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.

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

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.

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.

scholarly journals Attenuated sympathetic nerve responses after 24 hours of bed rest

2002 ◽  
Vol 282 (6) ◽  
pp. H2210-H2215 ◽  
Author(s):  
Mazhar H. Khan ◽  
Allen R. Kunselman ◽  
Urs A. Leuenberger ◽  
William R. Davidson ◽  
Chester A. Ray ◽  
...  
Keyword(s):  
Cardiac Output ◽  
Negative Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Bed Rest ◽  
Nerve Activity ◽  
Before And After ◽  
Reduced Rate

Bed rest reduces orthostatic tolerance. Despite decades of study, the cause of this phenomenon remains unclear. In this report we examined hemodynamic and sympathetic nerve responses to graded lower body negative pressure (LBNP) before and after 24 h of bed rest. LBNP allows for baroreceptor disengagement in a graded fashion. We measured heart rate (HR), cardiac output (HR × stroke volume obtained by echo Doppler), and muscle sympathetic nerve activity (MSNA) during a progressive and graded LBNP paradigm. Negative pressure was increased by 10 mmHg every 3 min until presyncope or completion of −60 mmHg. After bed rest, LBNP tolerance was reduced in 11 of 13 subjects ( P < .023), HR was greater ( P< .002), cardiac output was unchanged, and the ability to augment MSNA at high levels of LBNP was reduced (rate of rise for 30- to 60-mmHg LBNP before bed rest 0.073 bursts · min−1 · mmHg−1; after bed rest 0.035 bursts · min−1 · mmHg−1; P < 0.016). These findings suggest that 24 h of bed rest reduces sympathetic nerve responses to LBNP.

Cardiopulmonary baroreceptor control of muscle sympathetic nerve activity in heat-stressed humans

1999 ◽  
Vol 277 (6) ◽  
pp. H2348-H2352 ◽  
Author(s):  
C. G. Crandall ◽  
R. A. Etzel ◽  
D. B. Farr
Keyword(s):  
Blood Pressure ◽  
Heat Stress ◽  
Arterial Blood Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Muscle Sympathetic Nerve Activity ◽  
Venous Pressure ◽  
Whole Body ◽  
Nerve Activity ◽  
Arterial Blood

Whole body heating decreases central venous pressure (CVP) while increasing muscle sympathetic nerve activity (MSNA). In normothermia, similar decreases in CVP elevate MSNA, presumably via cardiopulmonary baroreceptor unloading. The purpose of this project was to identify whether increases in MSNA during whole body heating could be attributed to cardiopulmonary baroreceptor unloading coincident with the thermal challenge. Seven subjects were exposed to whole body heating while sublingual temperature, skin blood flow, heart rate, arterial blood pressure, and MSNA were monitored. During the heat stress, 15 ml/kg warmed saline was infused intravenously over 7–10 min to increase CVP and load the cardiopulmonary baroreceptors. We reported previously that this amount of saline was sufficient to return CVP to pre-heat stress levels. Whole body heating increased MSNA from 25 ± 3 to 39 ± 3 bursts/min ( P < 0.05). Central blood volume expansion via rapid saline infusion did not significantly decrease MSNA (44 ± 4 bursts/min, P > 0.05 relative to heat stress period) and did not alter mean arterial blood pressure (MAP) or pulse pressure. To identify whether arterial baroreceptor loading decreases MSNA during heat stress, in a separate protocol MAP was elevated via steady-state infusion of phenylephrine during whole body heating. Increasing MAP from 82 ± 3 to 93 ± 4 mmHg ( P < 0.05) caused MSNA to decrease from 36 ± 3 to 15 ± 4 bursts/min ( P < 0.05). These data suggest that cardiopulmonary baroreceptor unloading during passive heating is not the primary mechanism resulting in elevations in MSNA. Moreover, arterial baroreceptors remain capable of modulating MSNA during heat stress.

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.

Comparison of muscle sympathetic responses to hemorrhage and lower body negative pressure in humans

1991 ◽  
Vol 70 (3) ◽  
pp. 1401-1405 ◽  
Author(s):  
R. F. Rea ◽  
M. Hamdan ◽  
M. P. Clary ◽  
M. J. Randels ◽  
P. J. Dayton ◽  
...  
Keyword(s):  
Negative Pressure ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Venous Pressure ◽  
Lower Body ◽  
Central Venous ◽  
Nerve Activity ◽  
Percent Change ◽  
Sympathetic Responses

We compared changes in muscle sympathetic nerve activity (SNA) during graded lower body negative pressure (LBNP) and 450 ml of hemorrhage in nine healthy volunteers. During LBNP, central venous pressure (CVP) decreased from 6.1 +/- 0.4 to 4.5 +/- 0.5 (LBNP -5 mmHg), 3.4 +/- 0.6 (LBNP -10 mmHg), and 2.3 +/- 0.6 mmHg (LBNP -15 mmHg), and there were progressive increases in SNA at each level of LBNP. The slope relating percent change in SNA to change in CVP during LBNP (mean +/- SE) was 27 +/- 11%/mmHg. Hemorrhage of 450 ml at a mean rate of 71 +/- 5 ml/min decreased CVP from 6.1 +/- 0.5 to 3.7 +/- 0.5 mmHg and increased SNA by 47 +/- 11%. The increase in SNA during hemorrhage was not significantly different from the increase in SNA predicted by the slope relating percent change in SNA to change in CVP during LBNP. These data show that nonhypotensive hemorrhage causes sympathoexcitation and that sympathetic responses to LBNP and nonhypotensive hemorrhage are similar in humans.

Low-Dose Fentanyl Does Not Alter Muscle Sympathetic Nerve Activity, Blood Pressure, or Tolerance During Progressive Central Hypovolemia

2021 ◽  
Author(s):  
Mu Huang ◽  
Joseph C. Watso ◽  
Luke Belval ◽  
Frank A. Cimino III ◽  
Mads Fischer ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Sympathetic Nerve ◽  
Sympathetic Nerve Activity ◽  
Lower Body Negative Pressure ◽  
Muscle Sympathetic Nerve Activity ◽  
Controlled Trial ◽  
Stress Index ◽  
Nerve Activity ◽  
Arterial Blood ◽  
Analgesic Dose

Hemorrhage is a leading cause of battlefield and civilian trauma deaths. Several pain medications, including fentanyl, are recommended for use in the prehospital (i.e., field setting) for a hemorrhaging solider. However, it is unknown whether fentanyl impairs arterial blood pressure (BP) regulation, which would compromise hemorrhagic tolerance. Thus, the purpose of this study was to test the hypothesis that an analgesic dose of fentanyl impairs hemorrhagic tolerance in conscious humans. Twenty-eight volunteers (13 females) participated in this double-blinded, randomized, placebo-controlled trial. We conducted a pre-syncopal limited progressive lower-body negative pressure test (LBNP; a validated model to simulate hemorrhage) following intravenous administration of fentanyl (75 µg) or placebo (saline). We quantified tolerance as a cumulative stress index (mmHg•min), which was compared between trials using a paired, two-tailed t-test. We also compared muscle sympathetic nerve activity (MSNA; microneurography) and beat-to-beat BP (photoplethysmography) during the LBNP test using a mixed effects model (time [LBNP stage] x trial). LBNP tolerance was not different between trials (Fentanyl: 647 ± 386 vs. Placebo: 676 ± 295 mmHg•min, P=0.61, Cohen's d = 0.08). Increases in MSNA burst frequency (time: p<0.01, trial: p=0.29, interaction: p=0.94) and reductions in mean BP (time: p<0.01, trial: p=0.50, interaction: p=0.16) during LBNP were not different between trials. These data, the first to be obtained in conscious humans, demonstrate that administration of an analgesic dose of fentanyl does not alter MSNA or BP during profound central hypovolemia, nor does it impair tolerance to this simulated hemorrhagic insult.

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