Changes in lung function during exercise are independently mediated by increases in deep body temperature

BACKGROUND: This study examined whether an increase in deep body temperature contributes to increases in ventilatory flow indicative of bronchodilatation. METHOD: The study employed a within-participant repeated measures design. Nine participants (mean (SD): age 22 (3) years; height 177.7 (8.3) cm; mass 80.2 (19.1) kg) completed three conditions: exercise (EXERC; 30 min); 40°C water immersion (IMM40; 30 min) to passively raise rectal temperature (T(re)) and 35°C immersion (IMM35; 30 min) asa thermoneutral control for IMM40. A forced vital capacity (FVC) manoeuvre was performed at the start of the test and every 10 min thereafter. Forced expiratory volume in 1 s (FEV(1)), FEV(1)/FVC, 25%, 50% and 75% maximal expiratory flow during FVC (forced expiratory flow (FEF)25, FEF50, FEF75) were also measured. Data were compared using a repeated measures two-way analysis of variance, with a 0.05 α level. RESULTS: Rectal temperature (T(re)) peaked after 30 min in the EXERC (mean (SD) 38.0 (0.3)°C) and IMM40 (38.2 (0.2)°C) conditions and both were higher (p<0.05) than at the corresponding time in the thermoneutral condition (37.2 (0.2)°C). At this time, FEV(1) was 4.5 (0.6), 4.6 (0.3) and 4.4 (0.6) L, respectively. T(re), FEV(1) and FEV(1)/FVC were greater in the IMM40 and EXERC conditions compared with the IMM35 condition. Interaction effects were evident for FEF50 and FEF75 (p<0.05), being higher in IMM40 and EXERC conditions. CONCLUSION: Increasing deep body temperature, independently, contributes to the increased airflow ascribed to bronchodilatation when exercising.