Impedance to gas transfer across the alveolar-capillary membrane in congestive heart failure

One of the consequences of an elevation of the pulmonary capillary pressure in chronic heart failure is the occurrence of structural and functional changes at the level of the alveolar-capillary interface. These changes are called "stress failure" of the membrane, and consist of thickening of the interstitium, increase in capillary permeability to water and ions, and disruption of local regulatory mechanisms for gas exchange. Functional correlates are an augmented impedance to gas transfer (DL), a reduction in the alveolar-capillary membrane conduction (DM) and an increase in the volume of the pulmonary capillary blood (VC). DM and VC are the two subcomponents of DL. DM has been identified as the strongest respiratory predictor of oxygen uptake at peak exercise in patients with chronic heart failure, suggesting that impeded lung diffusion may significantly contribute to exercise limitation and ventilatory abnormalities. The evidence relating to the pathophysiological and clinical significance of the impairment in lung diffusion capacity in patients with chronic heart failure, as well as the response to treatment are the main subjects of this review.