Acute effect of cigarette smoking on the carbon monoxide diffusing capacity of the lung.

To determine the acute effect of smoking on DLCO, we studied 12 smokers (mean age, 36 yr; range, 19 to 52 yr, six men and six women) before and after they had smoked as many cigarettes as they could (mean, 6.0; SD, 1.9) over a period of 1 h. Blood COHb was estimated using a rebreathing-breathholding technique after a vital capacity inhalation of O2. Capillary blood volume (VC) was determined from DLCO performed at inspired O2 concentrations of 25 and 90%. DLCO (in ml/min/mm Hg) corrected for COHb back pressure decreased from 22.5 (SD, 6.6) before smoking to 21.0 (SD, 6.6) after smoking (p = 0.003). After correction for the "anemia effect" of COHb, DLCO still significantly decreased, from 22.8 (SD, 6.3) before smoking to 21.8 (SD, 6.4) after smoking p = 0.01). VC (corrected for the reduction in hemoglobin by COHb) was 52.0 (SD, 20.1) ml before smoking and 46.4 (SD, 22.7) ml after smoking; this difference did not achieve statistical significance (p = 0.056). There was no significant change in DLCO or VC in six control subjects tested before and after 1 h of sham smoking of an unlit cigarette. In 12 control subjects studied before and after inhalation of 0.1% CO to result in mean COHb levels of 10.6% (SD, 1.4%), there was a slight but significant decrease in VC (mean change, 21%) and in DLCO (mean change, 4%) after correction for COHb back pressure and reduction in available hemoglobin, suggesting that CO inhalation may have a direct effect on DLCO by reducing VC.(ABSTRACT TRUNCATED AT 250 WORDS)