A vascular mechanism to explain thermally mediated variations in deep‐body cooling rates during the immersion of profoundly hyperthermic individuals

Abstract

Physiologically trivial time differences for cooling the intrathoracic viscera of hyperthermic individuals have been reported between cold- and temperate-water immersion treatments. One explanation for that observation is reduced convective heat delivery to the skin during cold immersion, and this study was designed to test both the validity of that observation, and its underlying hypothesis. Eight healthy men participated in four head-out water immersions: two when normothermic, and two after exercise-induced, moderate-to-profound hyperthermia. Two water temperatures were used within each thermal state: temperate (26°C) and cold (14°C). Tissue temperatures were measured at three deep-body sites (oesophagus, auditory canal and rectum) and eight skin surfaces, with cutaneous vascular responses simultaneously evaluated from both forearms (laser-Doppler flowmetry and venous-occlusion plethysmography). During the cold immersion of normothermic individuals, oesophageal temperature decreased relative to baseline (-0.31°C over 20 min; P < 0.05), whilst rectal temperature increased (0.20°C; P < 0.05). When rendered hyperthermic, oesophageal (-0.75°C) and rectal temperatures decreased (-0.05°C) during the transition period (<8.5 min, mostly in air at 22°C), with the former dropping to 37.5°C only 54 s faster when immersed in cold rather than in temperate water (P < 0.05). Minimal cutaneous vasoconstriction occurred during either normothermic immersion, whereas pronounced constriction was evident during both immersions when subjects were hyperthermic, with the colder water eliciting a greater vascular response (P < 0.05). It was concluded that the rapid intrathoracic cooling of asymptomatic, hyperthermic individuals in temperate water was a reproducible phenomenon, with slower than expected cooling in cold water brought about by stronger cutaneous vasoconstriction that reduced convective heat delivery to the periphery.

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies

“…Indeed, a recent study found similar cooling rates using 14°C and 26°C water due to an attenuated vasoconstrictor drive at 26°C (161). Nevertheless, the mixture of warm 'central blood' with cool 'peripheral blood', will reduce core body temperature after termination of immersion in very cold water (i.e.…”

2020 International Consensus on First Aid Science With Treatment Recommendations

“…Cold-water immersion of the torso compared with temperate-water immersion of the torso (20 CÀ 26 C/68 FÀ 78.8 F) 21,22,26 Cold-water immersion (14 C/57.2 F) of the torso compared with the use of colder-water immersion (8 C/46.4 F) 26 Cold-water immersion (14 C/57.2 F) of the torso compared with ice-water immersion (2 CÀ 5 C/35.6 FÀ 41 F) of the torso 14,26 Colder-water immersion (9 C/48.2 F) up to the iliac crest compared with passive cooling 50 Colder-water immersion (10 CÀ 12 C/50.0 FÀ 52.6 F) of the hands/feet compared with the use of colder-water immersion of the torso 29 Evaporative cooling compared with passive cooling 34,52 Evaporative cooling compared with use of ice packs applied to the neck, axilla, and groin 34,36 Evaporative cooling compared with the use of commercial ice packs applied to the whole body 34 Evaporative cooling combined with the use of commercial ice packs to the neck, axilla, and groin compared with passive cooling34 and evaporative cooling alone 34 Evaporative cooling compared with the administration of intravenous 0.9% normal saline at 20 C/68.0 F 36 Ice-sheet application (bed sheets soaked in ice water kept at 3 C/37.4 F and towels soaked in ice water kept at 14 C/57.2 F, respectively, to the body compared with passive cooling 24,38 Ice-sheet application (sheets soaked in ice and water at 5 CÀ 10 C; 33.8 FÀ 41.0 F) to the body compared with colder-water immersion (5 CÀ 10 C; 33.8 F À 41.0 F) 33 Commercial ice packs to the neck, groin, and axilla compared with passive cooling 34,35 Commercial ice packs to the whole body compared with passive cooling 34 Fanning alone compared with passive cooling 24,39 Hand-cooling devices compared with passive cooling 46,49,53 A commercial cooling jacket compared with passive cooling 44,46 Various cooling vests compared with passive cooling 24,39,44,…”

Hand and forearm cooling: exploring deep-body cooling in hyperthermic individuals following exercise-induced heating at three different work rates

“…13,14) Subsequent research has not only replicated the thermal phase delays observed via the rectum during the whole-body cooling of hyperthermic individuals, but has also established a cutaneous vascular mechanism to explain those time-dependent observations. 19) Furthermore, that research group unequivocally demonstrated that the cutaneous vascular responses that accompany external cooling are powerfully influenced by the thermal state of the deep-body tissues prior to the initiation of external cooling. 4,20,21) Therefore, during hyperthermia, mild external cooling stimuli were found not to elicit the powerful vasoconstriction that was observed when similar stimuli were applied during normothermia.…”