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* From the Department of Respiratory Medicine (Drs. Al-Rawas and Stevenson, and Mr. Carter) and the University Department of Cardiac Surgery (Drs. Naik and Wheatley), Glasgow Royal Infirmary, Glasgow, Scotland, UK.
Correspondence to: Omar A. Al-Rawas, Department of Medicine, College of Medicine, Sultan Qaboos University, PO Box 35, Postal Code 123, Muscat, Sultanate of Oman; e-mail: orawas{at}squ.edu.om
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.
Design: Descriptive cohort study.
Setting: A regional cardiopulmonary transplant center.
Participants: 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 (
O2),
and carbon dioxide production.
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 transplantation (60.1%; p < 0.05). Although the mean maximal
symptom-limited O2
(O2max) 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
O2max 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 recipients.
Key Words: cardiopulmonary exercise testing • exercise capacity • heart transplantation • pulmonary diffusing capacity • pulmonary function • pulmonary gas exchange
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