Do voluntary changes in inspiratory-expiratory ratio prevent exercise-induced asthma?

It is often admitted that heat exchange in the airways is a major cause of exercise-induced asthma. Because a decrease in the inspiratory time/expiratory time ratio (TI/TE) decreases these exchanges, we postulated that it might decrease bronchoconstriction as well. Twenty-four asthmatic children, divided into three groups, underwent two exercise provocation tests, 24 hours apart (outdoor running for 6 min). The first test was identical for all the subjects. In the second test, the first group did not receive any instruction concerning breathing pattern. The second group was instructed to adopt equal inspiratory and expiratory times (TI/TE = 1). The third group had to adopt an expiratory time three times longer than inspiratory time (TI/TE = 1/3). The three groups displayed similar pulmonary function tests (FEV1 and FVC), cardiac frequency, and running performances. However, FEV1 significantly improved in the second session. This suggested that familiarization with the task and related psychological factors may influence asthma more than voluntary changes in TI/TE.