Sleep restriction does not affect orthostatic tolerance in the simulated microgravity environment

• Published in: Journal of applied physiology (1985) Vol. 97; no. 5; pp. 1660 - 1666
• Main Authors: Grenon, S. Marlene, Hurwitz, Shelley, Sheynberg, Natalie, Xiao, Xinshu, Judson, Brad, Ramsdell, Craig D, Kim, Christine, Cohen, Richard J, Williams, Gordon H
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.11.2004; American Physiological Society
• Subjects: Adult; Applied physiology; Bed Rest; Biological and medical sciences; Cardiovascular system; Cardiovascular System - physiopathology; Endocrine Glands - physiopathology; Excretion; Gravity; Head-Down Tilt; Human physiology applied to population studies and life conditions. Human ecophysiology; Humans; Hypotension, Orthostatic - physiopathology; Hypotension, Orthostatic - urine; Kidney - physiopathology; Male; Medical sciences; Potassium - urine; Renin - urine; Simulation; Sleep; Sleep Deprivation; Sleep disorders; Sodium - urine; Transports. Aerospace. Diving. Altitude; Weightlessness Simulation; Human; Crew; Deprivation; Astronaut; Mineralocorticoid; Environmental factor; Weightlessness; Space flight; Aldosterone; renin-angiotensin-aldosterone system; Renin angiotensin system; Sleep; Simulation; autonomic function; Orthostatic tolerance; Microgravity; NASA Discipline Cardiopulmonary; Non-NASA Center
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00328.2004

1 Division of Endocrinology, Hypertension and Diabetes, Brigham and Women's Hospital, Boston 02115; and 2 NASA Center for Quantitative Cardiovascular Physiology, Modeling and Data Analysis, Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; and 3 Department of Cardio-Thoracic Surgery, McGill University, Montreal, Quebec, Canada H3G 1A4 Submitted 25 March 2004 ; accepted in final form 23 June 2004 Orthostatic intolerance (OI) is a major problem following spaceflight, and, during flight, astronauts also experience sleep restriction. We hypothesized that sleep restriction will compound the risk and severity of OI following simulated microgravity and exaggerate the renal, cardioendocrine, and cardiovascular adaptive responses to it. Nineteen healthy men were equilibrated on a constant diet, after which they underwent a tilt-stand test. They then completed 14–16 days of simulated microgravity [head-down tilt bed rest (HDTB)], followed by repeat tilt-stand test. During HDTB, 11 subjects were assigned to an 8-h sleep protocol (non-sleep restricted), and 8 were assigned to a sleep-restricted protocol with 6 h of sleep per night. During various phases, the following were performed: 24-h urine collections, hormonal measurements, and cardiovascular system identification. Development of presyncope or syncope defined OI. There was a significant decrease in time free of OI ( P = 0.02) and an increase in OI occurrence ( P = 0.06) after HDTB among all subjects. However, the increase in OI occurrence did not differ significantly between the two groups ( P = 0.60). The two groups also experienced similar physiological changes with HDTB (initial increase in sodium excretion; increased excretion of potassium at the end of HDTB; increase in plasma renin activity secretion without a change in serum or urine aldosterone). No significant change in autonomic function or catecholamines was noted. Simulated microgravity leads to increased OI, and sleep restriction does not additively worsen OI in simulated microgravity. Furthermore, conditions of sleep restriction and nonsleep restriction are similar with respect to renal, cardioendocrine, and cardiovascular responses to simulated microgravity. renin-angiotensin-aldosterone system; autonomic function Address for reprint requests and other correspondence: G. H. Williams, Division of Endocrinology, Hypertension and Diabetes, BWH, 221 Longwood Ave., Boston, MA 02115 (E-mail: gwilliams{at}partners.org ).