Angiotensin-converting enzyme inhibition facilitates alveolar-capillary gas transfer and improves ventilation-perfusion coupling in patients with left ventricular dysfunction

Objective: The backward effects of left ventricular dysfunction include alterations in alveolar-capillary gas transfer and ventilation-perfusion coupling. Because the angiotensin-converting enzyme (ACE) is highly concentrated in the vascular endothelium of the lungs, we examined whether ACE inhibitors may influence the pulmonary function in patients with congestive heart failure. Methods: In 20 patients with idiopathic cardiomyopathy, pulmonary function and exercise capacity were evaluated at baseline and 6 and 12 months after treatment with enalapril (10 mg twice a day) was started. The study also included 19 age- and sex-matched control subjects with mild primary hypertension and normal left ventricular function who were given enalapril as a standard treatment of high blood pressure. Results: In congestive heart failure, forced expiratory volume in 1 second, vital capacity, and total lung capacity did not vary significantly with enalapril; alveolar-capillary diffusion of carbon monoxide (DL(CO)) increased toward normal; exercise tolerance time, peak exercise oxygen uptake (peak VO ₂), minute ventilation and tidal volume (peak VT) also increased; and the ratio of volume of dead space (VD) to VT (peak VD/VT) at peak exercise reduced. Changes in peak VO ₂ showed a direct correlation with those in DL(CO) and an inverse correlation with those in peak VD/VT. Results at 6 and 12 months were comparable. Enalapril did not affect these variables in the control population. Conclusions: In patients with idiopathic cardiomyopathy heart failure, but not in control subjects, gas transfer and ventilation- perfusion improved with ACE inhibition. These pulmonary changes may contribute to the associated increase in exercise tolerance.