Modulation of alveolar-capillary sodium handling as a mechanism of protection of gas transfer by enalapril, and not by losartan, in chronic heart failure

Objectives We sought to compare the protective efficacy of enalapril and lo sartan on lung diffusion in chronic heart failure (CHF). Background In CHF, hydrostatic overload causes disruption of the alveolar-c apillary membrane and depression of carbon monoxide diffusion (DCO); enalap ril improves DCO through mechanisms still undefined; and saline infusion in the pulmonary circulation worsens DCO, putatively because of an upregulate d sodium transport to the alveolar interstitium. We investigated whether en alapril modulates sodium handling and whether losartan shares the same prop erties. Methods In 29 patients with CHF, DCO, its membrane diffusion subcomponent ( DM) and right atrial and pulmonary wedge pressures were monitored during sa line infusion, in the control condition, during enalapril therapy (20 mg/da y) for two weeks and after crossover to losartan (50 mg/day) for two weeks (first 20 patients), or after the combination of enalapril with aspirin (32 5 mg/day) for one week (last 9 patients). Results Saline, 150 ml, lowered DCO (-7.9%; p < 0.01) and DM (-9.9%; P < 0. 01) without hydrostatic variations. Responses to 750 ml of saline were qual itatively similar. After treatment with enalapril, baseline DCO (p < 0.01) and DM (p < 0.01) were augmented; after sodium loading, the percent reducti ons of DCO (p < 0.01) and DM (p < 0.01) were comparable to those before it, resulting in higher absolute values. This suggests that the seater the gas conductance improvement with enalapril, the lower the impedance with salin e. Losartan was ineffective on gas transfer at rest and under salt challeng e. Aspirin counteracted the benefits of enalapril. Conclusions In CHF, enalapril protects lung diffusion, possibly through a p rostaglandin-mediated modulation of sodium overfiltration to the alveolar i nterstitium; losartan does not share this ability. (C) 2001 by the American College of Cardiology.