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 (Tre) 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 (FEV1), FEV1/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 (Tre) 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, FEV1 was 4.5 (0.6), 4.6 (0.3) and 4.4 (0.6) L, respectively. Tre, FEV1 and FEV1/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.