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

Background: Exercise can induce a bronchodilatation. 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 test conditions: Exercise (EXERC; 30 minutes); 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. All tests were followed by 10 minutes of seated rest in air. A forced vital capacity (FVC) manoeuvre was performed at the start of the test and every 10 minutes thereafter. Forced expiratory volume over 1 second [FEV1] FEV1/FVC, 25, 50 and 75 % maximal expiratory flow during FVC (FEF75, FEF50, FEF25) were also measured. Data were compared using ANOVA, 0.05 alpha level.Results: Rectal temperature (Trec) peaked 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 FEV1 was 4.5 (0.6), 4.6 (0.3), and 4.4 (0.6) L respectively. Trec, 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 IMM40 and EXERC conditions.Conclusion: Increasing deep body temperature, independently, contributes to the increased airflow ascribed to bronchodilatation when exercising.