Effects of ambient temperature on nitrogen uptake and elimination in humans

Tissue nitrogen (N2) exchange is primarily dependent on circulation, which may be modified by body thermal status. Thermal effects on uptake and washout of N2 have not been systematically investigated earlier. In the present study of eight subjects, N2 was washed out in thermally neutral ambient conditions (TN; skin temperature (Ts) = 33.69 ± 0.84 degrees C), then washed in during either TN, cool (Ts 30.25 ± 4.15 degrees C) or warm (Ts = 35.81 ± 0.82 degrees C) conditions. It was then washed out during various combinations of those conditions. N2 exchange was monitored during 125 minutes of breathing a normoxic oxygen/argon mixture (Phase I) followed by room air for 125 minutes of N2 reloading (Phase II; no N2 recording) and then 125 minutes N2 washout (Phase III) in order to determine the amount of N2 taken up during Phase II. Cool conditions reduced cardiac output, while warm conditions increased it compared to TN. Among the five Phase I TN recordings in the eight subjects (i.e., 40 control experiments) the N2 yield averaged 857.2 ± 15.3 mL. The reloaded N2 volume in Phase II was significantly smaller during the cool condition (8%, p ≤ 0.05) and significantly larger (22%, p ≤ 0.05) during the warm. The N2 washed out in 125 minutes was significantly less during cold (6%, p ≤ 0.05) and greater during warm conditions (18%, p ≤ 0.05). These observations are consistent with previously reported circulatory changes in cool and warm conditions and effects of thermal status on venous gas bubble dynamics and incidents of decompression sickness.