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E-cigarettes: an evidence update <br /> <br />69 <br />Ingebrethsen [102] 55 30 2 to 4 10 Lab-built device <br />McAuley et al [90] 50 30 4 50 SCSM <br />Trehy et al [87] 100 60 2 30 Lab-built device <br />Williams & Talbot <br />[103] <br />N.A. 60 2.2 10/11 Lab-built device <br />Cobb et al[86] 35 60 2 ≥50 Machine ISO <br />Trtchounian et al <br />[104] <br />N.A. 60 2.2 10 Lab-built Puff <br />box <br />Uchiyama et al [105] N.A. N.A. N.A. N.A. Premium <br />Smoker <br />Westenberger [85] 100 60 N.A. N.A. Lab-built device <br />Laugesen [106] 38, 58 N.A. N.A. N.A. Syringe <br />N.A., not available. <br /> <br />For instance, the average puff duration in experienced vapers is 2.8 seconds [101], but <br />some studies used puffs lasting for up to 4 seconds. This can overheat the e-liquid and <br />provide unrealistically high readings (see Chapter 11). <br /> <br />Although it would be feasible to establish some empirical standards, eg of puff duration <br />and frequency, by observing vapers, any general standard would have to average <br />values across different products. As different products, and especially products from <br />different ‘generations’, are used differently, such a blanket regimen would still provide <br />inaccurate and potentially misleading information. <br /> <br />A recent study discovered another serious problem with trying to make sense of nicotine <br />content in e-vapour. Across five common e-liquids with middle ranges of strength, the <br />actual nicotine concentration in the e-liquid had almost no relationship with the nicotine <br />content in vapour when the devices were puffed on by a machine at a standard rate <br />[100]. The e-liquid of course had to contain a certain minimal level of nicotine as with <br />little or no nicotine in e-liquid, there would be little or no nicotine in vapour. This finding <br />concerning machine testing also does not mean that nicotine levels in e -liquids are <br />irrelevant for EC users. Although EC technology is developing to maximise nicotine <br />delivery, a vaper seeking high blood nicotine levels is likely to struggle to achieve them <br />with a weak e-liquid. The reason for the low correlation between nicotine in e-liquid and <br />in e-vapour is that the battery output, type of wicks, ventilation holes and other <br />mechanical characteristics of each individual EC product dete rmine how much vapour <br />and nicotine is released – before the individual puffing style and preferences generate <br />yet another key determinant of nicotine delivery to users. <br />