1. The present experiment describes an attempt to select differentially nicotine dependent smokers by means of an objective and non-invasive measure of cigarette smoke CO absorption. Toward this goal the differences in expiratory tidal air CO concentration before and after smoking a single cigarette (tidal CO boost) were measured in three experimental sessions. The selection criteria were tidal CO boosts greater than 3.5 p.p.m. and less than 1 p.p.m. According to these criteria 19 out of 171 subjects were consistently found to be high CO absorbers and 20 were found to be low CO absorbers.
2. Puffing behaviour was measured throughout all three test sessions by the flowmeter method and respiratory inhalation by thorax impedance plethysmography. In addition, heart rate was continuously measured during smoking. These data were used to assess for specific differences between the two extremes of inhalation behaviour.
3. High CO absorbers differed from low CO absorbers by more intensive patterns of puffing and respiratory inhalation, by higher daily cigarette and coffee consumption, by lower alcohol consumption, by shorter latencies to the first cigarette in the morning, by greater subjective need for smoking and by lower scores for healthy eating habits. No intergroup differences were observed for smoking induced heart rate acceleration. The high CO absorbers were significantly older than the low CO absorbers; however, no evidence was found that any of the differences in smoking style between the two extremes might be related to their difference in age. No differences were seen in cigarette strengths, in personality or in coronary prone behaviour as assessed by means of standardized questionnaires in all subjects.
4. It is concluded that nicotine plays a more important role in smoking motivation among the high than among the low CO absorbing smokers. The role of nicotine and the individual dosage absorbed by the smokers, however, remain to be analysed further and are discussed in the light of nicotine tolerance effects.