Sudomotor activity and heat balance with serial cooling and heating of thermosensors in the esophagus and stomach

Abstract

This study assessed heat balance parameters and characterized transient sweating responses on the forehead following graded changes in local temperature of the esophagus and stomach from ingesting water of different temperatures. Seven male participants cycled for 75‐min in a temperate environment while ingesting four 3.2 mL·kg−1 boluses of either 1.5°C, 10°C, 37°C or 50°C water, 5‐min before, and 15, 30 and 45‐min after the start of exercise at 50% VO2max. Whole‐body sweat loss (WBSL), rectal temperature (Tre), mean skin temperature (Tsk) and local sweat rate on the forehead (SRhead) were measured throughout. Evaporative heat loss from sweating (Esk), respiratory heat loss, dry heat losses and heat exchange with ingested water were subsequently calculated to estimate net body heat storage (S). Despite no differences in Tre or Tsk, the onset time for sudmotor activity on the forehead was significantly greater with declining fluid temperature (P<0.05), and both mean SRhead throughout exercise and WBSL was significantly lower with 1.5°C compared to 50°C water ingestion (P=0.002). Values for S were significantly greater following 1.5°C water ingestion relative to 50°C (P=0.033), indicating a disproportionate reduction of thermoregulatory sweating, and therefore Esk, relative to the internal heat transfer with 1.5°C water. It is proposed that these data present evidence of independent thermoafferent processes arising from changes in local temperature of the esophagus and/or stomach.Funding for the study was provided by a NSERC discovery grant.