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Larson M, Chantigian DP, Asirvatham-Jeyaraj N, Van de Winckel A, Keller-Ross ML. Slow-Paced Breathing and Autonomic Function in People Post-stroke. Front Physiol 2020; 11:573325. [PMID: 33192570 PMCID: PMC7662434 DOI: 10.3389/fphys.2020.573325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 09/28/2020] [Indexed: 11/14/2022] Open
Abstract
Purpose: To determine if acute slow breathing at 6 breaths/min would improve baroreflex sensitivity (BRS) and heart rate variability (HRV), and lower blood pressure (BP) in adults after stroke. Methods: Twelve individuals completed two randomized study visits where they performed a 15-min bout of breathing exercises at 6 breaths/min (slow) and at 12 breaths/min (control). Continuous BP and heart rate (HR) were measured throughout, and BRS, BRS response to elevations in blood pressure (BRSup), BRS response to depressions in blood pressure (BRSdown), and HRV were calculated and analyzed before (pre), during, and after (post) breathing exercises. Results: BRS increased from pre to post slow breathing by 10% (p = 0.012), whereas BRSup increased from pre to during slow breathing by 30% (p = 0.04). BRSdown increased from pre to post breathing for both breathing conditions (p < 0.05). HR (control: Δ - 4 ± 4; slow: Δ - 3 ± 4 beats/min, time, p < 0.01) and systolic BP (control: Δ - 0.5 ± 5; slow: Δ - 6.3 ± 8 mmHg, time, p < 0.01) decreased after both breathing conditions. Total power, low frequency power, and standard deviation of normal inter-beat intervals (SDNN) increased during the 6-breaths/min condition (condition × time, p < 0.001), whereas high frequency increased during both breathing conditions (time effect, p = 0.009). Conclusions: This study demonstrated that in people post-stroke, slow breathing may increase BRS, particularly BRSup, more than a typical breathing space; however, paced breathing at either a slow or typical breathing rate appears to be beneficial for acutely decreasing systolic BP and HR and increasing HRV.
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Affiliation(s)
- Mia Larson
- Division of Rehabilitation Science, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN, United States
| | - Daniel P. Chantigian
- Division of Rehabilitation Science, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN, United States
| | - Ninitha Asirvatham-Jeyaraj
- Indian Institute of Science, Bangalore, India
- Division of Physical Therapy, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN, United States
| | - Ann Van de Winckel
- Division of Rehabilitation Science, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN, United States
- Division of Physical Therapy, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN, United States
| | - Manda L. Keller-Ross
- Division of Rehabilitation Science, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN, United States
- Division of Physical Therapy, Department of Rehabilitation Medicine, Medical School, University of Minnesota, Minneapolis, MN, United States
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De Maria B, Bari V, Cairo B, Vaini E, Martins de Abreu R, Perseguini NM, Milan-Mattos J, Rehder-Santos P, Minatel V, Catai AM, Dalla Vecchia LA, Porta A. Cardiac baroreflex hysteresis is one of the determinants of the heart period variability asymmetry. Am J Physiol Regul Integr Comp Physiol 2019; 317:R539-R551. [PMID: 31365303 DOI: 10.1152/ajpregu.00112.2019] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In heart period (HP) variability (HPV) recordings the percentage of negative HP variations tends to be greater than that of positive ones and this pattern is referred to as HPV asymmetry (HPVA). HPVA has been studied in several experimental conditions in healthy and pathological populations, but its origin is unclear. The baroreflex (BR) exhibits an asymmetric behavior as well given that it reacts more importantly to positive than negative arterial pressure (AP) variations. We tested the hypothesis that the BR asymmetry (BRA) is a HPVA determinant over spontaneous fluctuations of HP and systolic AP (SAP). We studied 100 healthy subjects (age from 21 to 70 yr, 54 men) comprising 20 subjects in each age decade. Electrocardiogram and noninvasive AP were recorded for 15 min at rest in supine position (REST) and during active standing (STAND). The HPVA was evaluated via Porta's index and Guzik's index, while the BRA was assessed as the difference, and normalized difference, between BR sensitivities computed over positive and negative SAP variations via the sequence method applied to HP and SAP variability. HPVA significantly increased during STAND and decreased progressively with age. BRA was not significantly detected both at REST and during STAND. However, we found a significant positive association between BRA and HPVA markers during STAND persisting even within the age groups. This study supports the use of HPVA indexes as descriptors of BRA and identified a challenge soliciting the BR response like STAND to maximize the association between HPVA and BRA markers.
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Affiliation(s)
- Beatrice De Maria
- Istituto di Ricovero e Cura a Carattere Scientifico Istituti Clinici Scientifici Maugeri, Milan, Italy
| | - Vlasta Bari
- Department of Cardiothoracic, Vascular Anesthesia, and Intensive Care, Istituto di Ricovero e Cura a Carattere Scientifico Policlinico San Donato, San Donato Milanese, Milan, Italy
| | - Beatrice Cairo
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | - Emanuele Vaini
- Department of Cardiothoracic, Vascular Anesthesia, and Intensive Care, Istituto di Ricovero e Cura a Carattere Scientifico Policlinico San Donato, San Donato Milanese, Milan, Italy
| | | | | | - Juliana Milan-Mattos
- Department of Physiotherapy, Federal University of São Carlos, São Carlos, São Paulo, Brazil
| | - Patricia Rehder-Santos
- Department of Physiotherapy, Federal University of São Carlos, São Carlos, São Paulo, Brazil
| | - Vinícius Minatel
- Department of Physiotherapy, Federal University of São Carlos, São Carlos, São Paulo, Brazil
| | - Aparecida Maria Catai
- Department of Physiotherapy, Federal University of São Carlos, São Carlos, São Paulo, Brazil
| | | | - Alberto Porta
- Department of Cardiothoracic, Vascular Anesthesia, and Intensive Care, Istituto di Ricovero e Cura a Carattere Scientifico Policlinico San Donato, San Donato Milanese, Milan, Italy.,Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
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Wade TJ, O'Leary DD, Dempster KS, MacNeil AJ, Molnar DS, McGrath J, Cairney J. Adverse childhood experiences (ACEs) and cardiovascular development from childhood to early adulthood: study protocol of the Niagara Longitudinal Heart Study. BMJ Open 2019; 9:e030339. [PMID: 31315878 PMCID: PMC6661634 DOI: 10.1136/bmjopen-2019-030339] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
INTRODUCTION Recent reviews have found substantial links between a toxic childhood environment including child abuse and severe household dysfunction and adult cardiovascular disease (CVD). Collectively referred to as adverse childhood experiences (ACEs), this toxic environment is prevalent among children, with recent Canadian estimates of child abuse at 27%-32%, and severe household dysfunction at 49%. Based on these prevalence rates, the potential effect of ACEs on CVD is more significant than previously thought. Yet, how ACEs amplify the risk for later CVD remains unclear. Lifestyle risk factors only partially account for this connection, instead directing attention to the interaction between psychosocial factors and physiological mechanisms such as inflammation. The Niagara Longitudinal Heart Study (NLHS) examines how ACEs influence cardiovascular health (CVH) from childhood to early adulthood. Integrating the stress process and biological embedding models, this study examines how psychosocial and physiological factors in addition to lifestyle factors explain the relationship between ACEs and CVH. METHODS This follow-up study combines three baseline studies from 2007 to 2012 that collected CVH measures including child blood pressure, heart rate, left ventricular structure and function, arterial stiffness indices and baroreflex sensitivity on 564 children. Baseline data also include anthropometric, biological, lifestyle, behavioural, and psychosocial measures that varied across primary studies. Now over 18 years of age, we will recruit and retest as many participants from the baseline studies as possible collecting data on ACEs, CVH, anthropometric, lifestyle and psychosocial measures as well as blood, saliva and hair for physiological biostress markers. ETHICS AND DISSEMINATION Ethics approval has been received for the NLHS follow-up. Written consent to participate in the follow-up study is obtained from each participant. Results testing all proposed hypotheses will be submitted for publication in peer-reviewed journals.
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Affiliation(s)
- Terrance J Wade
- Health Sciences, Brock University, St. Catharines, Ontario, Canada
- Brock-NIagara Centre for Health and Well-Being, Brock University, St. Catharines, Ontario, Canada
- Child and Youth Studies, Brock University, St. Catharines, Ontario, Canada
| | - Deborah D O'Leary
- Health Sciences, Brock University, St. Catharines, Ontario, Canada
- Brock-NIagara Centre for Health and Well-Being, Brock University, St. Catharines, Ontario, Canada
| | - Kylie S Dempster
- Health Sciences, Brock University, St. Catharines, Ontario, Canada
- Brock-NIagara Centre for Health and Well-Being, Brock University, St. Catharines, Ontario, Canada
| | - Adam J MacNeil
- Health Sciences, Brock University, St. Catharines, Ontario, Canada
| | - Danielle S Molnar
- Child and Youth Studies, Brock University, St. Catharines, Ontario, Canada
| | - Jennifer McGrath
- Department of Psychology, Concordia University, Montreal, Quebec, Canada
| | - John Cairney
- Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, Ontario, Canada
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De Maria B, Bari V, Cairo B, Vaini E, Esler M, Lambert E, Baumert M, Cerutti S, Dalla Vecchia L, Porta A. Characterization of the Asymmetry of the Cardiac and Sympathetic Arms of the Baroreflex From Spontaneous Variability During Incremental Head-Up Tilt. Front Physiol 2019; 10:342. [PMID: 31001137 PMCID: PMC6454064 DOI: 10.3389/fphys.2019.00342] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2018] [Accepted: 03/13/2019] [Indexed: 11/13/2022] Open
Abstract
Hysteresis of the baroreflex (BR) is the result of the different BR sensitivity (BRS) when arterial pressure (AP) rises or falls. This phenomenon has been poorly studied and almost exclusively examined by applying pharmacological challenges and static approaches disregarding causal relations. This study inspects the asymmetry of the cardiac BR (cBR) and vascular sympathetic BR (sBR) in physiological closed loop conditions from spontaneous fluctuations of physiological variables, namely heart period (HP) and systolic AP (SAP) leading to the estimation of cardiac BRS (cBRS) and muscle sympathetic nerve activity (MSNA) and diastolic AP (DAP) leading to the estimation of vascular sympathetic BRS (sBRS). The assessment was carried out in 12 young healthy subjects undergoing incremental head-up tilt with table inclination gradually increased from 0 to 60°. Two analytical methods were exploited and compared, namely the sequence (SEQ) and phase-rectified signal averaging (PRSA) methods. SEQ analysis is based on the detection of joint causal schemes representing the HP and MSNA burst rate delayed responses to spontaneous SAP and DAP modifications, respectively. PRSA analysis averages HP and MSNA burst rate patterns after aligning them according to the direction of SAP and DAP changes, respectively. Since cBRSs were similar when SAP went up or down, hysteresis of cBR was not detected. Conversely, hysteresis of sBR was evident with sBRS more negative when DAP was falling than rising. sBR hysteresis was no longer visible during sympathetic activation induced by the orthostatic challenge. These results were obtained via the SEQ method, while the PRSA technique appeared to be less powerful in describing the BR asymmetry due to the strong association between BRS estimates computed over positive and negative AP variations. This study suggests that cBR and sBR provide different information about the BR control, sBR exhibits more relevant non-linear features that are evident even during physiological changes of AP, and the SEQ method can be fruitfully exploited to characterize the BR hysteresis with promising applications to BR branches different from cBR and sBR.
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Affiliation(s)
| | - Vlasta Bari
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy
| | - Beatrice Cairo
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | - Emanuele Vaini
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy
| | - Murray Esler
- Human Neurotransmitters Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia
| | - Elisabeth Lambert
- Human Neurotransmitters Laboratory, Baker IDI Heart and Diabetes Institute, Melbourne, VIC, Australia.,Faculty of Health, Arts and Design, Iverson Health Innovation Research Institute, Swinburne University of Technology, Hawthorn, VIC, Australia
| | - Mathias Baumert
- School of Electrical and Electronic Engineering, The University of Adelaide, Adelaide, SA, Australia
| | - Sergio Cerutti
- Department of Electronics Information and Bioengineering, Politecnico di Milano, Milan, Italy
| | | | - Alberto Porta
- Department of Cardiothoracic, Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy.,Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
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Horsman HM, Tzeng YC, Galletly DC, Peebles KC. The repeated sit-to-stand maneuver is a superior method for cardiac baroreflex assessment: a comparison with the modified Oxford method and Valsalva maneuver. Am J Physiol Regul Integr Comp Physiol 2014; 307:R1345-52. [DOI: 10.1152/ajpregu.00376.2014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Baroreflex assessment has diagnostic and prognostic utility in the clinical and research environments, and there is a need for a reliable, simple, noninvasive method of assessment. The repeated sit-to-stand method induces oscillatory changes in blood pressure (BP) at a desired frequency and is suitable for assessing dynamic baroreflex sensitivity (BRS). However, little is known about the reliability of this method and its ability to discern fundamental properties of the baroreflex. In this study we sought to: 1) evaluate the reliability of the sit-to-stand method for assessing BRS and compare its performance against two established methods (Oxford method and Valsalva maneuver), and 2) examine whether the frequency of the sit-to-stand method influences hysteresis. Sixteen healthy participants underwent three trials of each method. For the sit-to-stand method, which was performed at 0.1 and 0.05 Hz, BRS was quantified as an integrated response (BRSINT) and in response to falling and rising BP (BRSDOWN and BRSUP, respectively). Test retest reliability was assessed using the intraclass correlation coefficient (ICC). Irrespective of frequency, the ICC for BRSINT during the sit-to-stand method was ≥0.88. The ICC for a rising BP evoked by phenylephrine (PEGAIN) in the Oxford method was 0.78 and ≤0.5 for the remaining measures. During the sit-to-stand method, hysteresis was apparent in all participants at 0.1 Hz but was absent at 0.05 Hz. These findings indicate the sit-to-stand method is a statistically reliable BRS assessment tool and suitable for the examination of baroreflex hysteresis. Using this approach we showed that baroreflex hysteresis is a frequency-dependent phenomenon.
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Affiliation(s)
- H. M. Horsman
- Cardiovascular Systems Laboratory
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
| | - Y. C. Tzeng
- Cardiovascular Systems Laboratory
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
| | - D. C. Galletly
- Cardiovascular Systems Laboratory
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
| | - K. C. Peebles
- Cardiovascular Systems Laboratory
- Centre for Translational Physiology, University of Otago, Wellington, New Zealand
- Department of Physiology, University of Otago, Dunedin, New Zealand; and
- Department of Human Sciences, Macquarie University, Sydney, Australia
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6
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Horsman HM, Peebles KC, Galletly DC, Tzeng YC. Cardiac baroreflex gain is frequency dependent: insights from repeated sit-to-stand maneuvers and the modified Oxford method. Appl Physiol Nutr Metab 2013; 38:753-9. [DOI: 10.1139/apnm-2012-0444] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Helen M. Horsman
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, 23A Mein Street, Wellington South, New Zealand
- Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
| | - Karen C. Peebles
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, 23A Mein Street, Wellington South, New Zealand
- Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
- Department of Physiology, University of Otago, Wellington South, New Zealand
| | - Duncan C. Galletly
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, 23A Mein Street, Wellington South, New Zealand
| | - Yu-Chieh Tzeng
- Cardiovascular Systems Laboratory, Centre for Translational Physiology, University of Otago, 23A Mein Street, Wellington South, New Zealand
- Department of Surgery and Anaesthesia, University of Otago, Wellington South, New Zealand
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Barnes JN, Matzek LJ, Charkoudian N, Joyner MJ, Curry TB, Hart EC. Association of cardiac baroreflex sensitivity with blood pressure transients: influence of sex and menopausal status. Front Physiol 2012; 3:187. [PMID: 22701103 PMCID: PMC3369369 DOI: 10.3389/fphys.2012.00187] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Accepted: 05/21/2012] [Indexed: 11/13/2022] Open
Abstract
The magnitude of decrease in blood pressure (BP) during a vasoactive drug bolus may be associated with the calculated baroreflex sensitivity (BRS). The purpose of the present study was to evaluate whether sympathetic and/or cardiac BRS relates to the extent of change in BP and whether this was altered by sex hormones. Fifty-one young women (27 ± 1 years), 14 older women (58 ± 1 years), and 36 young men (27 ± 1 years) were studied. Heart rate, BP, and muscle sympathetic nerve activity (MSNA) were monitored. Sympathetic BRS was analyzed using the slope of the MSNA-diastolic blood pressure (DBP) relationship and cardiac BRS was analyzed using the R–R interval-systolic blood pressure (SBP) relationship. Young women and men had similar mean arterial pressures (MAP, 91 ± 1 vs. 90 ± 1 mmHg), cardiac BRS (19 ± 1 vs. 21 ± 2 ms/mmHg), and sympathetic BRS (−6 ± 1 vs. −7 ± 1 AU/beat/mmHg), respectively. Older women had higher MAP (104 ± 4 mmHg, p < 0.05) and lower cardiac BRS (7 ± 1 ms/mmHg, p < 0.05), but similar sympathetic BRS (−8 ± 1 AU/beat/mmHg). There was no association between BP transients with either cardiac or sympathetic BRS in young women. In the older women, the drop in SBP, DBP, and MAP were associated with cardiac BRS (r = 0.60, r = 0.59, and r = 0.70, respectively; p < 0.05), but not sympathetic BRS. The decrease in SBP was positively related to cardiac BRS in young men (r = 0.41; p < 0.05). However, there was no relationship between the decrease in BP and sympathetic BRS. This indicates that older women and young men with low cardiac BRS have larger transients in BP during nitroprusside. This suggests a more prominent role for cardiac (as opposed to sympathetic) BRS in responding to acute BP changes in young men and older women. The fact that these relationships do not exist in young women suggest that the female sex hormones influence baroreflex responses.
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Affiliation(s)
- Jill N Barnes
- Human Integrative Physiology Laboratory, Department of Anesthesiology, Mayo Clinic, Rochester MN, USA
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8
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Okada Y, Galbreath MM, Shibata S, Jarvis SS, VanGundy TB, Meier RL, Vongpatanasin W, Levine BD, Fu Q. Relationship between sympathetic baroreflex sensitivity and arterial stiffness in elderly men and women. Hypertension 2011; 59:98-104. [PMID: 22106403 DOI: 10.1161/hypertensionaha.111.176560] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Previous human studies have shown that large-artery stiffness contributes to an age-related decrease in cardiovagal baroreflex sensitivity. Whether this is also true with sympathetic baroreflex sensitivity is unknown. We tested the hypothesis that sympathetic baroreflex sensitivity is associated with the stiffness of baroreceptor segments (the carotid artery and the aorta) in elderly individuals and that sex affects this relationship. Sympathetic baroreflex sensitivity was assessed from the spontaneous changes in beat-by-beat diastolic pressure and corresponding muscle sympathetic nerve activity (microneurography) during supine rest in 30 men (mean±SEM: 69±1 years) and 31 women (68±1 years). Carotid artery stiffness (B-mode ultrasonography) and aortic stiffness (MRI) were also determined. We found that elderly women had lower sympathetic baroreflex sensitivity than elderly men (-2.33±0.25 versus -3.32±0.25 bursts · 100 beats(-1) · mm Hg(-1); P=0.007). β-Stiffness indices of the carotid artery and the aorta were greater in elderly women than in men (6.68±0.48 versus 5.10±0.50 and 4.03±0.47 versus 2.68±0.42; both P<0.050). Sympathetic baroreflex sensitivity was inversely correlated with carotid artery stiffness in both men and women (r=0.49 and 0.50; both P<0.05), whereas this relation was shifted in parallel upward (toward a reduced sensitivity) in women with no changes in the slope (0.26 versus 0.24 arbitrary units). Sympathetic baroreflex sensitivity and aortic stiffness showed similar trends. Thus, barosensory artery stiffness seems to be one independent determinant of sympathetic baroreflex sensitivity in elderly men and women. The lower sympathetic baroreflex sensitivity in elderly women may predispose them to an increased prevalence of hypertension.
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Affiliation(s)
- Yoshiyuki Okada
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas, TX 75231, USA
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9
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Studinger P, Goldstein R, Taylor JA. Age- and fitness-related alterations in vascular sympathetic control. J Physiol 2009; 587:2049-57. [PMID: 19273575 DOI: 10.1113/jphysiol.2009.170134] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In the current study we explored (1) if there were differences in sympathetic activity and baroreflex function by age, sex, or physical activity status, (2) if any aspect of baroreflex function related to differences in resting sympathetic activity, and (3) if mechanical and/or neural baroreflex components related to differences in integrated baroreflex gain. Electrocardiogram, blood pressure, carotid diameter and muscle sympathetic nerve activity were recorded continuously at rest and during sequential bolus injections of sodium nitroprusside and phenylephrine in 22 young, 21 older sedentary and 10 older trained individuals. Analyses of co-variance were used to examine age, sex and training status differences and to explore the explanatory power of integrated baroreflex gain and its mechanical and neural components. Training status and sex influenced neither resting sympathetic outflow nor sympathetic baroreflex gain components. Older subjects had a smaller mechanical component and a strong tendency towards a greater neural component of the sympathetic baroreflex during both pressure falls and pressure rises. Opposing age-related changes in mechanical and neural components resulted in a smaller integrated gain during pressure falls, but a greater integrated gain during pressure rises in older subjects. Thus, in older individuals, compromised sympathetic activation to pressure falls was owing to the stiffening of barosensory vessels, whereas the more sensitive sympathoinhibition to pressure rise was due to an increased neural control. Enhanced neural control with age, however, did not contribute the increased resting sympathetic outflow, which indicates that these two changes are probably driven by distinct neural mechanisms.
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Affiliation(s)
- Péter Studinger
- Department of Physical Medicine and Rehabilitation, Harvard Medical School. Spaulding Rehabilitation Hospital, Boston, MA 02114, USA
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10
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Steinback CD, Salzer D, Medeiros PJ, Kowalchuk J, Shoemaker JK. Hypercapnic vs. hypoxic control of cardiovascular, cardiovagal, and sympathetic function. Am J Physiol Regul Integr Comp Physiol 2008; 296:R402-10. [PMID: 19091913 DOI: 10.1152/ajpregu.90772.2008] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We compared the integrated cardiovascular and autonomic responses to hypercapnia and hypoxia to test the hypothesis that these stimuli differentially affect muscle sympathetic nerve activity (MSNA) discharge patterns and cardiovagal and sympathetic baroreflex function in a manner related to ventilatory chemoreflex sensitivity. Six males and six females underwent 5 min of hypoxia (end-tidal Po2 = 45 Torr) and 5 min of hypercapnia (end-tidal Pco2 = +8 Torr from baseline), causing similar ventilatory responses. A downward right shift in cardiovagal set point was observed during both conditions, which was strongly related to the change in inspiratory time (Ti) from baseline to hypercapnia (r2 = 0.67, P = 0.007) and hypoxia (r2 = 0.79, P < 0.001). Cardiovagal baroreflex gain was decreased during hypoxia (20.1 +/- 6.9 vs. 8.9 +/- 5.1 ms/mmHg, P < 0.001) but not hypercapnia (26.7 +/- 12.7 vs. 23.0 +/- 9.1 ms/mmHg). Both hypoxia and hypercapnia increased MSNA burst amplitude, whereas hypoxia, but not hypercapnia, also increased in MSNA burst frequency (21 +/- 9 vs. 28 +/- 7 bursts/min, P = 0.03) and total MSNA (4.56 +/- 3.07 vs. 7.37 +/- 3.26 mV/min, P = 0.002). However, neither hypercapnia nor hypoxia affected sympathetic burst probability or baroreflex gain. Hypoxia also caused a greater reduction in total peripheral resistance (P = 0.04), a greater increase in heart rate (P = 0.002), and a trend for a greater cardiac output response (P = 0.06) compared with hypercapnia. Nonetheless, central venous pressure remained unchanged during either condition. These results suggest that hypercapnia and hypoxia exert differential effects on cardiovagal, but not sympathetic, baroreflex gain and set point in a manner not related to ventilatory chemoreflex sensitivity. Furthermore, the data suggest that the individual's respiratory pattern to hypoxia or hypercapnia, as reflected in the inspiratory time, was a strong determinant of cardiovagal baroreflex set- point rather than the total ventilatory chemoreflex gain per se.
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Affiliation(s)
- Craig D Steinback
- School of Kinesiology, The University of Western Ontario, London, ON, N6A 3K7, Canada
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11
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Young CN, Fisher JP, Fadel PJ. The ups and downs of assessing baroreflex function. J Physiol 2008; 586:1209-11. [PMID: 18187468 DOI: 10.1113/jphysiol.2007.149484] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Colin N Young
- 1Department ofMedical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA
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12
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Studinger P, Goldstein R, Taylor JA. Mechanical and neural contributions to hysteresis in the cardiac vagal limb of the arterial baroreflex. J Physiol 2007; 583:1041-8. [PMID: 17640929 PMCID: PMC2277195 DOI: 10.1113/jphysiol.2007.139204] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
According to conventional wisdom, hysteresis in cardiac vagal baroreflex function exhibits a specific pattern: pressure falls are associated with longer heart periods and a smaller linear gain. A similar pattern occurs in the pressure-diameter relationship of barosensory vessels, and therefore it has been suggested that baroreflex hysteresis derives solely from vascular behaviour. However, we hypothesized that mechanical and neural baroreflex components contribute equally to baroreflex hysteresis. Blood pressure, carotid diameter and the electrocardiogram were recorded continuously during two trials of sequential bolus injections of nitroprusside and phenylephrine in 14 young healthy subjects. Baroreflex gain and its mechanical and neural components were estimated for falls and rises in pressure and diameter. The position or set point of the relations was quantified at the mean pressure and mean diameter. Gains were determined via piecewise linear regression. Set points and gains for falls versus rises in pressure and diameter were compared with the Chow test. Hysteresis was observed in all individuals, but not in every trial. In most, but not all, trials pressure falls were associated with longer heart periods and smaller linear gain, as conventional wisdom would predict. However, the pattern of hysteresis derived from the interaction of both mechanical and neural components. The two components most often acted in opposition to determine differences in set point, but in conjunction to determine differences in baroreflex gain. Therefore, we conclude that hysteresis is not solely determined by barosensory vessel behaviour but by the complex interaction of mechanical and neural aspects of the arterial baroreflex.
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Affiliation(s)
- Péter Studinger
- Department of Physical Medicine and Rehabilitation, Harvard Medical School, Boston, MA 02114, USA
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