Evaluating physiological strain during cold exposure using a new cold strain index

A cold strain index (CSI) based on core (T-core) and mean skin temperatures ((T) over bar(sk)) and capable of indicating cold strain in real time and analyzing existing databases has been developed. This index rates cold stra in on a universal scale of 0-10 and is as follows: CSI = 6.67(T-coret - T-c ore0) . (35 - T-core0)(-1) + 3.33((T) over bar(skt) - (T) over bar(sk0)) . (20 - (T) over bar(sk0))(-1), where T-core0 and (T) over bar(sk0) are initi al measurements and T-coret and (T) over bar(skt) are simultaneous measurem ents taken at any time t; when T-coret > T-core0, then T-coret - T-core0 = 0. CSI was applied to three databases. The first database was obtained from nine men exposed to cold air (7 degrees C, 40% relative humidity) for 120 min during euhydration and two hypohydration conditions achieved by exercis e-heat stress-induced sweating or by ingestion of furosemide 12 h before co ld exposure. The second database was from eight men exposed to cold air (10 degrees C) immediately on completion of 61 days of strenuous outdoor milit ary training, 48 h later, and after 109 days. The third database was from e ight men repeatedly immersed in 20 degrees C water three times in 1 day and during control immersions. CSI significantly differentiated (P < 0.01) bet ween the trials and individually categorized the strain of the subject for two of these three databases. This index has the potential to be widely acc epted and used universally.