The alveolar-capillary membrane diffusing capacity and the pulmonary capillary blood volume in heart transplant candidates

Objectives-To determine the mechanism of impairment of pulmonary transfer f actor for carbon monoxide (TLCO) in heart transplant candidates, as this is the most common lung function abnormality. Setting-Regional cardiopulmonary transplant centre. Methods-TLCO and its components (the diffusing capacity of the alveolar-cap illary membrane (D-M) and the pulmonary capillary blood volume (V-C)) were measured using the Roughton and Forster method and the single breath techni que in 38 patients with severe chronic heart failure awaiting heart transpl antation (mean age 51 years, range 19 to 61; mean left ventricular ejection fraction 12.8%). Results were compared with data from 26 normal subjects ( mean age 47 years, range 27 to 62). Results-Mean per cent predicted TLCO, D-M, and V-C were significantly reduc ed in patients (69.9%, 81.4%, and 80.2% of predicted, respectively) compare d with controls (97.7%, 100.1%, and 102.3% of predicted, respectively, p < 0.001), The relative contribution of the two components of TLCO in patients was similar to that of normal subjects, with each component accounting for approximately 50% of the total resistance to diffusion (1/TLCO). Conclusions-TLCO impairment in patients with severe chronic heart failure a waiting heart transplantation results from a proportionate reduction in bot h D-M and V-C, suggesting a significant disturbance of the pulmonary vascul ar bed.