Fig. 6. The core temperature plateau. The third phase of the hypothermia curve coincides with reemergence of thermoregulatory vasoconstriction. Vasoconstriction decreased cutaneous heat loss (adjusted for evaporative and respiratory loss) approximately 25 kcal/h. However, heat loss always exceeded heat production. Consequently, mean body temperature, which decreased at a rate of approximately 0.6°C/h before vasoconstriction, subsequently decreased at a rate of approximately 0.2°C/h. Core temperature also decreased at a rate of approximately 0.6°C before vasoconstriction, but remained virtually constant during the subsequent 2 h. Because mean body temperature and body heat content continued to decrease, constraint of metabolic heat to the core thermal compartment contributed to the core temperature plateau; that is, vasoconstriction reestablished the normal core-to-peripheral temperature gradient by preventing metabolic heat (which is largely generated in the core) from escaping to peripheral tissues. Constrained heat is presented cumulatively, referenced to vasoconstriction at elapsed time zero. Data are presented as the mean ± SD. Reprinted with permission from Kurz et al. 80