Effect Of Palm Cooling On Reducing Heat Strain In Resting Hyperthermic Subjects

Abstract

Exposure to a non-compensable heat stress environment results in hyperthermia and risk of heat illness. In many military situations cooling methods are limited. One proposed method of personal cooling involves heat extraction from the palm using a device called the Rapid Thermal Exchanger (RTX). The palm is proposed as an efficient site for heat loss because of the many arteriovenous anastomoses allowing rapid heat exchange. PURPOSE: The present study evaluates whether the RTX reduces heart rate (HR), core temperature (Tes), mean skin temperature (Tsk), mean body temperature (Tb) and thermal/discomfort sensations in hyperthermic subjects passively seated in a hot, dry, environment. METHODS: Ten male subjects (mean ± SD; ht, 178.6 ± 5.3 cm, wt 74.8 ± 12.4 kg, age 25 ± 5yr, VO2 pk 57.3 ± 10.1 ml/kg/min−1) wearing military fatigues and MOP gear walked on a treadmill (3.8 mph, 4% grade) in a hot environment (42.2 ± 0.5°C, RH 37 ± 1%) until Tes reached 38.8°C (time 33.3 ± 10.5min). They then sat for 50 minutes in a semi-recumbent position with either no cooling (NC) or palm cooling (RTX: 10°C, flow rate 2.5 L/min, without negative pressure). Heat extraction from the palm during RTX trials was measured by direct calorimetry. RESULTS:TableWith RTX, Tes, Tsk, and Tb were significantly lower than NC from 15-50 minutes and thermal sensation was significantly lower from 30-50 minutes. CONCLUSION: Palm cooling with RTX reduced thermal strain in passive, hyperthermic subjects. With an average heat extraction of 37.1 ± 11 W the cooling capacity of RTX is modest compared to other published methods. However, in some military conditions (e.g. soldiers seated in a hot armored vehicle) RTX may extend field duration and reduce heat strain. Supported by DARPA W911NF-06-1-0025.