Section IV 
despite such compensatory changes in smoking behavior, 
their intake of the three major smoke components was still lower 
to a statistically and clinically significant degree (Russell et al., 
1986, p. 83). 
Maron and Fortmann (1987) examined the relationship of FTC 
machine-estimated nicotine yield by cigarette brand with the level of 
cigarette consumption and two biochemical measures of smoke exposure 
(expired-air CO and plasma thiocyanate) in a population of 713 smokers. 
These investigators found that the lower the nicotine yield, the greater 
the number of cigarettes smoked per day. Smokers of ultralow-nicotine 
cigarettes experienced smoke exposures that were not significantly different 
from those of smokers of higher yield brands. Only after adjustment for 
number of cigarettes smoked daily did nicotine yield become significantly 
related to expired-air CO and plasma thiocyanate. The number of cigarettes 
smoked per day accounted for 28 and 22 percent of the variance in observed 
expired-air CO and plasma thiocyanate levels, respectively, whereas nicotine 
yield accounted for only 1 and 2 percent of the variance, respectively. The 
authors concluded that machine estimates suggesting low nicotine yield 
underrepresent actual human consumption of harmful cigarette constituents. 
In a study of 289 smokers of cigarettes in the 1-mg FTC tar class, Gori 
and Lynch (1983) observed that nicotine intake (measured by plasma 
cotinine) varied widely, from undetectable to about 800 ng/mL. The 
findings indicated that smokers of low-yield brands tend to take in more 
nicotine than posted FTC values. This observation is illustrated in Figure 3. 
Brand A was .9 tar and .18 nicotine, whereas brand B was .5 tar and 
.10 nicotine. 
Coultas and colleagues (1993), working with a population of 298 mostly 
Hispanic smokers, studied the relationship between yields of cigarettes 
currently smoked and levels of salivary cotinine and expired-air CO. 
Spearman's correlation coefficients (Snedecor and Cochran, 1980) between 
the current number of cigarettes smoked and cotinine or CO were higher 
than correlations between the FTC nicotine data and these same markers. 
In multiple linear regression models, the current number of cigarettes 
smoked was the most important predictor of cotinine and CO levels 
(p < 0.0001), and the addition of FTC tar, nicotine, and CO to the models 
explained little about the variability in cotinine and CO levels. 
In a large-scale study of 2,455 cigarette smokers who smoked their usual 
brands, Wald and colleagues (1984) observed that nicotine and CO intake 
was relatively constant across brands, regardless of stated yield, although tar 
intake appeared related to tar yield. 
YIELD BY THE FTC TEST As pointed out by many researchers, cigarette 
METHOD AND ABSORPTION smoking has the hallmarks of drug-dependent 
OF NICOTINE IN SWITCHERS behavior, with strong evidence that nicotine is 
the dependence-producing component (Benowitz et al., 1989). Nicotine is 
rapidly absorbed into the blood and quickly delivered to the brain, where 
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