Influence of ACE-inhibition on salt-mediated worsening of pulmonary gas exchange in heart failure

Aims In congestive heart failure (CHF), pulmonary gas exchange, as evaluated by carbon monoxide diffusion (DLCO), is impaired. ACE-inhibition improves DLCO. Infusion of saline worsens DLCO, because of upregulated sodium and water transport to the alveolar interstitium, which thickens the alveolar-capillary interface and lengthens the diffusion path for gas exchange. We investigated whether enalapril can readjust the capillary permeability to sodium. Methods In 10 NYHA class II-III CHF patients, we measured DLCO, its two subcomponents (V-C, capillary blood volume available for gas exchange, and DM, alveolar-capillary membrane diffusion), left and right ventricular filling pressures, plasma noradrenaline, aldosterone and renin activity, at baseline and following saline infusion in the main pulmonary artery stem, before and after 1 week enalapril treatment (20 mg daily). Results Saline (150 mi) significantly reduced DLCO (-9.1%) and D-M (-9.8%) and augmented V-C (+10.7%). Responses to 750 mi saline were somewhat greater and qualitatively similar. Enalapril produced a significant improvement of DLCO and D-M at rest as well as after saline, that was not associated with variations in ventricular filling pressures, cardiac output and left ventricular ejection fraction, and was not accounted for by humoral changes. Conclusions In CHF, ACE-inhibition attenuates the deterioration of pulmonary gas transfer produced by saline infusion, suggesting an ability to readjust the upregulated sodium transport across the pulmonary microvascular endothelium.