Effect of hypocapnia on pulmonary mechanics in normal subjects and in patients with chronic obstructive lung disease.

The effect of hypocapnia due to voluntary hyperventilation on the mechanical properties of lungs was studied in normal subjects and in patients with chronic obstructive pulmonary disease. Hypocapnia was associated with an increase in pulmonary resistance (Rl) in 4 of 6 normal subjects and in 7 of 8 patients. The increase in Rl followed the development of hypocapnia within 30 to 60 sec; the response was promptly reversed by removing the hypocapnic stimulus. When expressed as percentage of the control values, the magnitude of the changes in Rl did not differ significantly between the two groups of subjects. Lung compliance (Cdyn) decreased during hypocapnia in 3 of 6 normal subjects and in 6 of 8 patients; the percentage change did not differ significantly between the two groups of subjects. The changes in Cdyn appeared to be similar in their time course to the changes in Rl. The administration of atropine reduced or eliminated the changes in Rl and Cdyn due to hypocapnia. These results indicate that hypoca...