ (%sSEQ-+) in 12 young healthy subjects (age 23 ± 2 years, 3 females, 9 males) undergoing incremental head-up tilt.Main results.We found that: (i) %cSEQ++ and %cSEQ-- decreased with age and increased with STAND and postural stimulus intensity; (ii) %sSEQ+- and %sSEQ-+ augmented with postural challenge magnitude; (iii) the level of cardiac and sympathetic baroreflex engagement did not depend on either the absolute value of arterial pressure or the direction of its changes.Significance.This study stresses the limited ability of the cardiac and sympathetic arms of the baroreflex in controlling absolute arterial pressure values and the equivalent ability of both positive and negative arterial pressure changes in soliciting them.
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Affiliation(s)
| | | | - Vlasta Bari
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, San Donato Milanese, Milan, Italy
| | - Beatrice Cairo
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | - Francesca Gelpi
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | | | | | | | - Vinicius Minatel
- Department of Physical Therapy, Federal University of São Carlos, São Carlos, Brazil
| | | | - Murray Esler
- Human Neurotransmitters Laboratory, Baker Heart and Diabetes Institute, Melbourne, Australia
| | - Elisabeth Lambert
- School of Health Science, Iverson Health Innovation Research Institute, Swinburne University of Technology, Hawthorn, Australia
| | - Mathias Baumert
- Discipline of Biomedical Engineering, School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, Australia
| | - Aparecida Maria Catai
- Department of Physical Therapy, Federal University of São Carlos, São Carlos, Brazil
| | - Alberto Porta
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, San Donato Milanese, Milan, Italy
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Meglič B, Danieli A. Glyceryl trinitrate-induced blood pressure variability decrease during head-up tilt test predicts vasovagal response. Blood Press Monit 2023; 28:236-243. [PMID: 37334541 DOI: 10.1097/mbp.0000000000000653] [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: 06/20/2023]
Abstract
PURPOSE Glyceryl trinitrate (GTN) provoked cardioinhibitory syncope during the head-up tilt test is preceded by a period of disrupted blood pressure variability (BPV). Endogenous nitric oxide (NO) attenuates BPV independently of blood pressure (BP). We hypothesized that exogenous NO donor GTN might decrease BPV during the presyncope period. A decrease in BPV may predict the tilt outcome. METHODS We analyzed 29 tilt test recordings of subjects with GTN-induced cardioinhibitory syncope and 30 recordings of negative subjects. A recursive autoregressive model of BPV after GTN was performed; powers of the respiratory (0.15-0.45 Hz) and nonrespiratory frequency (0.01-0.15 Hz) bands were calculated for each of the 20 normalized time periods. The post-GTN relative changes in heart rate, BP, and BPV were calculated. RESULTS In the syncope group, spectral power of nonrespiratory frequency systolic and diastolic BPV progressively felt for 30% after GTN application and stabilized after 180 s. BP started to fall 240 s after the GTN application. Decrease in nonrespiratory frequency power of diastolic BPV 20 s after GTN administration predicted cardioinhibitory syncope (area under the curve 0.811; 77% sensitivity; 70% specificity; cutoff value > 7%). CONCLUSION GTN application during the tilt test attenuates systolic and diastolic nonrespiratory frequency BPV during the presyncope period, independent of BP. A decrease in nonrespiratory frequency diastolic BPV 20 s after GTN application predicts cardioinhibitory syncope with good sensitivity and moderate specificity.
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Affiliation(s)
- Bernard Meglič
- Department of Neurology, University Medical Center Ljubljana, Ljubljana, Slovenia
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Moore JP, Simpson LL, Drinkhill MJ. Differential contributions of cardiac, coronary and pulmonary artery vagal mechanoreceptors to reflex control of the circulation. J Physiol 2022; 600:4069-4087. [PMID: 35903901 PMCID: PMC9544715 DOI: 10.1113/jp282305] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Accepted: 07/19/2022] [Indexed: 11/25/2022] Open
Abstract
Distinct populations of stretch-sensitive mechanoreceptors attached to myelinated vagal afferents are found in the heart and adjoining coronary and pulmonary circulations. Receptors at atrio-venous junctions appear to be involved in control of intravascular volume. These atrial receptors influence sympathetic control of the heart and kidney, but contribute little to reflex control of systemic vascular resistance. Baroreceptors at the origins of the coronary circulation elicit reflex vasodilatation, like feedback control from systemic arterial baroreceptors, as well as having characteristics that could contribute to regulation of mean pressure. In contrast, feedback from baroreceptors in the pulmonary artery and bifurcation is excitatory and elicits a pressor response. Elevation of pulmonary arterial pressure resets the vasomotor limb of the systemic arterial baroreflex, which could be relevant for control of sympathetic vasoconstrictor outflow during exercise and other states associated with elevated pulmonary arterial pressure. Ventricular receptors, situated mainly in the inferior posterior wall of the left ventricle, and attached to unmyelinated vagal afferents, are relatively inactive under basal conditions. However, a change to the biochemical environment of cardiac tissue surrounding these receptors elicits a depressor response. Some ventricular receptors respond, modestly, to mechanical distortion. Probably, ventricular receptors contribute little to tonic feedback control; however, reflex bradycardia and hypotension in response to chemical activation may decrease the work of the heart during myocardial ischaemia. Overall, greater awareness of heterogeneous reflex effects originating from cardiac, coronary and pulmonary artery mechanoreceptors is required for a better understanding of integrated neural control of circulatory function and arterial blood pressure.
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Affiliation(s)
| | - Lydia L. Simpson
- Department of Sport ScienceUniversity of InnsbruckInnsbruckAustria
| | - Mark J. Drinkhill
- Leeds Insititute for Cardiovascular and Metabolic MedicineUniversity of LeedsLeedsUK
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Borovik AS, Orlova EA, Tomilovskaya ES, Tarasova OS, Vinogradova OL. Phase Coupling Between Baroreflex Oscillations of Blood Pressure and Heart Rate Changes in 21-Day Dry Immersion. Front Physiol 2020; 11:455. [PMID: 32508675 PMCID: PMC7253653 DOI: 10.3389/fphys.2020.00455] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 04/09/2020] [Indexed: 11/13/2022] Open
Abstract
Introduction Dry immersion (DI) is a ground-based experimental model which reproduces the effects of microgravity on the cardiovascular system and, therefore, can be used to study the mechanisms of post-flight orthostatic intolerance in cosmonauts. However, the effects of long-duration DI on cardiovascular system have not been studied yet. The aim of this work was to study the effects of 21-day DI on systemic hemodynamics and its baroreflex control at rest and during head-up tilt test (HUTT). Methods Ten healthy young men were exposed to DI for 21 days. The day before, on the 7th, 14th, and 19th day of DI, as well as on the 1st and 5th days of recovery they were subjected to HUTT: 15 min in supine position and then 15 min of orthostasis (60°). ECG, arterial pressure, stroke volume and respiration rate were continuously recorded during the test. Phase synchronization index (PSI) of beat-to-beat mean arterial pressure (MAP) and heart rate (HR) in the frequency band of baroreflex waves (∼0.1 Hz) was used as a quantitative measure of baroreflex activity. Results During DI, strong tachycardia and the reduction of stroke volume were observed both in supine position and during HUTT, these indicators did not recover on post-immersion day 5. In contrast, systolic arterial pressure and MAP decreased during HUTT on 14th day of DI, but then restored to pre-immersion values. Before DI and on day 5 of recovery, a transition from supine position to orthostasis was accompanied by an increase in PSI at the baroreflex frequency. However, PSI did not change in HUTT performed during DI and on post-immersion day 1. The amplitude of MAP oscillations at this frequency were increased by HUTT at all time points, while an increase of respective HR oscillations was absent during DI. Conclusion 21-day DI drastically changed the hemodynamic response to HUTT, while its effect on blood pressure was reduced between days 14 and 19, which speaks in favor of the adaptation to the conditions of DI. The lack of increase in phase synchronization of baroreflex MAP and HR oscillations during HUTT indicates disorders of baroreflex cardiac control during DI.
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Affiliation(s)
- Anatoly S Borovik
- State Research Center of the Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia
| | - Evgeniya A Orlova
- State Research Center of the Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia
| | - Elena S Tomilovskaya
- State Research Center of the Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia
| | - Olga S Tarasova
- State Research Center of the Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia.,Faculty of Biology, M.V. Lomonosov Moscow State University, Moscow, Russia
| | - Olga L Vinogradova
- State Research Center of the Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia.,Faculty of Basic Medicine, M.V. Lomonosov Moscow State University, Moscow, Russia
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Hori S, Kamijo YI, Yuzaki M, Kawabe T, Minami K, Umemoto Y, Yokoyama M, Uenishi H, Nishimura Y, Kouda K, Mikami Y, Tajima F. Effect of coronary artery bypass grafting on blood pressure response to head-up tilting. J Physiol Sci 2020; 70:21. [PMID: 32228438 PMCID: PMC7105421 DOI: 10.1186/s12576-020-00746-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 03/11/2020] [Indexed: 12/11/2022]
Abstract
Blood pressure response to head-up tilt (HUT) in 7 healthy subjects and 9 patients before and after coronary artery bypass grafting (CABG) was measured during supine and 15-min 60° HUT. Stroke volume (SV) and ejection fraction (EF) were assessed by echocardiography. Baseline mean arterial pressure (MAP) and heart rate (HR) in patients before CABG were similar to healthy subjects. MAP in patients decreased by 6 (4-9) mmHg [median (1st-3rd quartiles)] during 7-12 mmHg of HUT with decreased cardiac output (CO = SV × HR) while HR remained unchanged. MAP in healthy subjects remained unchanged during HUT with increased HR. Body weight decreased by 3.5 (2.5-3.7) kg and MAP decreased by 6 (2-13) mmHg during the last 3-min HUT while HR increased after CABG. Decreases in SV and CO during HUT disappeared after CABG. Blood pressure decreased during HUT in patients before and after CABG regardless of HR response.
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Affiliation(s)
- Shinnosuke Hori
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Yoshi-Ichiro Kamijo
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan.
| | - Mitsuru Yuzaki
- Department of Thoracic and Cardiovascular Surgery, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Tetsuya Kawabe
- Department of Center for Educational Research and Development, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Kohei Minami
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Yasunori Umemoto
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Mao Yokoyama
- Department of Cardiovascular Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Hiroyasu Uenishi
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Yoshiharu Nishimura
- Department of Thoracic and Cardiovascular Surgery, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Ken Kouda
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Yukio Mikami
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
| | - Fumihiro Tajima
- Department of Rehabilitation Medicine, Wakayama Medical University, School of Medicine, 811-1 Kimiidera, Wakayama, 641-8509, Japan
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Cardiac and Vascular Sympathetic Baroreflex Control during Orthostatic Pre-Syncope. J Clin Med 2019; 8:jcm8091434. [PMID: 31510103 PMCID: PMC6781174 DOI: 10.3390/jcm8091434] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 09/04/2019] [Accepted: 09/05/2019] [Indexed: 11/17/2022] Open
Abstract
We hypothesized that sympathetic baroreflex mediated uncoupling between neural sympathetic discharge pattern and arterial pressure (AP) fluctuations at 0.1 Hz during baroreceptor unloading might promote orthostatic pre-syncope. Ten volunteers (32 ± 6 years) underwent electrocardiogram, beat-to-beat AP, respiratory activity and muscle sympathetic nerve activity (MSNA) recordings while supine (REST) and during 80° head-up tilt (HUT) followed by -10 mmHg stepwise increase of lower body negative pressure until pre-syncope. Cardiac and sympathetic baroreflex sensitivity were quantified. Spectrum analysis of systolic and diastolic AP (SAP and DAP) and calibrated MSNA (cMSNA) variability assessed the low frequency fluctuations (LF, ~0.1 Hz) of SAP, DAP and cMSNA variability. The squared coherence function (K2) quantified the coupling between cMSNA and DAP in the LF band. Analyses were performed while supine, during asymptomatic HUT (T1) and at pre-syncope onset (T2). During T2 we found that: (1) sympathetic baroreceptor modulation was virtually abolished compared to T1; (2) a progressive decrease in AP was accompanied by a persistent but chaotic sympathetic firing; (3) coupling between cMSNA and AP series at 0.1 Hz was reduced compared to T1. A negligible sympathetic baroreceptor modulation during pre-syncope might disrupt sympathetic discharge pattern impairing the capability of vessels to constrict and promote pre-syncope.
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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: 88] [Impact Index Per Article: 12.6] [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.
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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
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Lanfranconi F, Pollastri L, Corna G, Bartesaghi M, Novarina M, Ferri A, Miserocchi GA. The Elusive Path of Brain Tissue Oxygenation and Cerebral Perfusion in Harness Hang Syncope in Mountain Climbers. High Alt Med Biol 2017; 18:363-371. [PMID: 28981369 DOI: 10.1089/ham.2017.0028] [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] [Indexed: 02/07/2023] Open
Abstract
Lanfranconi, Francesca, Luca Pollastri, Giovanni Corna, Manuela Bartesaghi, Massimiliano Novarina, Alessandra Ferri, and Giuseppe Andrea Miserocchi. The elusive path of brain tissue oxygenation and cerebral perfusion in harness hang syncope in mountain climbers. High Alt Med Biol. 18:363-371, 2017. AIM Harness hang syncope (HHS) is a risk that specifically affects wide ranges of situations requiring safety harnesses in mountains. An irreversible orthostatic stasis could lead to death if a prompt rescue is not performed. We aimed at evaluating the risk of developing HHS and at identifying the characteristics related to the pathogenesis of HHS. RESULTS Forty adults (aged 39.1 [8.2] years) were enrolled in a suspension test lasting about 28.7 (11.4) minutes. We measured cardiovascular parameters, and near infrared spectroscopy (NIRS) was used to assess cerebral hypoxia by changes in the concentration of oxyhemoglobin (Δ[HbO2]) and de-oxyhemoglobin (Δ[HHb]). In the four participants who developed HHS: (1) systolic and diastolic blood pressure showed ample oscillations with a final abrupt drop (∼30 mmHg); (2) Δ[HbO2] increased after 8-12 minutes of suspension and reached a plateau before HHS; and (3) Δ[HHb] decreased with a final abrupt increase before syncope. CONCLUSIONS Participants who developed HHS failed to activate cardiovascular reflexes that usually safeguard O2 availability to match the metabolic needs of the brain tissue. Since cerebral hypoxia was detected as an early phenomenon by Δ[HbO2] and Δ[HHb] changes, NIRS measurement appears to be the most important parameter to monitor the onset of HHS.
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Affiliation(s)
- Francesca Lanfranconi
- 1 Laboratory of Clinical Physiology and Sport Medicine, School of Medicine and Surgery, University of Milano-Bicocca , Monza, Italy
| | | | - Giovanni Corna
- 1 Laboratory of Clinical Physiology and Sport Medicine, School of Medicine and Surgery, University of Milano-Bicocca , Monza, Italy
| | | | | | - Alessandra Ferri
- 1 Laboratory of Clinical Physiology and Sport Medicine, School of Medicine and Surgery, University of Milano-Bicocca , Monza, Italy .,3 Clinical Exercise Science Research Program, Institute of Sport Exercise and Active Living (ISEAL), Victoria University , Melbourne, Australia
| | - Giuseppe Andrea Miserocchi
- 1 Laboratory of Clinical Physiology and Sport Medicine, School of Medicine and Surgery, University of Milano-Bicocca , Monza, Italy
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Marchi A, Bari V, De Maria B, Cerutti S, Heusser K, Tank J, Jordan J, Barbic F, Furlan R, Porta A. Evaluation of the correlation between cardiac and sympathetic baroreflex sensitivity before orthostatic syncope. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:2063-6. [PMID: 26736693 DOI: 10.1109/embc.2015.7318793] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The study investigates the two different aspects of the baroreflex control resulting in two baroreflex sensitivity (BRS) indexes: i) sympathetic BRS (sBRS); ii) cardiac BRS (cBRS). sBRS was assessed as the slope of the regression line of the conditional probability of detecting a burst on the integrated muscle nerve sympathetic activity (MSNA) given an assigned diastolic arterial pressure (DAP) on DAP. cBRS was estimated from spontaneous heart period (HP) and systolic arterial pressure (SAP) via a spectral approach in the low (0.04-0-15 Hz) and high (0.15-0.5 Hz) frequency bands respectively. Both sBRS and cBRS were assessed in eight healthy subjects undergoing three experimental sessions: supine resting position (REST), 80 degrees head-up tilt test (TILT) and before the occurrence of pre-syncope symptoms (TILT_PRE). Results showed a decrease of both sBRS and cBRS during TILT and a baroreflex impairment during TILT_PRE. sBRS and cBRS were linearly correlated during TILT but became uncorrelated during TILT_PRE. Findings suggest a failure of both "baroreflexes" and their disassociation during TILT_PRE.
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Iwase S, Nishimura N, Mano T. Role of sympathetic nerve activity in the process of fainting. Front Physiol 2014; 5:343. [PMID: 25309444 PMCID: PMC4164098 DOI: 10.3389/fphys.2014.00343] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Accepted: 08/22/2014] [Indexed: 12/03/2022] Open
Abstract
Syncope is defined as a transient loss of consciousness and postural tone, characterized by rapid onset, short duration, and spontaneous recovery, and the process of syncope progression is here described with two types of sympathetic change. Simultaneous recordings of microneurographically-recorded muscle sympathetic nerve activity (MSNA) and continuous and noninvasive blood pressure measurement has disclosed what is going on during the course of syncope progression. For vasovagal or neurally mediated syncope, three stages are identified in the course of syncope onset, oscillation, imbalance, and catastrophe phases. Vasovagal syncope is characterized by sympathoexcitation, followed by vagal overcoming via the Bezold-Jarisch reflex. Orthostatic syncope is caused by response failure or a lack of sympathetic nerve activity to the orthostatic challenge, followed by fluid shift and subsequent low cerebral perfusion. Four causes are considered for the compensatory failure that triggers orthostatic syncope: hypovolemia, increased pooling in the lower body, failure to activate sympathetic activity, and failure of vasoconstriction against sympathetic vasoconstrictive stimulation. Many pathophysiological conditions have been described from the perspectives of (1) exaggerated sympathoexcitation and (2) failure to activate the sympathetic nerve. We conclude that the sympathetic nervous system can control cardiovascular function, and its failure results in syncope; however, responses of the system obtained by microneurographically-recorded MSNA would determine the pathophysiology of the onset and progression of syncope, explaining the treatment effect that could be achieved by the analysis of this mechanism.
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Affiliation(s)
- Satoshi Iwase
- Department of Physiology, School of Medicine, Aichi Medical University Nagakute, Japan
| | - Naoki Nishimura
- Department of Physiology, School of Medicine, Aichi Medical University Nagakute, Japan
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Sandberg F, Bailón R, Hernando D, Laguna P, Martínez JP, Solem K, Sörnmo L. Prediction of hypotension in hemodialysis patients. Physiol Meas 2014; 35:1885-98. [DOI: 10.1088/0967-3334/35/9/1885] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Pathophysiology of neurally mediated syncope: Role of cardiac output and total peripheral resistance. Auton Neurosci 2014; 184:24-6. [PMID: 25081417 DOI: 10.1016/j.autneu.2014.07.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 07/07/2014] [Accepted: 07/09/2014] [Indexed: 11/24/2022]
Abstract
Syncope is a common clinical condition occurring even in otherwise healthy people without underlying cardiovascular disease. Neurally mediated syncope is by far the most common cause of syncope in individuals without any structural heart disease. Based on traditional wisdom, loss of sympathetic tone with relaxation of vascular smooth muscle is the key mechanism underlying the pathophysiology of syncope, especially in patients without an acute decrease in heart rate. However, this concept has recently been challenged. Some microneurographic studies indicate that sympathetic withdrawal may not always be a prerequisite even for the development of classic "vasodepressor" forms of syncope. Conversely, a decrease in cardiac output appears to be a determinant factor for syncope in most circumstances. This article reviews the relative contribution of cardiac output versus sympathetic vasoconstriction in neurally mediated syncope in otherwise healthy individuals. It is suggested that a moderate to severe fall in cardiac output with or without vasodilatation may contribute to syncope.
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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: 28] [Impact Index Per Article: 2.8] [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.
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Affiliation(s)
- Andrew T Del Pozzi
- Center for Hypotension, 19 Bradhurst Ave, Suite 1600 S, Hawthorne, NY 10532.
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