Self-selected blocking of vents on low-yield cigarettes

levels of carbon monoxide (CO) and salivary cotinine than did nonblockers. None of the blockers reported that they blocked vents. Exposure differences seemed not to be due simply to vent blocking, but also to be the result of syndromes ofheavier (blocking, more cigarettes per day, and starting earlier in the morning) or lighter smoking (not blocking, fewer cigarettes per day, and starting later in the morning). The results are interpreted inlight of the boundary model. Cigarette smoking and brand selection should be studied as they occur naturally, as well as in experimentally contrived studies. Cigarettes Smoking Tobacco Smoking topography Hole blocking Nicotine dependence Filter ventilation Low-yield cigarettes Boundary model COMMERCIAL ultra-low-yield cigarettes (-<4 mg tar, 0.4 mg nicotine) depend upon ventilated filters to reduce tar and nicotine yields (12). Blockade of filter vents--typically with lips or fingers--is one way in which smokers can compensate for the low yields (15, 17, 18, 20), but it is still unresolved how vent blocking contributes to actual exposures to cigarette smoke in the natural environment. In the laboratory, complete blockade of cigarettes yielding