title: Sympathetic nervous and hemodynamic responses to lower body negative pressure in hyperbaria in men.
abstract: 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 (DeltaMSNA) 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.
authors.affiliation: Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Yamauchi
authors.forename: Yuka
authors.initials: Y
authors.lastname: Tsutsui
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Endo
authors.forename: Sueko
authors.initials: S
authors.lastname: Sagawa
authors.forename: Fumio
authors.initials: F
authors.lastname: Yamazaki
authors.forename: Keizo
authors.initials: K
authors.lastname: Shiraki
mesh_terms: D000328:Adult; D001274:Atmospheric Pressure; D001794:Blood Pressure / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D020896:Hypovolemia / Q000503:physiopathology; D008150:Lower Body Negative Pressure; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009638:Norepinephrine / Q000097:blood; D011311:Pressoreceptors / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology; D013312:Stress, Physiological / Q000503:physiopathology; D013318:Stroke Volume / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*
chemical_list: D009638:Norepinephrine