Mouth Level Exposure and Similarity to Machine-smoked Constituent Yields.

Standard machine-smoking methods are currently the primary means of determining mainstream cigarette smoke constituent yields for reporting and regulation purposes. Although the International Organization for Standardization (ISO)1 smoking regimen and Cambridge Pad Method (CPM; previously referred to as the Federal Trade Commission method) were originally developed as arbitrary standards to provide comparative information on products’ tar and nicotine yields in mainstream smoke,2 they have been used to estimate smokers’ exposures. However, these smoking regimens have been shown to underestimate actual human exposure to smoke constituents.3 The ISO regimen is nearly identical to CPM; therefore, discussion of the ISO regimen also applies to CPM. The ISO regimen, which does not block any cigarette ventilation holes, allows air to be drawn into the cigarette during a puff, resulting in dilution of smoke constituents. However, as a result of smoke dilution, smokers of highly ventilated cigarettes typically alter their smoking behavior to increase smoke intake by taking larger, deeper puffs, and by blocking ventilation holes with their fingers and/or mouths.4 These behaviors result in higher smoke yields than those estimated by ISO. Thus, levels measured using these regimens do not reflect true smoking behaviors. The Massachusetts Department of Public Health (MDPH)5 and Canadian Intense (CI)6 smoking regimens increase the puff volume and decrease the interpuff interval compared to ISO, and require blocking of either 50% or 100% of the ventilation holes, respectively. These regimens were adopted to supplement ISO yields and provide additional information about cigarette smoke yields when cigarettes are smoked more intensely. However, because individual smokers exhibit a wide range of smoking intensities and puffing behaviors, individual exposure to mainstream smoke constituents varies considerably among smokers and cigarette varieties.7,8 Thus, these regimens by themselves are not more representative of human smoking behavior than ISO and do not provide better predictors of human exposure to smoke constituents.3,9 Furthermore, when using the MDPH regimen, because 50% of the ventilation holes are physically blocked (eg, with tape), there is room for error and variability when utilizing this method. Smoking machine parameters for the ISO, MDPH, and CI regimens are shown in Table 1. Table 1 Puff Parameters for 3 Machine Smoking Methods Additional methods for determining smokers’ exposure to cigarette smoke constituents include analysis of biomarkers of exposure (eg, nicotine, tobacco specific nitrosamines),3,10 machine smoking settings based on actual human puff topography parameters,3 and estimates of smokers’ mouth level exposure (MLE) yields from chemical analysis of the filters of spent cigarette butts.11 A variety of chemicals can be assessed using filter analysis, including tar (total particulate matter), nicotine, solanesol, and other chemicals.11–14 MLE yields can provide indirect estimates of nicotine and tar yields achieved by individual smokers of individual cigarettes; filter analysis has been shown to correlate well with salivary cotinine and urinary nicotine metabolite levels.10,15 Filters from cigarette butts are collected from smokers smoking their regular brand in their natural environment as opposed to human puffing behavior recorded using machinery in a laboratory or clinical setting. Thus, MLE yields can account for differences in smoking behaviors and patterns, and provide more accurate estimates of human smoked cigarette constituent yields than smoking machine regimens.11 The goal of this report was to examine peer-reviewed literature to determine the smoking regimen that may be used for tobacco product regulation based on the fraction of cigarette smoke yields that best estimate the range of human smoke exposures. Whereas previous reports have typically compared machine smoking regimen yields to human smoking topography,3,16 the current review compares studies of machine smoking regimen yields to human MLE yields. Studies reporting the percentage of smokers who smoke more or less like a particular smoking regimen, based on MLE data, were examined.