Respiratory gas humidification is a method of artificially conditioning respiratory gas for the patient during therapy, and involves humidification, warming, and occasionally filtration of the gas being delivered. If these three measures are not performed to compensate for the natural conditioning of air by the respiratory system, lung infections and lung tissue damage may occur. This is particularly problematic in high gas-flow therapies such as [mechanical ventilation], in patient populations with highly sensitive respiratory tracts (i.e. asthmatics), or among those requiring ventilation for longer periods of time. The two methods currently available for this purpose are active or passive respiratory gas humidification.