Reply to the discussion by B. Harris on “Core cooling and thermal responses during whole-head, facial, and dorsal immersion in 17 °C water”

Abstract

The authors appreciate the interest in our recent paper on core cooling and thermal responses during whole-head, facial, and dorsal immersion in 17 °C water (Pretorius et al. 2010). We demonstrated that, although whole-head cooling elicited a higher rate of fingertip vasoconstriction, the face did not elicit more vasoconstriction than the dorsum. Rather, the progressive increase in core cooling from dorsal to face to whole-head immersion simply correlated with increased heat loss from the head. First, the rate of core cooling, relative to head heat loss, was similar between the 3 conditions, and the values for the first 30 min (0.0039 °C·kJ–1) were similar to the total 60-min period (0.0036 °C·kJ–1); thus lower heat loss in the second 30 min paralleled slower core cooling. Second, blood flow changes in acral areas (i.e., the fingertips) do not necessarily correlate with changes in non-acral areas (i.e., scalp and (or) facial skin). In our study, scalp/facial blood flow was not measured directly but could be inferred by heat loss, which decreased similarly from the first to second 30-min periods in each condition. Finally, the amount of increased respiratory heat loss in the face-immersion condition was likely small in amount, and minimal in effect. We did not measure inspired air temperature but even if the inspirate cooled completely to the surrounding water temperature (17 °C) as it passed through the submersed portion of the snorkel, the maximal drop in air temperature would be only ∼5 °C. This small amount of air cooling at low resting ventilation levels would not significantly affect airway or core cooling (Johnston et al. 1996).