E-cigarettes are battery-powered electronic nicotine delivery device (ENDD) resembling a cigarette designed for the purpose of providing inhaled doses of nicotine by way of a vaporized solution to the respiratory system. These devices provide a flavor and physical sensation similar to that of inhaled tobacco smoke, while no smoke or combustion is actually involved in its operation. For the purpose of the current study, E-cigarettes can be distinct in first generation (A) and second generation devices (B). First-generation devices, generally mimic the size and look of conventional cigarettes and consist of small lithium batteries and cartomizers (i.e. cartridges, which are usually prefilled with a liquid that bathes the atomizer); their batteries may be disposable (to be used once only) or rechargeable. Second-generation devices, consist mainly of higher-capacity (larger) rechargeable lithium batteries and atomizers with the ability to refill them with liquid (sold in separate vials). In the most recent atomizers you can simply change the atomizer head (resistance and wick) while keeping the body of the atomizer, thus reducing the operating costs. They do not resemble conventional cigarettes.