Study objectives: Although impairment of the diffusing
capacity of the lung for carbon monoxide (Dlco) in heart
transplant recipients is well-documented, there are limited data on its
impact on exercise capacity in these patients. The aim of this study
was to determine the effect of Dlco reduction on exercise
capacity in heart transplant recipients.
Descriptive cohort study.
Setting: A regional
cardiopulmonary transplant center.
Twenty-six heart transplant recipients who were studied before and
after transplantation compared with 26 healthy volunteers.
Measurements: Spirometry and static lung volumes
were measured using body plethysmography, Dlco
was measured using the single-breath technique, and progressive
cardiopulmonary exercise was performed using a bicycle ergometer,
continuous transcutaneous blood gas monitoring, and on-line analysis of
minute ventilation, oxygen uptake (V̇o2),
and carbon dioxide production.
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 transplantation (60.1%; p < 0.05). Although the mean maximal
(V̇o2max) increased after transplantation
(increase, 41.3 to 48.6% of predicted; p < 0.05), it remained
substantially lower than normal (92.9%; p < 0.001). There was a
significant correlation between Dlco and
V̇o2max after transplantation
(r = 0.61; p = 0.001), but not before
transplantation (r = 0.09; p = 0.66).
Dlco was also inversely correlated 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 gradient (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