Background: Cardiopulmonary exercise testing (CPET) with blood gas analysis may be helpful when there is a discrepancy between clinical findings and physiologic tests at rest. The aim of this study was to examine the added value of CPET compared to the measurement of the diffusing capacity of the lung for carbon monoxide (DLCO) in detecting impaired pulmonary gas exchange in sarcoidosis patients.
Methods: The clinical records of 160 (age = 41.3 ± 10.0 years; number of females = 63) sarcoidosis patients referred to the former MUMC ild care center were retrospectively reviewed. Patients performed a symptom-limited incremental exercise test with blood gas analysis on a bicycle ergometer. DLCO was measured by the single-breath method.
Results: DLCO (mean = 83.2 ± 18.0 %) below 80 % of predicted was demonstrated by 38 % of the sarcoidosis patients in our sample. Of the patients with normal DLCO (n = 99, 61.9 %), the P(A-a)O(2) at maximal exercise [P(A-a)O(2)max] was moderately increased (>2.5 kPa) in 69.7 % and excessively increased (>4.7 kPa) in 18.2 %. Pulmonary gas exchange impairment (PGEI) was more obvious in patients with lower DLCO values. A DLCO value below 60 % of predicted indicated substantial gas exchange impairment. PaO(2) at rest, DLCO, and FVC as a percentage of predicted and radiographic staging predicted 40 % of the PGEI at maximal exercise.
Conclusion: A substantial number of the symptomatic sarcoidosis patients with normal DLCO appeared to have PGEI at maximal exercise, suggesting that normal DLCO at rest is an inappropriate predictor of abnormal pulmonary gas exchange during exercise. CPET appeared to offer added value in detecting impaired gas exchange during exercise in sarcoidosis patients with unexplained disabling symptoms.