DETERMINATION OF HEAT DEBT IN THE COLD - PARTITIONAL CALORIMETRY VS CONVENTIONAL METHODS

Measurements of core temperature (T(c)) at different sites produce on some occasions different cooling curves in cold-exposed humans, suggesting that the corresponding thermometric heat debts (HD) could be equally different when calculated by conventional methods [via the change in either T(c) or mean body temperature (T(b)BAR)]. The present study also compared these thermometric HD values with the calorimetric HD obtained by partitional calorimetry (S). Nine subjects who showed similar initial but different final T(c) [rectal (T(re)) and auditory canal temperatures (T(ac))] during nude cold exposure (2 h at 1-degrees-C at rest) were used. T(c)-derived HD corresponded to a heat gain of 12 +/- 21 kJ and an HD of 78 +/- 20 kJ with use of T(re) and T(ac), respectively, whereas the T(b)BAR-derived HD varied from 266 +/- 35 to less-than-or-equal-to 1,479 +/- 71 kJ with the use of various well-known T(b)BAR weighing coefficients. In contrast, S corresponded to 504 +/- 79 kJ, a level that could have been obtained only if the thermoneutral/cold T(b)BAR weighing coefficients had been 0.818/0.818 for T(re) and 0.865/0.865 for T(ac). The results demonstrate that calculation by conventional methods can markedly overestimate or underestimate HD. These differences could not be explained by the site chosen to represent T(c), inasmuch as about the same effect was observed with use of either T(re) or T(ac). It is concluded that the thermometric value of HD in the cold is not, at least under the present conditions, as accurate and reliable as S.