Patent ID: 7962018

Claim:
A breathing assistance apparatus adapted to deliver humidified gases at a desired level of humidity or at a desired temperature to a patient, comprising: a humidifier including a heater, a heater temperature sensor providing an indication of the heater temperature, and a heater power input for energising said heater, said humidifier adapted to receive a chamber for holding a volume of water, said heater adapted to transfer heat to water within said chamber to produce water vapour within said chamber, said gases in use passing through water vapour within said chamber thereby being humidified; and a controller adapted to monitor and control said heater power input so as to energise said heater to humidify said gases to said desired level of humidity or said desired temperature, said controller configured to: energise said heater to a level of heater power required to maintain the heater temperature at a predetermined initial heater temperature; based on said level of heater power required to maintain the heater temperature at said predetermined initial heater temperature, determine a heater temperature set-point required to humidify said gases to said desired level of humidity or said desired temperature; energise said heater to substantially maintain the heater temperature at said heater temperature set-point; and without the necessity of receiving information from additional sensors beyond the heater temperature sensor, continuously monitor said heater power input and based on the heater power required to substantially maintain the heater temperature at said heater temperature set-point, re-determine said heater temperature set-point required to humidify said gases to said desired level of humidity or said desired temperature, wherein: when a change in the heater power is more than a first threshold and less than a second threshold, re-determine said heater temperature set-point required to humidify said gases to said desired level of humidity or said desired temperature; and when a change in the heater power is more than said second threshold, energise said heater to the level of heater power required to maintain the heater temperature at the predetermined initial heater temperature, wherein said second threshold is higher than said first threshold.