An assessment of the pulmonary response to exercise in asthma and an analysis of the factors influencing it.

Abstract

The purposes of this study were to determine (1) whether an exercise stimulus could be repeatedly applied to a group of asthmatics and normal control subjects with reproducible metabolic and ventilatory consequences; (2) the effect of this stimulus on multiple aspects of pulmonary mechanics in both groups; (3) the degree of within- and between-day variation in response and the factors influencing it; and (4) the effects of pretreatment with disodium cromoglycate. Airway resistance, specific conductance, total lung capacity and its subdivisions, and forced expiratory volumes and flow rates were measured in 21 asthmatics and 8 normal control subjects before and after treadmill exercise. Minutes ventilation, tidal volume, repiratory frequency, oxygen consumption, carbon dioxide production, heart rate, and end-tidal carbon dioxide tensions were measured during exercise and recovery. The asthmatics were studied twice datly on 2 separate days. Disodium cromoglycate was administered to the asthmatics before the fourth trial. The control subjects were studied twice on the same day without any interventions. There was no difference between exercise trials as measured by any of the gas exchange variables and there were no within-day differences in baseline pulmonary mechanics in either group. In contrast to the control group, all of the asthmatics had increasing airway obstruction after the exercise challenge. There were no between -day differences in the baseline data or response to exercise in the asthmatics except that the mechanical response was less after disodium cromoglycate, which suggests that mediator release played a part. Although as a group the stimulus and response were reproducible, when data of each trial were related to the type and degree of baseline dysfunction there was a direct relationship between pre-existing obstruction and magnitude of response. This suggests that exercise-induced asthma is not an all-or-none event, but rather a continuum of responses profoundly influenced by the pre-challenge state of the airways.