Exercise intolerance following heart transplantation - The role of pulmonary diffusing capacity impairment

Study objectives: Although impairment of the diffusing capacity of the lung for carbon monoxide (DLCO) in heart transplant recipients is well-document ed, there are limited data on its impact on exercise capacity in these pati ents. The aim of this study was to determine the effect of DLCO reduction o n exercise capacity in heart transplant recipients. Design: Descriptive cohort study. Setting: A regional cardiopulmonary transplant center. Participants: Twenty-six heart transplant recipients who were studied befor e and after transplantation compared with 26 healthy volunteers. Measurements: Spirometry and static lung volumes were measured using body p lethysmogaphy, DLCO was measured using the single-breath technique, and pro gressive cardiopulmonary exercise was performed using a bicycle ergometer, continuous transcutaneous blood gas monitoring, and on-line analysis of min ute ventilation, oxygen uptake ((V) over dot O-2), and carbon dioxide produ ction. Results: Before transplantation, the mean percent predicted for hemoglobin- corrected DLCO was reduced in patients (73.2%) compared to healthy control subjects (98.8%; p < 0.001) and declined significantly after transplantatio n (60.1%; p < 0.05). Although the mean maximal symptom-limited (V) over dot O-2 ((V) over dot O(2)max) increased after transplantation (increase, 41.3 to 48.6% of predicted; p < 0.05), it remained substantially lower than nor mal (92.9%; p < 0.001), There was a significant correlation between DLCO an d (V) over dot O(2)max after transplantation (r = 0.61; p = 0.001), but not before transplantation (r = 0.09; p = 0.66). DLCO was also inversely corre lated with other respiratory responses to exercise, including the following : the ventilatory response to exercise (r = -0.44; p < 0.05); dead space to tidal volume ratio (r = -43; p < 0.05); and the alveolar-arterial oxygen g radient (r = -0.45; p < 0.05), but there was no correlation between any of these variables and DLCO before transplantation. Conclusion: DLCO reduction after heart transplantation appears to represent persistent gas exchange impairment and contributes to exercise limitation in heart transplant recipients.