Relative role of low- and high pressure reflexes on sympathetic activity in humans during simulated gravitational stress

• Published in: Journal of gravitational physiology Vol. 3; no. 1; p. 29
• Main Authors: Gabrielsen, A, Petersen, H H, Johansen, L B, Foldager, N, Christensen, N J, Norsk, P
• Format: Journal Article
• Language: English
• Published: United States 01.04.1996
• Subjects: Adult; Baroreflex - physiology; Blood Pressure - physiology; Cardiovascular Physiological Phenomena; Carotid Sinus - physiology; Central Venous Pressure - physiology; Epinephrine - blood; Epinephrine - metabolism; Heart Rate - physiology; Hemodynamics - physiology; Humans; Lower Body Negative Pressure; Male; Norepinephrine - blood; Norepinephrine - metabolism; Pressoreceptors - physiology; Pulse - physiology; Stroke Volume - physiology; Sympathetic Nervous System - physiology
• ISSN: 1077-9248

In order to determine the relative role of low- and high-pressure reflexes, respectively, on forearm sympathetic nerve activity (fSNA), 10 normal male subjects underwent a 4-step (5 min each) graded lower body negative pressure (LBNP) from -10 to -50 mmHg. Central venous pressure (CVP) and stroke volume gradually decreased (p<0.05), and arterial pulse pressure (PP) abruptly decreased at LBNP of -50 mmHg. Mean arterial pressure (MAP) remained unchanged. Forearm venous plasma norepinephrine concentration (fvNE) increased significantly at LBNP of -35 mmHg (p<0.05) and with a further sharp increase during LBNP of -50 mmHg (p<0.05). High degrees of intra-individual correlations were observed between changes in Log [fvNE] and CVP (r-values from -0.78 to -0.96, p<0.01). We conclude that low-pressure reflexes are the major determinants of fSNA during non-hypotensive gravitational stress (MAP and PP unchanged). When the gravitational stress is more pronounced, a decrease in PP further augments fSNA through inhibition of high-pressure arterial baroreflexes.