Cooling Capacity of Transpulmonary Cooling and Cold-Water Immersion After Exercise-Induced Hyperthermia

Abstract

Context Cold-water immersion (CWI) may not be feasible in some remote settings, prompting the identification of alternative cooling methods as adjunct treatment modalities for exertional heat stroke (EHS). Objective To determine the differences in cooling capacities between CWI and the inhalation of cooled air. Design Randomized controlled clinical trial. Setting Laboratory. Patients or Other Participants A total of 12 recreationally active participants (7 men, 5 women; age = 26 ± 4 years, height = 170.6 ± 10.1 cm, mass = 76.0 ± 18.0 kg, body fat = 18.5% ± 9.7%, peak oxygen uptake = 42.7 ± 8.9 mL·kg−1·min−1). Intervention(s) After exercise in a hot environment (40°C and 40% relative humidity), participants were randomized to 3 cooling conditions: cooling during passive rest (PASS; control), CWI, and the Polar Breeze thermal rehabilitation machine (PB) with which participants inspired cooled air (22.2°C ± 1.0°C). Main Outcome Measure(s) Rectal temperature (TREC) and heart rate were continuously measured throughout cooling until TREC reached 38.25°C. Results Cooling rates during CWI (0.18°C·min−1 ± 0.06°C·min−1) were greater than those during PASS (mean difference [95% CI] of 0.16°C·min−1 [0.13°C·min−1, 0.19°C·min−1]; P < .001) and PB (0.15°C·min−1 [0.12°C·min−1, 0.16°C·min−1]; P < .001). Elapsed time to reach a TREC of 38.25°C was also faster with CWI (9.71 ± 3.30 minutes) than PASS (−58.1 minutes [−77.1, −39.9 minutes]; P < .001) and PB (−46.8 minutes [−65.5, −28.2 minutes]; P < .001). Differences in cooling rates and time to reach a TREC of 38.25°C between PASS and PB were not different (P > .05). Conclusions Transpulmonary cooling via cooled-air inhalation did not promote an optimal cooling rate (>0.15°C·min−1) for the successful treatment of EHS. In remote settings where EHS is a risk, access and use of treatment methods via CWI or cold-water dousing are imperative to ensuring survival. Trial Registry ClinicalTrials.gov (NCT0419026).