Respiratory heat and water loss during exercise in patients with asthma. Effect of repeated exercise challenge

A study was performed to investigate the loss of heat and water from the airways during repeated exercise challenge. Twenty-six asthmatic patients performed 6-8 min exercise on a bicycle ergometer at a workload equivalent to 57-85% of their predicted maximum working capacity. Sixteen patients performed two exercise tests separated by 40-52 min. Exercise-induced asthma (EIA) occurred in all patients after initial challenge but eight had significant protection from EIA following a second challenge. This protection was not associated with a reduction in heat and water loss from the airways during exercise. A further 10 patients performed two exercise tests 2-3 h apart. The second test was preceded by the administration of 200 microgram salbutamol aerosol. There was no significant difference between the two tests in loss of heat and water from the airways during exercise. Exercise-induced asthma occurred in all patients after the initial challenge but was inhibited by the salbutamol after the second challenge. Thus the reduction in EIA as a result of a refractory period or in response to aerosol salbutamol is not due to changes in heat and water loss from the airways during exercise.