Relationship between impaired pulmonary diffusion and cardiopulmonary exercise capacity after heart transplantation

Study objectives: Diffusion impairment and reduced performance in cardiopul monary exercise testing (CPX) have been found in patients after heart trans plantation. The pathogenesis of these abnormalities is unclear. In particul ar, the contribution of pulmonary interstitial changes has not yet been ver ified. Design: We analyzed pulmonary function tests, high-resolution CT (HRCT), ec hocardiography, left heart catheterization, and CPX in transplanted patient s. Patients: Forty long-term survivors were studied at a median of 47 months ( range, 12 to 89 months) after heart transplantation. Results: Diffusion was impaired in 40% (transfer factor for carbon monoxide ) or 82.5% (carbon monoxide transfer coefficient) of the patients. Diffusio n impairment was caused by a decreased diffusing capacity of the alveolar c apillary membrane in 89% and/or by a decreased blood volume of the alveolar capillaries in 46% of cases. In five patients (12.5%), CT revealed interst itial lung changes. These patients did not have different values of diffusi on capacity, Maximal oxygen uptake and ventilatory efficiency during exerci se (minute ventilation/carbon dioxide output slope) were impaired in 92% an d 46% of the cases, respectively. Conclusions: Our data show that the diffusion abnormalities are caused by a n impaired diffusion status of the alveolar capillary membrane, Interstitia l changes detectable in HRCT were found not to be involved in this process. The reduced performance in CPX in our long-term survivors is caused by pul monary perfusion abnormalities and low tidal volume, which is due to the de conditioning of respiratory muscle, rather than by interstitial changes or diffusion abnormalities.