Bronchodilatory Effects on Airway Smooth Muscle in Sedentary vs Active Healthy Subjects

Abstract

Both epinephrine and deep inhalations lead to relaxation of airway smooth muscle following airway constriction. Physical activity has been proposed to lessen airway hyper-responsiveness in health. PURPOSE: The purpose of our study was to determine if bronchodilation following a spasmogen was less in inactive vs physically active healthy subjects. METHODS: Twenty five healthy subjects with a wide range of exercise habits were studied. Physical activity (PA) was determined via the International Physical Activity Questionnaire (IPAQ). Subjects were divided into 3 groups based on their PA (1: 4000 MET min/wk). Subjects were tested during two randomized sessions within 2-weeks. Subjects first performed pulmonary function testing (PFT) and exhaled nitric oxide measurements (eNO). Subjects then breathed a hypertonic (25%) saline solution (HS) from a nebulizer for 20 minutes without deep inhalations followed by PFTs. Subsequently, subjects performed either five maximal deep inhalations (DI) (indirect effect) from residual volume or inhaled 0.44 mg epinephrine (E) (direct effect) followed by PFT measurements on separate days in randomized order. RESULTS: Group 1 (least active) demonstrated greater (P<0.05) airway responsiveness (∼11% decrease in FEV1) following HS inhalation compared to Groups 2 and 3 (∼5% decrease in FEV1). Both E and DI partially or completely restored (P<0.05) the decrease in FEV1 following HS inhalation in all subjects with the greatest (P<0.05) bronchodilation occurring in Groups 2 and 3 (most active). The relationship between the change in FEV1 to PA was related (P<0.05) to both E (r=0.86) and to DI (r=0.75). CONCLUSION: These data suggest that the bronchodilatory response is reduced in sedentary healthy subjects, which may contribute to increased airway hyper-responsiveness in the sedentary population.