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

In contrast to skeletal muscle function and temperature, the contribution of change in respiratory muscle temperature is usually ignored when considering the changes in lung function during exercise. We examined whether an increase in deep body temperature, independently, contributes to increases in ventilatory flow indicative of bronchodilatation.

Using 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 minutes cycle ergometry, 70 rpm, 70% of age-predicted max heart rate); 40 °C water immersion (IMM40; 30 minutes) to passively raise rectal temperature (Trec); and 35°C immersion (IMM35; 30 minutes) a thermoneutral control for IMM40. A forced vital capacity (FVC) manoeuvre was performed at the start of the test and every 10 minutes thereafter. Forced expiratory volume in one second [FEV₁] FEV₁/FVC, 25, 50 and 75 % maximal expiratory flow during FVC (FEF75, FEF50, FEF25) were also measured. Data were analysed using a repeated measures two-way ANOVA, with a 0.05 alpha level.

Trecpeaked after 30 minutes in the EXERC (mean [SD] 38.0 [0.3] °C) and IMM40 (38.2 [0.2] °C) conditions and were higher (P<0.05) than that those at the corresponding time in the thermoneutral condition (37.2 [0.2] °C). At this time mean (SD) FEV₁ was 4.5 (0.6), 4.6 (0.3), and 4.4 (0.6) L respectively. T_rec, FEV₁, and FEV₁/FVC were greater in the IMM40 and EXERC conditions compared to the IMM35 condition. Interaction effects were evident for FEF50 and FEF75 (P<0.05), being higher in the IMM40 and EXERC conditions.

Raised deep body temperature, independently, contributes to the increased airflow ascribed to bronchodilatation when exercising.