Exercise Intolerance Following Heart Transplantation

Although impairment of the diffusingcapacity of the lung for carbon monoxide (Dlco) in hearttransplant recipients is well-documented, there are limited data on itsimpact on exercise capacity in these patients. The aim of this studywas to determine the effect of Dlco reduction on exercisecapacity in heart transplant recipients. Descriptive cohort study. A regionalcardiopulmonary transplant center. Twenty-six heart transplant recipients who were studied before andafter transplantation compared with 26 healthy volunteers. Spirometry and static lung volumeswere measured using body plethysmography, Dlcowas measured using the single-breath technique, and progressivecardiopulmonary exercise was performed using a bicycle ergometer, continuous transcutaneous blood gas monitoring, and on-line analysis ofminute ventilation, oxygen uptake (Vo2),and carbon dioxide production. Beforetransplantation, the mean percent predicted for hemoglobin-correctedDlco was reduced in patients (73.2%) compared to healthycontrol subjects (98.8%; p < 0.001) and declined significantlyafter transplantation (60.1%; p < 0.05). Although the mean maximalsymptom-limited Vo2(Vo2max) increased after transplantation(increase, 41.3 to 48.6% of predicted; p < 0.05), it remainedsubstantially lower than normal (92.9%; p < 0.001). There was asignificant correlation between Dlco and, Vo2max after transplantation(r = 0.61; p = 0.001), but not beforetransplantation (r = 0.09; p = 0.66).Dlco was also inversely correlated with other respiratoryresponses to exercise, including the following: the ventilatoryresponse to exercise (r = −0.44; p < 0.05); deadspace to tidal volume ratio (r = −43; p < 0.05);and the alveolar-arterial oxygen gradient (r = −0.45;p < 0.05), but there was no correlation between any of thesevariables and Dlco before transplantation. Dlco reduction after hearttransplantation appears to represent persistent gas exchange impairmentand contributes to exercise limitation in heart transplantrecipients.