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Record Details

Record 48 of 1688
Exercise thermoregulation in men after 1 and 24-hours of 6 degrees head-down tilt
Author and Affiliation:
Ertl, A. C.(NASA Ames Research Center, Moffett Field CA United States)
Dearborn, A. S.
Weidhofer, A. R.
Bernauer, E. M.
Greenleaf, J. E.
Abstract: BACKGROUND: Exercise thermoregulation is dependent on heat loss by increased skin blood flow (convective and conductive heat loss) and through enhanced sweating (evaporative heat loss). Reduction of plasma volume (PV), increased plasma osmolality, physical deconditioning, and duration of exposure to simulated and actual microgravity reduces the ability to thermoregulate during exercise. HYPOTHESIS: We hypothesized that 24 h of head down tilt (HDT24) would alter thermoregulatory responses to a submaximal exercise test and result in a higher exercise rectal temperature (Tre) when compared with exercise Tre after 1 h of head down tilt (HDT1). METHODS: Seven men (31+/-SD 6 yr, peak oxygen uptake (VpO2peak) of 44+/-6 ml x kg(-1) x min(-1)) were studied during 70 min of supine cycling at 58+/-SE 1.5% VO2peak at 22.0 degrees C Tdb and 47% rh. RESULTS: Relative to pre-tilt sitting chair rest data, HDT1 resulted in a 6.1+/-0.9% increase and HDT24 in a 4.3+/-2.3% decrease in PV (delta = 10.4% between experiments, p<0.05) while plasma osmolality remained unchanged (NS). Pre-exercise Tre was elevated after HDT24 (36.71 degrees C +/-0.06 HDT1 vs. 36.93 degrees C+/-0.11 HDT24, p<0.05). The 70 min of exercise did not alter this relationship (p<0.05) with respective end exercise increases in Tre to 38.01 degrees C and 38.26 degrees C (degrees = 1.30 degrees C (HDT1) and 1.33 degrees C (HDT24)). While there were no pre-exercise differences in mean skin temperature (Tsk), a significant (p<0.05) time x treatment interaction occurred during exercise: after min 30 in HDT24 the Tsk leveled off at 31.1 degrees C, while it continued to increase reaching 31.5 degrees C at min 70 in HDT1. A similar response (NS) occurred in skin blood velocity. Neither local sweating rates nor changes in body weight during exercise of -1.63+/-0.24 kg (HDT1) or - 1.33+/-0.09 kg (HDT24) were different (NS) between experiments. CONCLUSION: While HDT24 resulted in elevated pre-exercise Tre, reduced PV, attenuation of Tsk and skin blood velocity during exercise, the absolute increase in exercise Tre was not altered. But if sweat rate and cutaneous vascular responses were similar at different core temperatures (unchanged thermoregulation), the Tre offset could have been caused by the HDT-induced hypovolemia.
Publication Date: Feb 01, 2000
Document ID:
20040141659
(Acquired Nov 09, 2004)
Subject Category: AEROSPACE MEDICINE
Document Type: Journal Article
Publication Information: Aviation, space, and environmental medicine (ISSN 0095-6562); Volume 71; 2; 150-5
Publisher Information: United States
Description: In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: AEROSPACE MEDICINE; GRAVITATIONAL PHYSIOLOGY; HEAD DOWN TILT; HUMAN BEINGS; HYPOKINESIA; MALES; PHYSICAL EXERCISE; PHYSIOLOGICAL RESPONSES; THERMOREGULATION; WEIGHTLESSNESS SIMULATION; ADULTS; BLOOD FLOW; BLOOD PLASMA; BLOOD VOLUME; BODY TEMPERATURE; FLOW VELOCITY; OSMOSIS; OXYGEN CONSUMPTION; PERSPIRATION; PHYSIOLOGICAL TESTS; SKIN (ANATOMY); SKIN TEMPERATURE (BIOLOGY); TIME DEPENDENCE
Other Descriptors: BODY TEMPERATURE REGULATION/PHYSIOLOGY; EXERCISE/PHYSIOLOGY; HEAD-DOWN TILT/ADVERSE EFFECTS; SPACE FLIGHT; WEIGHTLESSNESS SIMULATION/ADVERSE EFFECTS; ADULT; BLOOD FLOW VELOCITY; BODY TEMPERATURE; COMPARATIVE STUDY; EXERCISE TEST; HUMAN; MALE; OSMOLAR CONCENTRATION; OXYGEN CONSUMPTION; PLASMA VOLUME; SKIN/BLOOD SUPPLY; SKIN TEMPERATURE; SUPPORT, U.S. GOV'T, NON-P.H.S; SWEATING/PHYSIOLOGY; TIME FACTORS; NASA CENTER ARC; NASA DISCIPLINE REGULATORY PHYSIOLOGY; NASA PROGRAM BIOMEDICAL RESEARCH AND COUNTERMEASURES
Availability Source: Other Sources
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