Exercise-induced dehydration alters pulmonary function but does not modify airway responsiveness to dry air in athletes with mild asthma

Background: Local airway water loss is the main physiological trigger for exercise-induced bronchoconstriction (EIB). Aim: To investigate the effects of whole-body water loss on airway responsiveness and pulmonary function in athletes with mild asthma and/or EIB. Methods: Ten recreational athletes with a doctor diagnosis of mild asthma and/or EIB completed a randomized, cross-over study. Pulmonary function tests (spirometry, whole-body plethysmography and diffusing capacity for carbon monoxide [DLCO]) were conducted before and after three conditions: i) 2 h exercise in the heat with no fluid intake (dehydration); ii) 2 h exercise with ad libitum fluid intake (control); and iii) time-matched rest period (rest). Airway responsiveness was assessed 2 h post-exercise/rest via eucapnic voluntary hyperpnea (EVH) to dry air. Results: Exercise in the heat with no fluid intake induced a state of mild dehydration, with a mean body mass loss of 2.3±0.8% (SD). After EVH, airway narrowing was not different between conditions: median (interquartile range) maximum fall in forced expiratory volume in 1 sec was 13 (7-15)%, 11 (9-24)% and 12 (7-20)% in the dehydration, control and rest conditions, respectively. Dehydration caused a significant reduction in forced vital capacity (300±190 ml, P=0.001) and concomitant increases in residual volume (260±180 ml, P=0.001) and functional residual capacity (260±250 ml, P=0.011), with no change in DLCO. Conclusion: Mild exercise-induced dehydration does not exaggerate airway responsiveness to dry air in athletes with mild asthma/EIB, but may affect small airway function.