Objective: The pulmonary transfer factor for carbon monoxide (TLCO) has been reported to decline following heart transplantation, but the time course of this decline is not well documented. The aim of this study was to define the longitudinal changes in TLCO after heart transplantation.
Methods: Single breath TLCO, lung volumes and expiratory flow rates were prospectively measured in 57 patients (mean age 49 years, range 19-61) before and at least once after heart transplantation. Thirty seven of the 57 patients had four post-transplant assessment which were performed at 6 weeks, 3, 6 and 12 months in 26 patients and at 12, 18, 24 and 36 months in 11 patients. Results were compared with data from 28 normal subjects (mean age 40 years, range 19-61).
Results: Before transplantation there was a mild impairment of lung volumes and expiratory flow rates. At 6 weeks after transplantation, there was a further reduction in the forced expiratory volume in one second, forced vital capacity, residual volume and total lung capacity, but all of these increased in the subsequent measurements to exceed their pre-transplant values at about 1 year after transplantation. Haemoglobin-corrected TLCO was also reduced before transplantation compared to normal controls (74.3% and 98.6% of predicted respectively, P < 0.001). Although TLCO per unit alveolar volume (KCO) was relatively preserved in heart transplant candidates, it was still significantly lower than that of normal controls (92.6% and 105.3% of predicted respectively, P < 0.05). After transplantation, mean haemoglobin-corrected TLCO and KCO declined by 12% and 20% of predicted respectively) with the majority of patients having reductions greater than 10% of predicted. The decline in TLCO and KCO was evident at 6 weeks after transplantation with no further changes in the subsequent measurements.
Conclusions: TLCO is reduced in heart transplant candidates and declines further after heart transplantation despite improvement in lung volumes and airway function. The early and non-progressive nature of TLCO decline suggests an aetiology exerting its effect on TLCO within the first 6 weeks after transplantation.