Human muscle sympathetic neural and haemodynamic responses to tilt following spaceflight

• DOI: 10.1113/jphysiol.2001.012575
• Publication Date: 2002-07-27T12:45:57Z
• Authors: Benjamin D. Levine; James A. Pawelczyk; Andrew C. Ertl; James F. Cox; Julie H. Zuckerman; André Diedrich; Italo Biaggioni; Chester A. Ray; Michael L. Smith; Satoshi Iwase; Mitsuru Saito; Yoshiki Sugiyama; Tadaaki Mano; Rong Zhang; Kenichi Iwasaki; Lynda D. Lane; Jay C. Buckey; William H. Cooke; Friedhelm J. Baisch; David Robertson; Dwain L. Eckberg; C. Gunnar Blomqvist
• Keywords: Spaceflight; Supine position; Orthostatic intolerance; Weightlessness; Sympathetic nervous system

Orthostatic intolerance is common when astronauts return to Earth: after brief spaceflight, up two‐thirds are unable remain standing for 10 min. Previous research suggests that susceptible individuals increase their systemic vascular resistance and plasma noradrenaline concentrations above pre‐flight upright levels. In this study, we tested the hypothesis adaptation microgravity of space impairs sympathetic neural responses posture on Earth. We studied six ∼72 23 days before landing day 16 Neurolab shuttle mission. measured heart rate, arterial pressure cardiac output, calculated stroke volume total peripheral resistance, during supine rest min 60 deg tilt. Muscle nerve activity was recorded in five subjects, as a direct measure nervous system responses. As previous studies, mean (± s.e.m .) lower (46 ± 5 vs . 76 3 ml, P = 0.017) rate higher (93 1 74 4 beats −1 , 0.002) tilt spaceflight than spaceflight. Total post flight some, but not all (1674 256 1372 62 dynes s cm −5 0.32). No crew member exhibited orthostatic hypotension or presyncopal symptoms postflight tilting. (27 17 2 bursts 0.04) tilted 38 0.01) positions. A strong ( r 0.91–1.00) linear correlation between left ventricular muscle suggested were appropriate haemodynamic challenge unaffected by conclude normal.