Action of isoprenaline on the mechanical properties of lungs and airways in healthy people and patients with obstructive lung diseases.

Lung volumes, maximal expiratory flows, pulmonary resistance and static recoil pressure-volume curves were measured before and after inhalation of isoprenaline in four groups of subjects: heqlthy patients with mild and severe chronic bronchitis and asthmatics. The observed changes were qualitatively similar in the four groups. Whereas total lung capacity and dynamic compliance were not influenced, there was an increase in vital capacity (not in healthy subjects and mild bronchitics), in FEV1, in maximal expiratory flows and a decrease in pulmonary resistance. The static recoil pressure-volume relationship was shifted to the left over its ascending part. The effect of isoprenaline tended to be larger in patients. Among the latter, the increase of vital capacity was especially pronounced in the severe bronchitics, whereas the maximal flows increased most in asthmatics. We suggest that the influence of isoprenaline on maximal flows results from a bronchodilation, associated with an increased collapsibility of the central intrathoracic airways, whereas the influence of VC might reflect a delayed onset of small airway closure.