Carbon monoxide-diffusing capacity in intravenous drug abusers: the effect of cigarette smoking and HIV infection

A reduction in the Dco has been frequently found in intravenous drug addicts (IVDAs) and in subjects with HIV infection. Since also cigarette smoking decreases Dco, we studied a group of street IVDAs, who did not show respiratory symptoms and/or infiltrates on chest x-ray film. Sixty-two patients were presently smoking, 2 had never smoked. Twenty-seven were HIV-negative and 37 HIV-positive. Mean values for Dco (percent of predicted values) were 78 +/- 16.4 in HIV-positives compared to 97.9 +/- 17.6 in HIV-negatives (p < 0.0001) using smoking specific equations and 71.8 +/- 15.4 in HIV-positives compared to 80.7 +/- 13.4 (p < 0.0001) using non-smokers equations. Dco was < 80 percent in 19 of 35 (54.3%) HIV-positive subjects and in 4 of 26 (15.4%) HIV-negative subjects (p < 0.009) using predicted values for smokers, and in 28 of 35 (80%) HIV-positive subjects and in 6 of 26 (23.1%) HIV-negative subjects (p < 0.0001) using predicted values for non-smokers. These data suggest that Dco alterations observed in HIV-positive subjects are due, in absence of respiratory symptoms and/or chest x-ray abnormalities, to an interstitial pneumopathy due to HIV or to a subclinical pulmonary disease. We conclude that the knowing of smoking in IVDAs is useful, but the knowing of seropositivity is much more important, since a marked reduction of Dco in these subjects suggests an HIV-related lymphocytic alveolitis, an opportunistic infection or a malignancy.