Alteration of the alveolar-capillary membrane diffusing capacity in chronic left heart disease

During left heart disease, the chronic increase in pulmonary capillary wedge pressure (PCWP) results both in vascular alterations with increased pulmonary vascular resistance (PVR), and in progressive thickening of the alveolar-capillary membrane, which diffusing capacity (Dm) is reduced. However, the total lung diffusing capacity for carbon monoxide (TLco) is inconstantly impaired, depending on the degree of pulmonary congestion. We evaluated the relation between the pulmonary hemodynamic repercussions of chronic heart disease and the 2 components of TLco, i.e., Dm and capillary blood volume. Forty-seven patients with chronic left heart disease (28 with valve disease, 19 with cardiomyopathy) underwent right heart catheterization with determination of PCWP and PVR. Pulmonary function tests, including spirometry, determination of TLco, and of its 2 components (percentage of predicted values) were performed in patients and in 15 healthy subjects. TLco and Dm, but not capillary blood volume, were significantly decreased in patients. Dm was related to PVR (p = 0.0006), and was markedly reduced in patients with high PVR (> or = 3 Wood U): 54 +/- 8% vs 80 +/- 19% in patients with normal PVR (p <0.0001). Dm < or = 66% identified all high PVR patients (sensitivity = 100%, specificity = 77%). Capillary blood volume was related to PCWP (p = 0.02), and was increased in patients with high PCWP (> 15 mm Hg): 126 +/- 30% vs 99 +/- 23% (p <0.01), but with a marked overlap. TLco values, although reduced in patients with high PVR (p <0.001), were not predictive of high PVR or high PCWP. Determination of Dm allows a more accurate detection of pulmonary hypertension complicating chronic left heart disease than the other pulmonary parameters.