Pulmonary function in status asthmaticus: effect of therapy.

In 11 patients with bronchial asthma, lung volumes, FEV, PaO, and lung diffusing capacity (single breath CO method) were measured in status asthmaticus and after recovery. Ventilatory capacity improved following therapy. The improvement was associated with a rise in vital capacity and a fall in residual volume, but the total lung capacity might either decrease, increase or remain unchanged. A decreased value of PaO was found in all patients in status asthmaticus. After treatment PaO increased in all patients. In two of them PaO increased despite the unchanged values of the other parameters of pulmonary function. The improvement of PaO after treatment is considered to be the result of adjustment of perfusion to ventilation. The lung diffusing capacity was below normal values in three patients before treatment. After treatment the diffusing capacity increased in six patients. The diffusion constant, although within the normal range in status asthmaticus, increased after treatment in one and decreased in three other patients. The decreased diffusing capacity in status asthmaticus is the consequence of a reduced effective alveolar volume due to uneven distribution of ventilation. The changes observed in the diffusion constant following corticotherapy are ascribed to a dependence of this constant on the different level of the alveolar volume at which the single breath test is performed.