Development of inhalation exposure system for assessing respiratory safety of nicotine-free inhalator as nonignition smoking cessation aid

Abstract

In this study, we aimed to develop and evaluate an inhalation exposure system involving vapor generation for a nonignition smoking cessation aid, a nicotine-free inhalator, with the objective of assessing its respiratory safety by obtaining inhalation safety data. The vapor was generated by blowing air into the raw material of the inhalator, and the vapor concentration was controlled by adjusting the inhalation exposure conditions: the amount of raw material (5, 50, and 100 g), flow rate (0.1, 1, and 2 L min−1), and temperature (25, 40, and 80 °C). We evaluated the effectiveness of the inhalation exposure system by examining the generated concentrations of the main component in the vapor of the nicotine-free inhalator, L-menthol, the concentration of which varied based on inhalation exposure conditions. This concentration of L-menthol proportionally increased with increasing amounts of raw material (slope = 0.4625 mg m−3 g−1 and R2 = 0.9763). The concentration of L-menthol in the vapor increased as the generation flow rate decreased and remained at a relatively consistent level for the 6 h necessary for inhalation toxicity assessment (–79.38 mg m−3 L–1 min and R2 = 0.9262). The L-menthol concentration in the vapor increased by approximately five times when the generation temperature was increased from 25 °C to 80 °C. However, the change in the L-menthol concentration in the vapor after 6 h was substantial, ranging from 20% to 50%. In other words, the generated concentration of vapor is temperature-sensitive, so producing a constant concentration level would be challenging. By adjusting the amount of raw material and generation flow rate of this nicotine-free inhalator, we obtained a vapor sample for the respiratory safety assessment of nonignition smoking cessation aids.