BODY-TEMPERATURE AND THERMOREGULATION DURING SUBMAXIMAL EXERCISE AFTER 115-DAY SPACEFLIGHT

Background: Altered thermoregulation has been reported following space flight simulations (bed rest and water immersion) but has never been e xamined after actual spaceflight. Hypothesis: We tested the null hypot hesis that body temperatures and heat loss responses during exercise w ould be similar before and after spaceflight. Methods: Two male crewme mbers of the 115-d Mir 18 mission performed supine submaximal cycle ex ercise (20 min at 40% and 20 min at 65% of preflight (V) over dot O(2) peak) once at 145-146 d preflight and once at 5 d postflight (R + 5). Results: After flight neither crewmember could complete the exercise p rotocol, stopping after 28-29 min. The core temperature (Tin, ingestib le telemetry pill) at test termination was similar (37.8 degrees C for both subjects) pre-and postflight despite shorter postflight test dur ation. The slopes or the skin blood flow (laser Doppler)/Tin relations hip (subject 1: 396 vs. 214; subject 2: 704 vs. 143% change Perfusion Unit/degrees C), and the sweating rate (dew point hygrometry)/Tin rela tionship (subject 1: 6.3 vs. 2.0; subject 2: 4.6 vs. 0.7 mg.min(-1).cm (-2).degrees C-1), were both reduced postflight without appreciable ch ange in the Tin thresholds for sweating or skin blood flow. Conclusion : in this preliminary report for two crew members, the sensitivity of the heat loss responses were reduced after long-duration spaceflight, resulting ina faster rate of rise in core temperature.