Electronic cigarettes advertised as tobacco-free nicotine delivery systems need more suction than conventional brands, which can affect human health adversely.
The researchers used a smoking machine to compare the smoking properties of eight conventional cigarettes with five e-cigarette brands.
They examined the vacuum required to produce smoke (in the case of conventional cigarettes) or aerosol (in the case of e-cigarettes), and compared the density of the smoke/aerosol over time.
It was found that except for one brand (Liberty Stix), higher vacuums were required to smoke e-cigarettes than conventional brands.
The researchers also found that in the case of e-cigarettes, the aerosol density dropped after the first ten puffs, requiring still stronger suction thereafter to produce aerosol.
"It is too early to know exactly what effect stronger inhaling and diminishing amounts of aerosol will have on human health, but these factors are likely to lead to compensatory smoking, as has been seen previously with 'light' tobacco cigarettes," said Prue Talbot, a professor of cell biology and the senior author of the research paper.
"Our work shows that aerosol density decreases as e-cigarettes are used, requiring stronger puffs over time to sustain density. Manufacturers often claim that e-cigarettes cartridges are equivalent to a certain number of conventional cigarettes. However, this information seems misleading," said Talbot.
Talbot's lab found that while the first ten puffs of an e-cigarette are similar to a conventional cigarette, later puffs were highly variable in aerosol density and do not duplicate smoking of conventional brands.
The researchers found that even though one e-cigarette cartridge may smoke for 200 puffs, cartridges do not smoke uniformly for those 200 puffs and therefore do not duplicate nicotine delivery of individual conventional cigarettes.
"Our results show that e-cigarettes smoke very differently than conventional brands. In preliminary trials, we observed that some brands of e-cigarettes were difficult to smoke possibly because they have relatively small air intake holes. Moreover, the interior of e-cigarettes is dense compared to the relatively porous tobacco-containing cigarettes," said Talbot.
"Based on the results of this paper, not only do users become more aware of the vapor characteristics and smoking properties of e-cigarettes but also manufacturers of e-cigarettes will take notice of the functional inconsistencies of their products," he said.
The results of the study appeared in Nicotine and Tobacco Research.