Evidence of viscerally-mediated cold-defence thermoeffector responses in man

Sudomotor activity is modified by both warm and cold fluid ingestion during heat stress, independently of differences in core and skin temperatures, suggesting independent viscerally-mediated modification of thermoeffectors. The purpose of the present study was to determine whether visceral thermoreceptors modify shivering responses to cold stress. Ten males (27 ± 5y, 1.73 ± 0.06 m, 78.4 ± 10.7 kg) underwent whole-body cooling via 5 °C water perfusion-suit, on four occasions, to induce a steady-state shivering response, at which point two aliquots of 1.5 ml/kg (SML) and 3.0 ml/kg (LRG), separated by 20- min, of either 7°C, 22°C, 37°C or 52°C water were ingested. Rectal, mean skin and mean body temperature (Tb), electromyographic activity (EMG), metabolic rate (M) and whole-body thermal sensation on a visual analogue scale (WBTS) ranging from 0 mm [very cold] to 200 mm [very hot] were all measured throughout. Tb was not different between all fluid temperatures following SML (7°C:35.7 ± 0.5°C, 22°C:35.6 ± 0.5°C, 37°C:35.5 ± 0.4°C, 52°C:35.5 ± 0.4°C; P = 0.27) or LRG (7°C:35.3 ± 0.6°C, 22°C:35.3 ± 0.5°C, 37°C:35.2 ± 0.5°C, 52°C:35.3 ± 0.5°C; P = 0.99) fluid ingestion. With SML ingestion, greater metabolic rate and cooler thermal sensations were observed with 7°C (M:179 ± 55 W, WBTS:29 ± 21 mm) compared to 52°C (M:164 ± 34 W, WBTS:51 ± 28 mm; all P < 0.05) ingestion. With LRG ingestion, compared to shivering and thermal sensations with 37 °C ingestion (M:215 ± 47 W, EMG:3.9 ± 2.5%MVC, WBTS:33 ± 2 mm) values were different (all P < 0.05) following 7°C (M:269 ± 77 W, EMG:5.5 ± 0.9%MVC, WBTS:14 ± 12 mm), 22°C (M:270 ± 86 W, EMG:5.6 ± 1.0%MVC, WBTS:18 ± 19 mm) and 52°C (M:179 ± 34 W, EMG:3.3 ± 2.1%MVC, WBTS:53 ± 28 mm) ingestion. In conclusion, ingesting 52°C fluids decreased shivering and the sensation of coolness, whereas 22°C and 7°C fluids increased shivering and sensations of coolness to similar levels, independently of core and skin temperature.