Modulation of control of muscle sympathetic nerve activity during orthostatic stress in humans

2004 ◽  
Vol 287 (5) ◽  
pp. H2147-H2153 ◽  
Author(s):  
Masashi Ichinose ◽  
Mitsuru Saito ◽  
Takeshi Ogawa ◽  
Keiji Hayashi ◽  
Narihiko Kondo ◽  
...  
Keyword(s):  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Total Activity ◽  
Orthostatic Stress ◽  
Lower Body ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Burst Strength

We tested the hypothesis that orthostatic stress would modulate the arterial baroreflex (ABR)-mediated beat-by-beat control of muscle sympathetic nerve activity (MSNA) in humans. In 12 healthy subjects, ABR control of MSNA (burst incidence, burst strength, and total activity) was evaluated by analysis of the relation between beat-by-beat spontaneous variations in diastolic blood pressure (DAP) and MSNA during supine rest (CON) and at two levels of lower body negative pressure (LBNP: −15 and −35 mmHg). At −15 mmHg LBNP, the relation between burst incidence (bursts per 100 heartbeats) and DAP showed an upward shift from that observed during CON, but the further shift seen at −35 mmHg LBNP was only marginal. The relation between burst strength and DAP was shifted upward at −15 mmHg LBNP (vs. CON) and further shifted upward at −35 mmHg LBNP. At −15 mmHg LBNP, the relation between total activity and DAP was shifted upward from that obtained during CON and further shifted upward at −35 mmHg LBNP. These results suggest that ABR control of MSNA is modulated during orthostatic stress and that the modulation is different between a mild (nonhypotensive) and a moderate (hypotensive) level of orthostatic stress.

scholarly journals Muscle sympathetic nerve activity during intense lower body negative pressure to presyncope in humans

2009 ◽  
Vol 587 (20) ◽  
pp. 4987-4999 ◽  
Author(s):  
William H. Cooke ◽  
Caroline A. Rickards ◽  
Kathy L. Ryan ◽  
Tom A. Kuusela ◽  
Victor A. Convertino
Keyword(s):  
Negative Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Lower Body ◽  
Nerve Activity

Effect of baroreflex loading on the responsiveness of the vestibulosympathetic reflex in humans

2007 ◽  
Vol 103 (3) ◽  
pp. 1001-1006 ◽  
Author(s):  
Damian J. Dyckman ◽  
Kevin D. Monahan ◽  
Chester A. Ray
Keyword(s):  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Total Activity ◽  
Saline Control ◽  
Otolith Organs ◽  
Lower Body ◽  
Nerve Activity ◽  
Vestibulosympathetic Reflex ◽  
Phenylephrine Infusion

Activation of the vestibular otolith organs with head-down rotation (HDR) increases muscle sympathetic nerve activity (MSNA) in humans. Previously, we demonstrated this vestibulosympathetic reflex (VSR) elicits increases in MSNA during baroreflex unloading (i.e., lower body negative pressure) in humans. Whether such an effect persists during baroreflex loading is unknown. We tested the hypothesis that the ability of the VSR to increase MSNA is preserved during baroreflex unloading and inhibited during baroreflex loading. Ten subjects (26 ± 1 yr) performed three trials of HDR to activate the VSR. These trials were performed after a period of sustained saline (control), nitroprusside (baroreflex unloading: 0.8–1.0 μg·kg−1·min−1), and phenylephrine (baroreflex loading: 0.6–0.8 μg·kg−1·min−1) infusion. Nitroprusside infusion decreased (Δ7 ± 1 mmHg, where Δ is change; P < 0.001) and phenylephrine infusion increased mean arterial pressure (Δ8 ± 1 mmHg; P < 0.001) at rest. HDR performed during the control [Δ3 ± 2 bursts/min, Δ314 ± 154 arbitrary units (au) total activity, Δ41 ± 18% total activity; P < 0.05] and nitroprusside trials [Δ5 ± 2 bursts/min, Δ713 ± 241 au total activity, Δ49 ± 20% total activity; P < 0.05] increased MSNA similarly despite significantly elevated levels at rest (13 ± 2 to 26 ± 3 bursts/min) in the latter. In contrast, HDR performed during the phenylephrine trial failed to increase MSNA (Δ0 ± 1 bursts/min, Δ−15 ± 33 au total activity, Δ−8 ± 21% total activity). These results confirm previous findings that the ability of the VSR to increase MSNA is preserved during baroreflex unloading. In contrast, the ability of the VSR to increase MSNA is abolished during baroreflex loading. These results provide further support for the concept that the VSR may act primarily to defend against hypotension in humans.

scholarly journals Asynchronous action potential discharge in human muscle sympathetic nerve activity

2019 ◽  
Vol 317 (4) ◽  
pp. H754-H764 ◽  
Author(s):  
Stephen A. Klassen ◽  
M. Erin Moir ◽  
Jacqueline K. Limberg ◽  
Sarah E. Baker ◽  
Wayne T. Nicholson ◽  
...  
Keyword(s):  
Action Potential ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Human Muscle ◽  
Lower Body ◽  
Nerve Activity ◽  
The Impact ◽  
Asynchronous Discharge

What strategies are employed by the sympathetic system to communicate with the circulation? Muscle sympathetic nerve activity (MSNA) occurs in bursts of synchronous action potential (AP) discharge, yet whether between-burst asynchronous AP firing exists remains unknown. Using multiunit microneurography and a continuous wavelet transform to isolate APs, we studied AP synchronicity within human MSNA. Asynchronous APs were defined as those which occurred between bursts. Experiment 1 quantified AP synchronicity in eight individuals at baseline (BSL), −10 mmHg lower body negative pressure (LBNP), −40 mmHg LBNP, and end-expiratory apnea (APN). At BSL, 33 ± 12% of total AP activity was asynchronous. Asynchronous discharge was unchanged from BSL (67 ± 37 AP/min) to −10 mmHg LBNP (69 ± 33 AP/min), −40 mmHg LBNP (83 ± 68 AP/min), or APN (62 ± 39 AP/min). Across all conditions, asynchronous AP probability and frequency decreased with increasing AP size. Experiment 2 examined the impact of the ganglia on AP synchronicity by using nicotinic blockade (trimethaphan). The largest asynchronous APs were derecruited from BSL (11 ± 4 asynchronous AP clusters) to the last minute of the trimethaphan infusion with visible bursts (7 ± 2 asynchronous AP clusters). However, the 6 ± 2 smallest asynchronous AP clusters could not be blocked by trimethaphan and persisted to fire 100 ± 0% asynchronously without forming bursts. Nonnicotinic ganglionic mechanisms affect some, but not all, asynchronous activity. The fundamental behavior of human MSNA contains between-burst asynchronous AP discharge, which accounts for a considerable amount of BSL activity. NEW & NOTEWORTHY Historically, sympathetic nerve activity destined for the blood vessels supplying skeletal muscle (MSNA) has been characterized by spontaneous bursts formed by synchronous action potential (AP) discharge. However, this study found a considerable amount (~30% during baseline) of sympathetic AP discharge to fire asynchronously between bursts of human MSNA. Trimethaphan infusion revealed that nonnicotinic ganglionic mechanisms contribute to some, but not all, asynchronous discharge. Asynchronous sympathetic AP discharge represents a fundamental behavior of MSNA.

Sympathetic nervous and hemodynamic responses to lower body negative pressure in hyperbaria in men

2002 ◽  
Vol 282 (1) ◽  
pp. R38-R45 ◽  
Author(s):  
Katsuya Yamauchi ◽  
Yuka Tsutsui ◽  
Yutaka Endo ◽  
Sueko Sagawa ◽  
Fumio Yamazaki ◽  
...  
Keyword(s):  
Negative Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Lower Body ◽  
Nerve Activity ◽  
Hyperbaric Environment ◽  
Hyperbaric Exposure ◽  
Forearm Vascular Resistance

The present study was designed to test the hypothesis that sympathetic nerve activity is attenuated in a hyperbaric environment. Response of muscle sympathetic nerve activity (MSNA) to central circulatory hypovolemic stress, lower body negative pressure (LBNP), was measured in nine men at normal and at 3 atm pressures. The stress consisted of 4 min each of control and LBNP at −20 and −40 mmHg. In addition to MSNA, heart rate, stroke volume (SV), forearm blood flow (FBF), and volume of the lower leg were recorded. A reduction of baseline HR occurred with increased forearm vascular resistance at 3 atm abs. The baseline MSNA decreased during hyperbaria. MSNA increased progressively with increasing LBNP in both atmospheric pressures, and the change from the baseline (ΔMSNA) was similar in both conditions. Changes in SV, FBF, and volume of the lower legs in response to LBNP were not statistically different during exposure to 2 atm pressures. The present study suggests that hyperbaria attenuates sympathetic nerve activity; however, its responsiveness to hypovolemic stress was not affected by hyperbaric exposure.

scholarly journals Muscle sympathetic nerve activity during lower body negative pressure is accentuated in heat-stressed humans

2004 ◽  
Vol 96 (6) ◽  
pp. 2103-2108 ◽  
Author(s):  
Jian Cui ◽  
Thad E. Wilson ◽  
Craig G. Crandall
Keyword(s):  
Negative Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Sweat Rate ◽  
Muscle Sympathetic Nerve Activity ◽  
Whole Body ◽  
Lower Body ◽  
Nerve Activity ◽  
Arterial Blood

The purpose of this project was to test the hypothesis that increases in muscle sympathetic nerve activity (MSNA) during an orthostatic challenge is attenuated in heat-stressed individuals. To accomplish this objective, MSNA was measured during graded lower body negative pressure (LBNP) in nine subjects under normothermic and heat-stressed conditions. Progressive LBNP was applied at -3, -6, -9, -12, -15, -18, -21, and -40 mmHg for 2 min per stage. Whole body heating caused significant increases in sublingual temperature, skin blood flow, sweat rate, heart rate, and MSNA (all P < 0.05) but not in mean arterial blood pressure ( P > 0.05). Progressive LBNP induced significant increases in MSNA in both thermal conditions. However, during the heat stress trial, increases in MSNA at LBNP levels higher than -9 mmHg were greater compared with during the same LBNP levels in normothermia (all P < 0.05). These data suggest that the increase in MSNA to orthostatic stress is not attenuated but rather accentuated in heat-stressed humans.

Sympathetic nerve activity in arm and leg muscles during lower body negative pressure in humans

1989 ◽  
Vol 66 (6) ◽  
pp. 2778-2781 ◽  
Author(s):  
R. F. Rea ◽  
B. G. Wallin
Keyword(s):  
Negative Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Sympathetic Outflow ◽  
Lower Body ◽  
Nerve Activity ◽  
Leg Muscles ◽  
Cardiopulmonary Receptors

Nonhypotensive lower body negative pressure (LBNP) is reported to decrease forearm but not calf blood flow as measured by strain-gauge plethysmography. This suggests that unloading of cardiopulmonary receptors increases sympathetic outflow to arm but not to leg. To test this hypothesis we measured muscle sympathetic nerve activity (MSA) in the arm (radial nerve) and leg (peroneal nerve) simultaneously during LBNP. In eight healthy subjects, we measured heart rate, blood pressure, and radial and peroneal MSA during LBNP at 10 and 20 mmHg. There was no difference between radial and peroneal MSA at rest, and there were successive parallel increases of MSA in both nerves during LBNP at 10 and 20 mmHg. These data indicate that there are nearly identical increases of sympathetic outflow to the arm and leg during mild to moderate degrees of orthostatic stress.

Modulation of arterial baroreflex control of muscle sympathetic nerve activity by muscle metaboreflex in humans

2004 ◽  
Vol 286 (2) ◽  
pp. H701-H707 ◽  
Author(s):  
Masashi Ichinose ◽  
Mitsuru Saito ◽  
Hiroyuki Wada ◽  
Asami Kitano ◽  
Narihiko Kondo ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Linear Relationship ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Total Activity ◽  
Arterial Baroreflex ◽  
Nerve Activity ◽  
Baroreflex Control ◽  
Muscle Metaboreflex ◽  
Burst Strength

We aimed to investigate the interaction [with respect to the regulation of muscle sympathetic nerve activity (MSNA) and blood pressure] between the arterial baroreflex and muscle metaboreflex in humans. In 10 healthy subjects who performed a 1-min sustained handgrip exercise at 50% maximal voluntary contraction followed by forearm occlusion, arterial baroreflex control of MSNA (burst incidence and strength and total activity) was evaluated by analyzing the relationship between beat-by-beat spontaneous variations in diastolic arterial blood pressure (DAP) and MSNA both during supine rest (control) and during postexercise muscle ischemia (PEMI). During PEMI (vs. control), 1) the linear relationship between burst incidence and DAP was shifted rightward with no alteration in sensitivity, 2) the linear relationship between burst strength and DAP was shifted rightward and upward with no change in sensitivity, and 3) the linear relationship between total activity and DAP was shifted to a higher blood pressure and its sensitivity was increased. The modification of the control of total activity that occurs in PEMI could be a consequence of alterations in the baroreflex control of both MSNA burst incidence and burst strength. These results suggest that the arterial baroreflex and muscle metaboreflex interact to control both the occurrence and strength of MSNA bursts.

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