Membrane and capillary blood components of diffusion capacity of the lung for carbon monoxide in pulmonary sarcoidosis: relation to exercise gas exchange.
BACKGROUND
Resting pulmonary diffusing capacity of the lung for carbon monoxide (DLCO) is known to be the best predictor of arterial desaturation during exercise in patients with sarcoidosis. However, the relative contribution of each of the two components of DLCO-alveolar membrane diffusing capacity (Dm) and pulmonary capillary blood volume (Vc)-remains unclear.


OBJECTIVE
To evaluate which component is responsible for the decrease of resting DLCO in patients with sarcoidosis, and to determine which resting pulmonary function test, including Dm and Vc, is the best predictor of gas exchange abnormalities during submaximal exercise.


METHODS
Prospective analysis of patients referred to our department of respiratory medicine.


METHODS
Twenty four patients with pulmonary sarcoidosis were separated into two groups according to chest radiographic findings: group 1, stages 2 and 3 (n = 15); group 2, stage 4 (n = 9). All the patients completed pulmonary function tests (flows, volumes, single-breath DLCO, transfer coefficient [Ka], Dm, Vc) and submaximal exercise (two steady-state levels of mild and moderate exercise corresponding respectively to a target oxygen consumption of approximately 10 to 15 mL/min/kg).


RESULTS
DLCO was reduced in the two groups (group 1, 63 +/- 16% of predicted; group 2, 64 +/- 16% of predicted). Dm was severely decreased (group 1, 58 +/- 24% of predicted; group 2, 51 +/- 15% of predicted), whereas Vc was unchanged or only mildly decreased (group 1, 81 +/- 18% of predicted; group 2, 85 +/- 28% of predicted). Whatever the group of patients and the exercise level, Dm and DLCO were the strongest predictors (p < 0.001) of gas exchange abnormalities. Ka or volumes were weak predictors, and Vc or flows were not related with exercise gas exchange.


CONCLUSIONS
This study demonstrates that a decrease in Dm mostly accounts for resting DLCO reduction, and that Dm as well as DLCO are highly predictive of gas exchange abnormalities at exercise in patients with sarcoidosis.
Lamberto
Christine
C
Department of Physiology, Assistance Publique/Hôpitaux de Paris, Hôpital Avicenne, Bobigny, France. christine.lamberto@avc.ap-hop-paris.fr
Nunes
Hilario
H
Le Toumelin
Philippe
P
Duperron
Florence
F
Valeyre
Dominique
D
Clerici
Christine
C
D000328:Adult; D002196:Capillaries; D002248:Carbon Monoxide / Q000032:analysis / Q000097:blood*; D005080:Exercise Test; D005260:Female; D006801:Humans; D008297:Male; D008566:Membranes; D008875:Middle Aged; D015999:Multivariate Analysis; D011237:Predictive Value of Tests; D011336:Probability; D011379:Prognosis; D011446:Prospective Studies; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012129:Respiratory Function Tests; D012146:Rest; D012494:Sampling Studies; D017565:Sarcoidosis, Pulmonary / Q000175:diagnosis* / Q000378:metabolism; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
D002248:Carbon Monoxide