Exposure to carbon monoxide in smokers of middle- and low-tar cigarettes.

The carbon monoxide (CO) exposure of habitual middle-tar (MT) and low-tar (LT) smokers was studied in a group of 78 subjects (38 male and 40 female). CO intake from a single cigarette (measured by the rise in expired-air CO concentration) was significantly less in LT smokers. Longer term exposure, measured by pre-smoking CO levels, was also less in LT smokers, but not significantly so. A CO-based index showed that LT cigarettes were relatively more intensively smoked. Exposure to nicotine and tar was estimated by applying the index of smoking intensity to the standard nicotine and tar yields of the brands smoked. Although an indirect estimate, the results suggest that the intake of tar and nicotine is likely to be appreciably less in LT smokers than in their MT counterparts. The likely difference in intake, however, is not as great as the difference in smoking-machine yields.