Smoking and the use of lower tar yield cigarettes.

The aim of this thesis was to investigate smoking behaviour in a population of habitual cigarette smokers. Measurements were made 5 times, at intervals of 4 weeks whilst smoking cigarettes with tar yields above 10 mg. After switching to lower yield cigarettes (reductions of at least 3 mg tar and 0.2 mg nicotine) a further 6 visits were made at intervals of 6 weeks. A group of subjects followed the same protocol but without switching. Tobacco smoke uptake was estimated by measuring pre and post-smoking plasma nicotine, cotinine, carboxyhaemoglobin (HbCO) and expired carbon monoxide (infinity). Smoke generation was measured with the subject smoking through a holder acting as a flow meter. The data from visits 2-6 showed large between-subject variability but little between-session variability indicating that these measures were reproducible. However, the large variation in measurements of plasma nicotine may limit the use of this variable unless sample collection is carefully controlled. There were observed gender differences in smoke generation which could be explained in terms of anatomical size. Examination of the interrelationships between measurements of smoking showed that although some indices were highly correlated, much of the variation in the relationship could not be explained Indicating that no one measurement can give an overall indication of smoke exposure. 497 people expressed an interest in the study but only 53 managed to complete. Of these 44 met the study criteria: 26 switched to a lower yield brand and 18 remained on their own brand. The switching group showed significant increases in puff volume, peak puff flow, puff number and total puff volume, whilst pre-smoke Hbinfinity, the HbCO boost, mean plasma cotinine and puff interval showed significant reductions. These changes resulted in an average level of regulation of about 56%. The majority of these changes were maintained over the post-switch period, however, puff number, puff interval and total puff volume showed short-term adaptation by returning to baseline values after an initial change. It is concluded that the effects of switching to lower yield cigarettes persist for at least 8 months (average level of regulation of about 65%) and that this has Important implications for the strategy of reducing cigarette smoke exposure. It was postulated that smoking results in transient changes in pulmonary ventilation/perfusion (VA/Q) and this mechanism may explain the discrepancy between the relative boost for the non-lnvasive and Invasive methods of measuring changes in HbCO on smoking. Both breath-hold and mean alveolar methods were significantly affected by posture Induced changes in VA/Q Indicating that equilibration between CX) in blood and the lungs cannot be assumed for these methods. However, these techniques do provide a reasonable estimate of Hb? before smoking as long as the same method and conditions are adhered to. Although unaffected by changes in posture, the rebreathing method also failed to reflect changes in Hb? on smoking since the relative infinity boost was only half that for Hbinfinity. It is therefore concluded that none of the alveolar sampling techniques give a reliable indication of the acute changes In Hbinfinity associated with smoking