Analysis of hyperventilation response in asthmatics.

We have tested seven young adult asthmatics (17-35 years) with two different tests of airway reactivity, i.e., treadmill exercise test and isocapnic hyperventilation test. To estimate the level of respiratory heat loss we standardized environmental conditions so that during these tests patients inhaled compressed air of 23 degrees and 0% of R.H. The level of ventilation during these tests thus determined the respiratory heat loss. It was found that five out of seven tested patients showed dose-response-like relationships between a change in FEF 25-75% (or FEV1) and minute ventilation as measured during exercise or voluntary hyperventilation (r = -.80 to -.97). However, in two patients this relationship could not be established. These two patients had the lowest baseline pulmonary function of the whole group, and by definition they had the most hyperreactive airways. When the change in pulmonary function observed after three to six minutes of isocapnic hyperventilation (both at the same level of minute ventilation) were compared it was found that the six minute test caused only slightly greater changes (P less than 0.01) than the three minute test. It is concluded that in asthmatics the relationship between a decrease in pulmonary function and respiratory heat loss varies among patients.