scholarly journals Effect of hypoxia on arterial baroreflex control of heart rate and muscle sympathetic nerve activity in humans

2002 ◽  
Vol 93 (3) ◽  
pp. 857-864 ◽  
Author(s):  
John R. Halliwill ◽  
Christopher T. Minson
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Sympathetic Activity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Acute Hypoxia ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Normotensive Subjects

We tested the hypothesis that acute hypoxia would alter the sensitivity of arterial baroreflex control of both heart rate and sympathetic vasoconstrictor outflow. In 16 healthy, nonsmoking, normotensive subjects (8 women, 8 men, age 20–33 yr), we assessed baroreflex control of heart rate and muscle sympathetic nerve activity by using the modified Oxford technique during both normoxia and hypoxia (12% O2). Compared with normoxia, hypoxia reduced arterial O2 saturation levels from 96.8 ± 0.3 to 80.7 ± 1.4% ( P < 0.001), increased heart rate from 59.8 ± 2.4 to 79.4 ± 2.9 beats/min ( P < 0.001), increased mean arterial pressure from 96.7 ± 2.5 to 105.0 ± 3.3 mmHg ( P = 0.002), and increased sympathetic activity 126 ± 58% ( P < 0.05). The sensitivity for baroreflex control of both heart rate and sympathetic activity was not altered by hypoxia (heart rate: −1.02 ± 0.09 vs. −1.02 ± 0.11 beats · min−1 · mmHg−1; nerve activity: −5.6 ± 0.9 vs. −6.2 ± 0.9 integrated activity · beat−1 · mmHg−1; both P > 0.05). Acute exposure to hypoxia reset baroreflex control of both heart rate and sympathetic activity to higher pressures without changes in baroreflex sensitivity.

Hyperventilation alters arterial baroreflex control of heart rate and muscle sympathetic nerve activity

2000 ◽  
Vol 279 (2) ◽  
pp. H536-H541 ◽  
Author(s):  
Philippe Van de Borne ◽  
Silvia Mezzetti ◽  
Nicola Montano ◽  
Krzysztof Narkiewicz ◽  
Jean Paul Degaute ◽  
...  
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Baroreflex Sensitivity ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Normal Subjects ◽  
Arterial Baroreflex ◽  
Baroreceptor Sensitivity ◽  
Nerve Activity ◽  
Baroreflex Control

Interactions between mechanisms governing ventilation and blood pressure (BP) are not well understood. We studied in 11 resting normal subjects the effects of sustained isocapnic hyperventilation on arterial baroreceptor sensitivity, determined as the α index between oscillations in systolic BP (SBP) generated by respiration and oscillations present in R-R intervals (RR) and in peripheral sympathetic nerve traffic [muscle sympathetic nerve activity (MSNA)]. Tidal volume increased from 478 ± 24 to 1,499 ± 84 ml and raised SBP from 118 ± 2 to 125 ± 3 mmHg, whereas RR decreased from 947 ± 18 to 855 ± 11 ms (all P < 0.0001); MSNA did not change. Hyperventilation reduced arterial baroreflex sensitivity to oscillations in SBP at both cardiac (from 13 ± 1 to 9 ± 1 ms/mmHg, P < 0.001) and MSNA levels (by −37 ± 5%, P < 0.0001). Thus increased BP during hyperventilation does not elicit any reduction in either heart rate or MSNA. Baroreflex modulation of RR and MSNA in response to hyperventilation-induced BP oscillations is attenuated. Blunted baroreflex gain during hyperventilation may be a mechanism that facilitates simultaneous increases in BP, heart rate, and sympathetic activity during dynamic exercise and chemoreceptor activation.

Alterations in sympathetic neurovascular transduction during acute hypoxia in humans

2013 ◽  
Vol 304 (11) ◽  
pp. R959-R965 ◽  
Author(s):  
Can Ozan Tan ◽  
Yu-Chieh Tzeng ◽  
Jason W. Hamner ◽  
Renaud Tamisier ◽  
J. Andrew Taylor
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Sympathetic Activity ◽  
Sympathetic Nerve Activity ◽  
Pressor Response ◽  
Acute Hypoxia ◽  
Sympathetic Outflow ◽  
Isometric Handgrip ◽  
Nerve Activity ◽  
Hypoxic Exercise

Resting vascular sympathetic outflow is significantly increased during and beyond exposure to acute hypoxia without a parallel increase in either resistance or pressure. This uncoupling may indicate a reduction in the ability of sympathetic outflow to effect vascular responses (sympathetic transduction). However, the effect of hypoxia on sympathetic transduction has not been explored. We hypothesized that transduction would either remain unchanged or be reduced by isocapnic hypoxia. In 11 young healthy individuals, we measured beat-by-beat pressure, multiunit sympathetic nerve activity, and popliteal blood flow velocity at rest and during isometric handgrip exercise to fatigue, before and during isocapnic hypoxia (∼80% SpO2), and derived sympathetic transduction for each subject via a transfer function that reflects Poiseuille's law of flow. During hypoxia, heart rate and sympathetic nerve activity increased, whereas pressure and flow remained unchanged. Both normoxic and hypoxic exercise elicited significant increases in heart rate, pressure, and sympathetic activity, although sympathetic responses to hypoxic exercise were blunted. Hypoxia slightly increased the gain relation between pressure and flow (0.062 ± 0.006 vs. 0.074 ± 0.004 cm·s−1·mmHg−1; P = 0.04), but markedly increased sympathetic transduction (−0.024 ± 0.005 vs. −0.042 ± 0.007 cm·s−1·spike−1; P < 0.01). The pressor response to isometric handgrip was similar during normoxic and hypoxic exercise due to the balance of interactions among the tachycardia, sympathoexcitation, and transduction. This indicates that the ability of sympathetic activity to affect vasoconstriction is enhanced during brief exposure to isocapnic hypoxia, and this appears to offset the potent vasodilatory stimulus of hypoxia.

scholarly journals Water drinking enhances the gain of arterial baroreflex control of muscle sympathetic nerve activity in healthy young humans

2018 ◽  
Vol 103 (10) ◽  
pp. 1318-1325 ◽  
Author(s):  
Lauro C. Vianna ◽  
Igor A. Fernandes ◽  
Daniel G. Martinez ◽  
André L. Teixeira ◽  
Bruno M. Silva ◽  
...  
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Water Drinking

scholarly journals Habitual cigarette smoking raises pressor responses to spontaneous bursts of muscle sympathetic nerve activity

2019 ◽  
Vol 317 (2) ◽  
pp. R280-R288 ◽  
Author(s):  
Jian Cui ◽  
Rachel C. Drew ◽  
Matthew D. Muller ◽  
Cheryl Blaha ◽  
Virginia Gonzalez ◽  
...  
Keyword(s):  
Heart Rate ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Pressor Response ◽  
Muscle Sympathetic Nerve Activity ◽  
Total Activity ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Pressor Responses ◽  
Averaging Techniques

Smoking is a risk factor for cardiovascular diseases. Prior reports showed a transient increase in blood pressure (BP) following a spontaneous burst of muscle sympathetic nerve activity (MSNA). We hypothesized that this pressor response would be accentuated in smokers. Using signal-averaging techniques, we examined the BP (Finometer) response to MSNA in 18 otherwise healthy smokers and 42 healthy nonsmokers during resting conditions. The sensitivities of baroreflex control of MSNA and heart rate were also assessed. The mean resting MSNA, heart rate, and mean arterial pressure (MAP) were higher in smokers than nonsmokers. The MAP increase following a burst of MSNA was significantly greater in smokers than nonsmokers (Δ3.4 ± 0.3 vs. Δ1.6 ± 0.1 mmHg, P < 0.001). The baroreflex sensitivity (BRS) of burst incidence, burst area, or total activity was not different between the two groups. However, cardiac BRS was lower in smokers than nonsmokers (14.6 ± 1.7 vs. 24.6 ± 1.5 ms/mmHg, P < 0.001). Moreover, the MAP increase following a burst was negatively correlated with the cardiac BRS. These observations suggest that habitual smoking in otherwise healthy individuals raises the MAP increase following spontaneous MSNA and that the attenuated cardiac BRS in the smokers was a contributing factor. We speculate that the accentuated pressor increase in response to spontaneous MSNA may contribute to the elevated resting BP in the smokers.

scholarly journals Whole body heat stress attenuates baroreflex control of muscle sympathetic nerve activity during postexercise muscle ischemia

2009 ◽  
Vol 106 (4) ◽  
pp. 1125-1131 ◽  
Author(s):  
Jian Cui ◽  
Manabu Shibasaki ◽  
Scott L. Davis ◽  
David A. Low ◽  
David M. Keller ◽  
...  
Keyword(s):  
Heart Rate ◽  
Heat Stress ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Whole Body ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Whole Body Heat Stress ◽  
Body Heat

Both whole body heat stress and stimulation of muscle metabolic receptors activate muscle sympathetic nerve activity (MSNA) through nonbaroreflex pathways. In addition to stimulating muscle metaboreceptors, exercise has the potential to increase internal temperature. Although we and others report that passive whole body heating does not alter the gain of the arterial baroreflex, it is unknown whether increased body temperature, often accompanying exercise, affects baroreflex function when muscle metaboreceptors are stimulated. This project tested the hypothesis that whole body heating alters the gain of baroreflex control of muscle sympathetic nerve activity (MSNA) and heart rate during muscle metaboreceptor stimulation engaged via postexercise muscle ischemia (PEMI). MSNA, blood pressure (BP, Finometer), and heart rate were recorded from 11 healthy volunteers. The volunteers performed isometric handgrip exercise until fatigue, followed by 2.5 min of PEMI. During PEMI, BP was acutely reduced and then raised pharmacologically using the modified Oxford technique. This protocol was repeated two to three times when volunteers were normothermic, and again during heat stress (increase core temperature ∼ 0.7°C) conditions. The slope of the relationship between MSNA and BP during PEMI was less negative (i.e., decreased baroreflex gain) during whole body heating when compared with the normothermic condition (−4.34 ± 0.40 to −3.57 ± 0.31 units·beat−1·mmHg−1, respectively; P = 0.015). The gain of baroreflex control of heart rate during PEMI was also decreased during whole body heating ( P < 0.001). These findings indicate that whole body heat stress reduces baroreflex control of MSNA and heart rate during muscle metaboreceptor stimulation.

scholarly journals Arterial Baroreflex Control of Multi‐ and Single‐Unit Muscle Sympathetic Nerve Activity in Young Unmedicated Hypertensives

2019 ◽  
Vol 33 (S1) ◽  
Author(s):  
Anthony V Incognito ◽  
Milena Samora ◽  
Andrew D Shepherd ◽  
Roberta A Cartafina ◽  
Gabriel MN Guimarães ◽  
...  
Keyword(s):  
Sympathetic Nerve ◽  
Single Unit ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control
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