AIRWAY-OBSTRUCTION DURING EXERCISE IN ASTHMA

Airway obstruction (AO) in exercise-induced asthma (EIA) is considered a postexercise phenomenon. However, many with EIA complain of respira tory distress during exercise. We evaluated AO in six asthmatic subjec ts during a short (SX = 6 min) and a long (LX = 20 min) exercise sessi on. We measured peak expiratory Row (PEF) rate, forced expiratory volu me in one second (FEV(1)), and forced expiratory flow at 50% of vital capacity (Vmax(50)) and calculated expiratory and inspiratory pulmonar y resistance (RLe and RU). Rated perceived exertion (RPE) was evaluate d as a measure of dyspnea. All three indices of airflow significantly decreased following SX and LX, but RU and RLe increased. During SX, PE F, FEV(1), and Vmax(50) did not decrease, but RU decreased. During LX, PEF, FEV(1), and Vmax(50) decreased (20.0, 26,0, and 17.7%, respectiv ely), whereas RU and RLe significantly increased (74.0 and 53.0%). Rat ed perceived exertion correlated highly with RU during exercise (r = 0 .95). In summary, there was little or no AO during SX but a frank AO d uring Ut in asthmatic subjects. We conclude that AO occurs during LX a nd that the manifestation of dyspnea is associated with AO during exer cise, as well as in recovery.