Mechanisms of pulmonary transfer factor decline following heart transplantation

Objective: Although the decline in the pulmonary transfer factor (TLCO) fol lowing heart transplantation is well documented, the causes and mechanisms of this decline remain unknown. The aim of this study was to determine the relative contribution of each of TLCO components (the diffusing capacity of the alveolar-capillary membrane (D-M), the pulmonary capillary blood volum e (V-C) and haemoglobin concentration) to TLCO reduction in heart transplan t recipients. Methods: TLCO and its components were measured in 75 heart tr ansplant recipients (mean age 48 years, range 19-61) between 6 weeks and 36 months after transplantation using the Roughton and Forster method and the single-breath technique. Results were compared with data from 38 heart tra nsplant candidates (mean age 51 years, range 34-61) and 26 normal subjects (mean age 47 years, range 27-62). Results: The mean percentage predicted TL CO was reduced in recipients compared to candidates (56.9 and 69.9%, respec tively, P < 0.001) and both were lower than normal controls (97.7%, P(0.001 ). The mean percent predicted V-C was also reduced in recipients compared t o candidates (52.8% vs. 80.2 (4.2)%, P < 0.001) which was also lower than n ormal subjects (102%, P < 0.001). D-M was equally reduced in recipients and candidates (77.7 and 81.4%, respectively, P = 0.48) compared to normal sub jects (100.0%, P < 0.001). Correction for haemoglobin concentration increas ed TLCO in recipients to 63.5% (P < 0.001), but it remained lower than haem oglobin-corrected TLCO in candidates (71.1%, P < 0.001). in recipients, the intra-capillary resistance (1/theta V-C) formed 60% of the total resistanc e to CO transfer (1/TLCO) compared to 50% in candidates and normal subjects . Conclusions: TLCO decline following heart transplantation is due to an in crease in the intra-capillary resistance, and this appears to be due to a c ombination of anaemia and reduced pulmonary capillary blood volume, with th e diffusing capacity of the alveolar-capillary membrane remaining unchanged . (C) 2000 Elsevier Science B.V. All rights reserved.