The following letter provides additional information to help us evaluate what the research did and did not establish scientifically.
To the Editors:
The findings by Vardavas and colleagues are not conclusive due to the small number of subjects studied, the choice of study outcomes of unclear clinical relevance, together with the lack of appropriate study controls. [1] The small changes in FeNO and peripheral flow resistance (IOS) reported may be non specific. A possible explanation for the small decrease in FeNO and the trivial increase in peripheral flow resistance (IOS) is that the mist generated by the e-cigarette per se might have contributed to these changes. In a series of pilot studies aimed at optimizing the distribution of several respiratory investigations within a protocol for the detailed characterization of the asthma phenotype (U-BIOPRED), researchers discovered that nebulization of saline can reduce FeNO up to 25% from baseline (personal observation). For this reason baseline assessment of induced sputum has to follow measurement of FeNO. Therefore, authors should have included a different control (e.g. saline mist generated by a ultrasonic nebulizer) for their study. Also, another reasonable comparator that should have been used as control was participants’ own brand cigarette.
In the Summary, the authors state that the e-cigarettes tested in their study "have immediate adverse physiologic effects after short term use that are similar to some of the effects seen with tobacco smoking". The reported 16% decrease in FeNO (i.e. 2.1 ppb in absolute term!) and 11% increase in peripheral flow resistance (IOS) (i.e. 0.025 kPa/L/s in absolute term!) after e-cigarette use from baseline are so small and well within tests variability [2,3] that it is highly unlikely to have meaningful adverse effects.
Of note, no changes were detected by canonical pulmonary function testing after e-cigarette use. Detailed toxicology characterization of the components contained in the e-cigarettes tested in the study demonstrates that their primary components (i.e. water, propylene glycol, and nicotine) are not harmful, and this is in agreement with the detailed analysis of e-cigarette toxicology by Cahn and Siegel [4]. Moreover, a recent clinical safety assessment of one such product in 40 smokers showed that mouth and throat irritation and dry cough were commonly reported in the initial few weeks of use, but all appeared to wane spontaneously by the end of the study, after 24 weeks of regular use [5]. Thus the authors’ conclusions are not fully supported by the data, and the accumulating evidence is rather strongly supportive of a good safety profile for the e-cigarettes.
References
1. Vardavas CI, Anagnostopoulos N, Kougias M, Evangelopoulou V, Connolly GN, Behrakis PK. Acute pulmonary effects of using an e-cigarette: impact on respiratory flow resistance, impedance and exhaled nitric oxide. Chest. 2011 Dec 22. [Epub ahead of print].
2. Oostveen E, MacLeod D, Lorino H, et al. The forced oscillation technique in clinical practice: methodology, recommendations and future developments. Eur Respir J 2003; 22:1026-1041.
3. Dweik RA, Boggs PB, Erzurum SC, Irvin CG, Leigh MW, Lundberg JO, Olin AC, Plummer AL, Taylor DR; American Thoracic Society Committee on Interpretation of Exhaled Nitric Oxide Levels (FENO) for Clinical Applications. An official ATS clinical practice guideline: interpretation of exhaled nitric oxide levels (FENO)
for clinical applications. Am J Respir Crit Care Med. 2011;184(5):602-15.
4. Cahn Z, Siegel M. Electronic cigarettes as a harm reduction strategy for tobacco control: A step forward or a repeat of past mistakes? J Public Health Policy. 2011;32(1):16-31.
5. Polosa R, Caponnetto P, Morjaria JB, Papale G, Campagna D, Russo C. Effect of an electronic nicotine delivery device (e-Cigarette) on smoking reduction and cessation: a prospective 6-month pilot study. BMC Public Health. 2011;11:786.
