Chest
Clinical InvestigationsPulmonary FunctionMembrane and Capillary Blood Components of Diffusion Capacity of the Lung for Carbon Monoxide in Pulmonary Sarcoidosis: Relation to Exercise Gas Exchange
Section snippets
Patients
Twenty-four patients with pulmonary sarcoidosis histologically confirmed were prospectively studied in our department of physiology between February 1999 and June 2000. All the patients had pulmonary infiltration shown on chest radiography and were classified according to American Thoracic Society staging.18 Group 1 (n = 15) included patients with radiographic stages 2 or 3 (no evidence of pulmonary fibrosis), and group 2 (n = 9) included patients with radiographic stage 4 (pulmonary fibrosis).
Pulmonary Function
Results of function tests are summarized in Table 1. Both groups demonstrated a moderate reduction in lung volumes and airflows. Dlco was severely reduced in the two groups (63 ± 17% of predicted in group 1, p < 0.05; 64 ± 16% of predicted in group 2, p < 0.05). The actual value of FEV1/VC was smaller in group 2 than in group 1, but this difference disappeared when FEV1/VC was expressed in percentage of predicted value. Since FEV1/VC decreases with age, this finding likely reflects the age
DISCUSSION
The present study provides the first comprehensive analysis of the relation between the two components of Dlco—Dm and Vc—and exercise gas exchange in pulmonary sarcoidosis. It clearly shows that the reduction of Dm mostly accounts for the decrease of resting Dlco, and that this parameter is the best resting predictor of gas exchange abnormalities during exercise.
In sarcoidosis, alteration of Dlco may reflect changes in gas exchange area, barrier thickness, and ventilation-perfusion-diffusion
CONCLUSION
In conclusion, this study demonstrates that in sarcoidosis without or with pulmonary fibrosis, the decrease of Dlco is mainly related to its Dm component and that Dm is the best predictor of abnormal gas exchange at exercise. Vc is only mildly altered, probably because of vascular recruitment at rest. Vascular involvement in patients with sarcoidosis might be more accurately approached by analyzing Dlco and its two components at exercise.
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