Reconciling human smoking behavior and machine smoking patterns: implications for understanding smoking behavior and the impact on laboratory studies

Abstract

Background: Recent Food and Drug Administration legislation enables the mandating of product performance standards for cigarette smoke and the evaluation of manufacturers' health claims for modified tobacco products. Laboratory studies used for these evaluations and also for understanding tobacco smoke toxicology use machines to generate smoke. The goal of this review is to critically evaluate methods to assess human smoking behavior and replicate this in the laboratory.

Methods: Smoking behavior and smoking machine studies were identified using PubMed and publicly available databases for internal tobacco company documents.

Results: The smoking machine was developed to generate smoke to allow for comparing cigarette tar and nicotine yields. The intent was to infer relative human disease risk, but this concept was flawed because humans tailor their smoking to the product, and chemical yields and toxicologic effects change with different smoking profiles. Although smoking machines also allow for mechanistic assessments of smoking-related diseases, the interpretations also are limited. However, available methods to assess how humans puff could be used to provide better laboratory assessments, but these need to be validated. Separately, the contribution of smoke mouth-holding and inhalation to dose need to be assessed, because these parts of smoking are not captured by the smoking machine. Better comparisons of cigarettes might be done by tailoring human puff profiles to the product based on human studies and comparing results across regimens.

Conclusions: There are major research gaps that limit the use of smoking machine studies for informing tobacco control regulation and mechanistic studies.

Figures

Figure 1. Schematic Representation of the Puff and Inhalation/Exhalation Pattern

Reproduced from a British American Tobacco Company document, simultaneous measurements were assessed for inhalation/exhalation and smoking topography. The following parameters are defined from this figure: puff volume (ml) - integration of puff pressure curve from A to C; lit draw resistance (cm H2O/ml) - the ration of integrated pressure to puff volume; puff duration - time from A to C; inhalation delay time (sec) - the time from completion of the puff to the start of inhalation from C to E; inspiratory time (sec) - the duration of time from E to F; breath hold time (sec) - the delay from the end of active inhalation to start of exhalation from F to G; expiratory time (sec) - the time for exhalation from G to H; inhalation volume (ml) - the volume difference from E1 to F1; exhalation volume (ml) - the volume difference from G1 to H1; volume change prior to inhalation (ml) - volume shift in the lungs (usually exhalation) that occurs during the puff and inhalation delay period from D to E1; volume change after puff (ml) - volume change after the puff but before the inhalation, from C1 to E1.

Figure 2. Puffing and inhalation patterns showing interindividual variation during the interval between puffing and inhalation

Puffing begins during exhalation from points A to B. For some smokers, the smoke is immediately inhaled from the mouth into the pharynx and lungs and completed at point C (A); for others, there is a mouth holding period where point C marks the beginning of the inhalation and completed at D (B); for others, there is an immediate inhalation until point C then an exhalation followed by an larger inhalation at point D (C); others have an immediate exhalation followed by an inhalation from points C to D (D).