[Body temperature changes during 7 d -6 degrees head-down bed rest].
Objective. To investigate body temperature changes in man during 7-day -6 degrees head-down bed rest (BR). Method. Body temperatures were measured in the morning (6:00), afternoon (16:00) and evening (20:00) during 7 d BR in 18 healthy males (18-22 years old). Result. Rectal temperature (Tre) in the morning gradually decreased as time (d) of BR increased: after the 4th day of BR (BR4d), Tre significantly reduced compared with the supine control (SC, 36.50 +/- 0.03 degrees C) before BR, and it consistently declined to 36.38 +/- 0.04 degrees C on BR7d; But Tre significantly increased in the afternoon after BR5d and in the evening after BR1d, with the final increments of 0.12 +/- 0.05 degrees C and 0.25 +/- 0.03 degrees C respectively on BR7d. Mean body temperature (Tsk) in the morning was significantly higher from BR2d than its SC, with a final net increase (delta Tsk) of 0.38 +/- 0.14 degrees C on BR7d. And Tsk significantly increased in the afternoon and evening from BR4d, BR2d respectively. Skin temperature on the forehead (Tforehead) elevated in the morning during BR. While in the afternoon and evening, Tforehead were significantly higher from BR7d and BR6d than their SC. Conclusion. Both the difference in time of recording at a BR day and the time (d) of BR have significant influence on Tre, Tsk , and Tforehead (P<0.01). These data suggest that body temperature rhythm, body fluid loss and headward distribution, hypokinesis etc. induced by BR have an impact on human thermal regulation during BR.