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Young DA, Jones PAT, Matenchuk BA, Sivak A, Davenport MH, Steinback CD. The effect of hyperoxia on muscle sympathetic nerve activity: a systematic review and meta-analysis. Clin Auton Res 2024; 34:233-252. [PMID: 38709357 DOI: 10.1007/s10286-024-01033-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2024] [Accepted: 04/09/2024] [Indexed: 05/07/2024]
Abstract
PURPOSE We conducted a meta-analysis to determine the effect of hyperoxia on muscle sympathetic nerve activity in healthy individuals and those with cardio-metabolic diseases. METHODS A comprehensive search of electronic databases was performed until August 2022. All study designs (except reviews) were included: population (humans; apparently healthy or with at least one chronic disease); exposures (muscle sympathetic nerve activity during hyperoxia or hyperbaria); comparators (hyperoxia or hyperbaria vs. normoxia); and outcomes (muscle sympathetic nerve activity, heart rate, blood pressure, minute ventilation). Forty-nine studies were ultimately included in the meta-analysis. RESULTS In healthy individuals, hyperoxia had no effect on sympathetic burst frequency (mean difference [MD] - 1.07 bursts/min; 95% confidence interval [CI] - 2.17, 0.04bursts/min; P = 0.06), burst incidence (MD 0.27 bursts/100 heartbeats [hb]; 95% CI - 2.10, 2.64 bursts/100 hb; P = 0.82), burst amplitude (P = 0.85), or total activity (P = 0.31). In those with chronic diseases, hyperoxia decreased burst frequency (MD - 5.57 bursts/min; 95% CI - 7.48, - 3.67 bursts/min; P < 0.001) and burst incidence (MD - 4.44 bursts/100 hb; 95% CI - 7.94, - 0.94 bursts/100 hb; P = 0.01), but had no effect on burst amplitude (P = 0.36) or total activity (P = 0.90). Our meta-regression analyses identified an inverse relationship between normoxic burst frequency and change in burst frequency with hyperoxia. In both groups, hyperoxia decreased heart rate but had no effect on any measure of blood pressure. CONCLUSION Hyperoxia does not change sympathetic activity in healthy humans. Conversely, in those with chronic diseases, hyperoxia decreases sympathetic activity. Regardless of disease status, resting sympathetic burst frequency predicts the degree of change in burst frequency, with larger decreases for those with higher resting activity.
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Affiliation(s)
- Desmond A Young
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Paris A T Jones
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
| | - Brittany A Matenchuk
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
- Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport, and Recreation, Women and Children's Health Research Institute, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Allison Sivak
- Geoffrey and Robyn Sperber Health Sciences Library, University of Alberta, Edmonton, AB, Canada
| | - Margie H Davenport
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada
- Program for Pregnancy and Postpartum Health, Faculty of Kinesiology, Sport, and Recreation, Women and Children's Health Research Institute, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Craig D Steinback
- Neurovascular Health Lab, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, AB, Canada.
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Delliaux S, Ichinose M, Watanabe K, Fujii N, Nishiyasu T. Muscle metaboreflex activation during hypercapnia modifies nonlinear heart rhythm dynamics, increasing the complexity of the sinus node autonomic regulation in humans. Pflugers Arch 2023; 475:527-539. [PMID: 36645512 DOI: 10.1007/s00424-022-02780-x] [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: 10/18/2022] [Revised: 12/01/2022] [Accepted: 12/04/2022] [Indexed: 01/17/2023]
Abstract
Muscle metaboreflex activation during hypercapnia leads to enhanced pressive effects that are poorly understood while autonomic responses including baroreflex function are not documented. Thus, we assessed heart rate variability (HRV) that is partly due to autonomic influences on sinus node with linear tools (spectral analysis of instantaneous heart period), baroreflex set point and sensitivity with the heart period-arterial pressure transfer function and sequences methods, and system coupling through the complexity of RR interval dynamics with nonlinear tools (Poincaré plots and approximate entropy (ApEn)). We studied ten healthy young men at rest and then during muscle metaboreflex activation (MMA, postexercise muscle ischemia) and hypercapnia (HCA, PetCO2 = + 10 mmHg from baseline) separately and combined (MMA + HCA). The strongest pressive responses were observed during MMA + HCA, while baroreflex sensitivity was similarly lowered in the three experimental conditions. HRV was significantly different in MMA + HCA compared to MMA and HCA separately, with the lowest total power spectrum (p < 0.05), including very low frequency (p < 0.05), low frequency (p < 0.05), and high frequency (tendency) power spectra decreases, and the lowest Poincaré plot short-term variability index (SD1): SD1 = 36.2 ms (MMA + HCA) vs. SD1 = 43.1 ms (MMA, p < 0.05) and SD1 = 46.1 ms (HCA, p < 0.05). Moreover, RR interval dynamic complexity was significantly increased only in the MMA + HCA condition (ApEn increased from 1.04 ± 0.04, 1.07 ± 0.02, and 1.05 ± 0.03 to 1.10 ± 0.03, 1.13 ± 0.04, and 1.17 ± 0.03 in MMA, HCA, and MMA + HCA conditions, respectively; p < 0.01). These results suggest that in healthy young men, muscle metaboreflex activation during hypercapnia leads to interactions that reduce parasympathetic influence on the sinus node activity but complexify its dynamics.
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Affiliation(s)
- Stephane Delliaux
- Aix Marseille Univ, INSERM, INRAE, C2VN, Marseille, France.
- Assistance Publique - Hôpitaux de Marseille, APHM, Hôpital Nord, Pôle Cardiovasculaire et Thoracique, Laboratoire de Physiologie Respiratoire - Explorations à l'Exercice, Marseille, France.
- Laboratory of Physiology - Circulation, Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan.
- Japan Society for the Promotion of Science, Tokyo, Japan.
| | - Masashi Ichinose
- Laboratory of Physiology - Circulation, Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
- School of Business and Administration, Meiji University, Tokyo, Japan
| | - Kazuhito Watanabe
- Laboratory of Physiology - Circulation, Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
| | - Naoto Fujii
- Laboratory of Physiology - Circulation, Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
- Japan Society for the Promotion of Science, Tokyo, Japan
| | - Takeshi Nishiyasu
- Laboratory of Physiology - Circulation, Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Japan
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Assessment of Baroreflex Sensitivity Using Time-Frequency Analysis during Postural Change and Hypercapnia. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2019; 2019:4875231. [PMID: 30863454 PMCID: PMC6377966 DOI: 10.1155/2019/4875231] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Revised: 12/16/2018] [Accepted: 01/06/2019] [Indexed: 01/09/2023]
Abstract
Baroreflex is a mechanism of short-term neural control responsible for maintaining stable levels of arterial blood pressure (ABP) in an ABP-heart rate negative feedback loop. Its function is assessed by baroreflex sensitivity (BRS)—a parameter which quantifies the relationship between changes in ABP and corresponding changes in heart rate (HR). The effect of postural change as well as the effect of changes in blood O2 and CO2 have been the focus of multiple previous studies on BRS. However, little is known about the influence of the combination of these two factors on dynamic baroreflex response. Furthermore, classical methods used for BRS assessment are based on the assumption of stationarity that may lead to unreliable results in the case of mostly nonstationary cardiovascular signals. Therefore, we aimed to investigate BRS during repeated transitions between squatting and standing in normal end-tidal CO2 (EtCO2) conditions (normocapnia) and conditions of progressively increasing EtCO2 with a decreasing level of O2 (hypercapnia with hypoxia) using joint time and frequency domain (TF) approach to BRS estimation that overcomes the limitation of classical methods. Noninvasive continuous measurements of ABP and EtCO2 were conducted in a group of 40 healthy young volunteers. The time course of BRS was estimated from TF representations of pulse interval variability and systolic pressure variability, their coherence, and phase spectra. The relationship between time-variant BRS and indices of ABP and HR was analyzed during postural change in normocapnia and hypercapnia with hypoxia. In normocapnia, observed trends in all measures were in accordance with previous studies, supporting the validity of presented TF method. Similar but slightly attenuated response to postural change was observed in hypercapnia with hypoxia. Our results show the merits of the nonstationary methods as a tool to study the cardiovascular system during short-term hemodynamic changes.
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Saku K, Tohyama T, Shinoda M, Kishi T, Hosokawa K, Nishikawa T, Oga Y, Sakamoto T, Tsutsui H, Miyamoto T, Sunagawa K. Central chemoreflex activation induces sympatho-excitation without altering static or dynamic baroreflex function in normal rats. Physiol Rep 2017; 5:5/17/e13406. [PMID: 28899913 PMCID: PMC5599864 DOI: 10.14814/phy2.13406] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 08/07/2017] [Indexed: 11/24/2022] Open
Abstract
Central chemoreflex activation induces sympatho-excitation. However, how central chemoreflex interacts with baroreflex function remains unknown. This study aimed to examine the impact of central chemoreflex on the dynamic as well as static baroreflex functions under open-loop conditions. In 15 anesthetized, vagotomized Sprague-Dawley rats, we isolated bilateral carotid sinuses and controlled intra-sinus pressure (CSP). We then recorded sympathetic nerve activity (SNA) at the celiac ganglia, and activated central chemoreflex by a gas mixture containing various concentrations of CO2 Under the baroreflex open-loop condition (CSP = 100 mmHg), central chemoreflex activation linearly increased SNA and arterial pressure (AP). To examine the static baroreflex function, we increased CSP stepwise from 60 to 170 mmHg and measured steady-state SNA responses to CSP (mechanoneural arc), and AP responses to SNA (neuromechanical arc). Central chemoreflex activation by inhaling 3% CO2 significantly increased SNA irrespective of CSP, indicating resetting of the mechanoneural arc, but did not change the neuromechanical arc. As a result, central chemoreflex activation did not change baroreflex maximum total loop gain significantly (-1.29 ± 0.27 vs. -1.68 ± 0.74, N.S.). To examine the dynamic baroreflex function, we randomly perturbed CSP and estimated transfer functions from 0.01 to 1.0 Hz. The transfer function of the mechanoneural arc approximated a high-pass filter, while those of the neuromechanical arc and total (CSP-AP relationship) arcs approximated a low-pass filter. In conclusion, central chemoreflex activation did not alter the transfer function of the mechanoneural, neuromechanical, or total arcs. Central chemoreflex modifies hemodynamics via sympatho-excitation without compromising dynamic or static baroreflex AP buffering function.
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Affiliation(s)
- Keita Saku
- Department of Advanced Risk Stratification for Cardiovascular Diseases, Center for Disruptive Cardiovascular Medicine, Kyushu University, Fukuoka, Japan
| | - Takeshi Tohyama
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Masako Shinoda
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Takuya Kishi
- Department of Advanced Risk Stratification for Cardiovascular Diseases, Center for Disruptive Cardiovascular Medicine, Kyushu University, Fukuoka, Japan
| | - Kazuya Hosokawa
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Takuya Nishikawa
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Yasuhiro Oga
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Takafumi Sakamoto
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Hiroyuki Tsutsui
- Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan
| | - Tadayoshi Miyamoto
- Graduate School of Health Sciences, Morinomiya University of Medical Sciences, Osaka, Japan
| | - Kenji Sunagawa
- Department of Therapeutic Regulation of Cardiovascular Homeostasis, Center for Disruptive Cardiovascular Medicine Kyushu University, Fukuoka, Japan
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Brothers RM, Lucas RAI, Zhu YS, Crandall CG, Zhang R. Cerebral vasomotor reactivity: steady-state versus transient changes in carbon dioxide tension. Exp Physiol 2014; 99:1499-510. [PMID: 25172891 PMCID: PMC4218865 DOI: 10.1113/expphysiol.2014.081190] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
New Findings What is the central question of this study? The relationship between changes in cerebral blood flow and arterial carbon dioxide tension is used to assess cerebrovascular function. Hypercapnia is generally evoked by two methods, i.e. steady-state and transient increases in carbon dioxide tension. In some cases, the hypercapnia is immediately preceded by a period of hypocapnia. It is unknown whether the cerebrovascular response differs between these methods and whether a period of hypocapnia blunts the subsequent response to hypercapnia. What is the main finding and its importance? The cerebrovascular response is similar between steady-state and transient hypercapnia. However, hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.
Cerebral vasomotor reactivity (CVMR) to changes in arterial carbon dioxide tension () is assessed during steady-state or transient changes in . This study tested the following two hypotheses: (i) that CVMR during steady-state changes differs from that during transient changes in ; and (ii) that CVMR during rebreathing-induced hypercapnia would be blunted when preceded by a period of hyperventilation. For each hypothesis, end-tidal carbon dioxide tension () middle cerebral artery blood velocity (CBFV), cerebrovascular conductance index (CVCI; CBFV/mean arterial pressure) and CVMR (slope of the linear regression between changes in CBFV and CVCI versus) were assessed in eight individuals. To address the first hypothesis, measurements were made during the following two conditions (randomized): (i) steady-state increases in of 5 and 10 Torr above baseline; and (ii) rebreathing-induced transient breath-by-breath increases in . The linear regression for CBFV versus (P = 0.65) and CVCI versus (P = 0.44) was similar between methods; however, individual variability in CBFV or CVCI responses existed among subjects. To address the second hypothesis, the same measurements were made during the following two conditions (randomized): (i) immediately following a brief period of hypocapnia induced by hyperventilation for 1 min followed by rebreathing; and (ii) during rebreathing only. The slope of the linear regression for CBFV versus (P < 0.01) and CVCI versus (P < 0.01) was reduced during hyperventilation plus rebreathing relative to rebreathing only. These results indicate that cerebral vasomotor reactivity to changes in is similar regardless of the employed methodology to induce changes in and that hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.
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Affiliation(s)
- R Matthew Brothers
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA Department of Kinesiology and Health Education, University of Texas at Austin, TX, USA
| | - Rebekah A I Lucas
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Yong-Sheng Zhu
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Craig G Crandall
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Rong Zhang
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, TX, USA Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX, USA
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Solaiman AZ, Feehan RP, Chabitnoy AM, Leuenberger UA, Monahan KD. Ventilatory responses to chemoreflex stimulation are not enhanced by angiotensin II in healthy humans. Auton Neurosci 2014; 183:72-9. [PMID: 24556416 DOI: 10.1016/j.autneu.2014.01.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Revised: 11/18/2013] [Accepted: 01/16/2014] [Indexed: 10/25/2022]
Abstract
The chemoreflexes exert significant control over respiration and sympathetic outflow. Abnormalities in chemoreflex function may contribute to various disease processes. Based on prior animal studies, we developed the hypothesis that acutely elevating circulating angiotensin II levels into the pathophysiological range increases chemoreflex responsiveness in healthy humans. Eighteen adults were studied before (Pre) and during (Post) low (protocol 1; 2ng/kg/min; n=9) or high (protocol 2; 5ng/kg/min; n=9) dose angiotensin II infusion (study day 1). Chemoreflex responses were quantified by the pure nitrogen breathing method [slope of the minute ventilation vs. arterial oxygen saturation plot generated during a series (n=10) of 100% inspired nitrogen exposures (1-8 breaths)] and by measuring responses to hypercapnia (7% inspired carbon dioxide). Responses to a non-chemoreflex stimulus were also determined (cold pressor test). Measurements were repeated on a subsequent day (study day 2) before and during infusion of a control vasoconstrictor (phenylephrine) infused at a dose (0.6-1.2μg/kg/min) sufficient to increase blood pressure to the same degree as that achieved during angiotensin II infusion. We found that despite increasing plasma angiotensin II levels to pathophysiological levels responses to pure nitrogen breathing, hypercapnia, and the cold pressor test were unchanged by low (2ng/kg/min) and high dose (5ng/kg/min) angiotensin II infusion (protocols 1 and 2). Similarly, responses measured during phenylephrine infusion (Post) were unchanged (from Pre). These findings indicate that acutely increasing plasma angiotensin II levels to levels observed in disease states, such as human heart failure, do not increase chemoreflex responsiveness in healthy humans.
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Affiliation(s)
- Adil Z Solaiman
- Penn State Heart and Vascular Institute, Pennsylvania State University College of Medicine, Hershey, PA 17033, United States
| | - Robert P Feehan
- Penn State Heart and Vascular Institute, Pennsylvania State University College of Medicine, Hershey, PA 17033, United States
| | - Amy M Chabitnoy
- Penn State Heart and Vascular Institute, Pennsylvania State University College of Medicine, Hershey, PA 17033, United States
| | - Urs A Leuenberger
- Penn State Heart and Vascular Institute, Pennsylvania State University College of Medicine, Hershey, PA 17033, United States
| | - Kevin D Monahan
- Penn State Heart and Vascular Institute, Pennsylvania State University College of Medicine, Hershey, PA 17033, United States.
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Phillips AA, Krassioukov AV, Ainslie PN, Warburton DE. Baroreflex Function after Spinal Cord Injury. J Neurotrauma 2012; 29:2431-45. [DOI: 10.1089/neu.2012.2507] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Affiliation(s)
- Aaron A. Phillips
- Cardiovascular Physiology and Rehabilitation Laboratory, Physical Activity Promotion and Chronic Disease Prevention Unit, University of British Columbia, British Columbia, Canada
- Experimental Medicine Program, Faculty of Medicine, University of British Columbia, British Columbia, Canada
- International Collaboration of Repair Discoveries, University of British Columbia, British Columbia, Canada
| | - Andrei V. Krassioukov
- Experimental Medicine Program, Faculty of Medicine, University of British Columbia, British Columbia, Canada
- International Collaboration of Repair Discoveries, University of British Columbia, British Columbia, Canada
- Division of Physical Medicine and Rehabilitation, Department of Medicine, University of British Columbia, British Columbia, Canada
| | - Philip N. Ainslie
- School of Health and Exercise Sciences, Faculty of Health and Social Development, University of British Columbia Okanagan, Kelowna, British Columbia, Canada
| | - Darren E.R. Warburton
- Cardiovascular Physiology and Rehabilitation Laboratory, Physical Activity Promotion and Chronic Disease Prevention Unit, University of British Columbia, British Columbia, Canada
- Experimental Medicine Program, Faculty of Medicine, University of British Columbia, British Columbia, Canada
- International Collaboration of Repair Discoveries, University of British Columbia, British Columbia, Canada
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LEN TREVORK, NEARY JPATRICK, ASMUNDSON GORDONJG, GOODMAN DAVIDG, BJORNSON BRUCE, BHAMBHANI YAGESHN. Cerebrovascular Reactivity Impairment after Sport-Induced Concussion. Med Sci Sports Exerc 2011; 43:2241-8. [DOI: 10.1249/mss.0b013e3182249539] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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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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Pitsikoulis C, Bartels MN, Gates G, Rebmann RA, Layton AM, De Meersman RE. Sympathetic drive is modulated by central chemoreceptor activation. Respir Physiol Neurobiol 2008; 164:373-9. [DOI: 10.1016/j.resp.2008.08.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2008] [Revised: 08/27/2008] [Accepted: 08/29/2008] [Indexed: 11/27/2022]
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Ainslie PN, Celi L, McGrattan K, Peebles K, Ogoh S. Dynamic cerebral autoregulation and baroreflex sensitivity during modest and severe step changes in arterial PCO2. Brain Res 2008; 1230:115-24. [DOI: 10.1016/j.brainres.2008.07.048] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2008] [Revised: 07/10/2008] [Accepted: 07/11/2008] [Indexed: 11/29/2022]
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