Evaluation of pulmonary resistance and maximal expiratory flow measurements during exercise in humans

To evaluate methods used to document changes in airway function during and after exercise, we studied nine subjects with exercise-induced asthma and f ive subjects without asthma. Airway function was assessed from measurements of pulmonary resistance (RL) and forced expiratory vital capacity maneuver s. In the asthmatic subjects, forced expiratory volume in 1 s (FEV1) fell 2 4 +/- 14% and RL increased 176 +/-: 153% after exercise, whereas normal sub jects experienced no change in airway function (RL -3 +/- 8% and FEV1 -4 +/ - 5%). During exercise, there was a tendency for FEV1 to increase in the as thmatic subjects but not in the normal subjects. RL, however, showed a slig ht increase during exercise in both groups. Changes in lung volumes encount ered during exercise were small and had no consistent effect on RL. The sma ll increases in RL during exercise could be explained by the nonlinearity o f the pressure-flow relationship and the increased tidal breathing flows as sociated with exercise. In the asthmatic subjects, a deep inspiration (DI) caused a small, significant, transient decrease in RL 15 min after exercise . There was no change in RL in response to DI during exercise in either ast hmatic or nonasthmatic subjects. When percent changes in RL and FEV1 during and after exercise were compared, there was close agreement between the tw o measurements of change in airway function. In the groups of normal and mi ldly asthmatic subjects, we conclude that changes in lung volume and DIs ha d no influence on RL during exercise. Increases in tidal breathing flows ha d only minor influence on measurements of RL during exercise. Furthermore, changes in RL and in FEV1 produce equivalent indexes of the variations in a irway function during and after exercise.