Effects of freebase/protonated nicotine concentration, liquid composition and electrical power on throat hit in direct-to-lung vaping: theory and clinical measurements

Background For decades, the tobacco industry has engineered the sensory characteristics of combustible tobacco products including the degree of harshness experienced at the back of the throat. Commonly referred to as ‘throat hit’, this harshness derives from absorption of gas phase nicotine and other constituents by the sensory nerves. People who use tobacco products associate throat hit with the positive psychological effects of nicotine, making it a secondary reinforcer for smoking. On the other hand, high throat hit can make products aversive to naïve nicotine users and serves as a barrier to consumption of tobacco products. Methods We developed a first-principles theoretical model to predict nicotine absorption in the throat as a function of electronic nicotine delivery systems (ENDS) device power, liquid composition and puffing topography. The predicted nicotine absorption was compared with subjective throat harshness reported by human participants. We also simulated several ENDS use scenarios to identify the most important processes and factors that govern nicotine absorption in the throat. Results Across various ENDS configurations, we found that computed nicotine gas absorption in the throat was associated with subjective harshness scores (r=0.62; p<0.00001). We also found that liquid nicotine concentration, nicotine form, aerosol temperature and inhalation rate strongly influence nicotine absorption in the throat per unit of nicotine emitted by an ENDS. Conclusions Nicotine throat hit can be predicted and manipulated through ENDS device and liquid design variables. Regulating ENDS throat hit is feasible and may help reduce product appeal to nicotine-naïve individuals while maintaining acceptability for smokers.