Humidification of respiratory gases

Abstract

A humidifier for a respiratory apparatus for delivering a humidified flow of breathable gas to a patient includes a first heating element and a tub configured to store a supply of water to humidify the flow of breathable gas. The tub includes a heat conducting base configured to thermally engage with the first heating element to heat the supply of water in use. The humidifier further includes at least one temperature sensor configured to detect a temperature associated with the first heating element. The humidifier also includes a controller configured to receive signals from the at least one temperature sensor and control the first heating element according to a first heating element duty ratio based on the temperature associated with the first heating element.

1 - 20 . (canceled) 
     
     
         21 . A humidifier for a respiratory apparatus for delivering a humidified flow of breathable gas to a patient, the humidifier comprising:
 a first heating element;   a tub configured to store a supply of water to humidify the flow of breathable gas, the tub including a heat conducting base configured to thermally engage with the first heating element to heat the supply of water in use;   at least one temperature sensor configured to detect a temperature associated with the first heating element; and   a controller configured to receive signals from the at least one temperature sensor and control the first heating element according to a first heating element duty ratio based on the temperature associated with the first heating element,   wherein the controller is configured to adjust the first heating element duty ratio so that:   the first heating element duty ratio has a first value when the temperature associated with the first heating element is below a first threshold,   the first heating element duty ratio has a second value when the temperature associated with the first heating element is above the first threshold and below a second threshold, and   turn the first heating element off when the temperature associated with the first heating element is above the second threshold.   
     
     
         22 . A humidifier according to  claim 21 , wherein the controller is configured to initially heat the water in the tub at an increased rate by setting the first heating element duty ratio at the first value. 
     
     
         23 . A humidifier according to  claim 21 , wherein the first value is higher than the second value. 
     
     
         24 . A humidifier according to  claim 21 , wherein the first value is 100%. 
     
     
         25 . A humidifier according to  claim 21 , wherein the second value is determined based on an evaporation rate required to provide a predetermined absolute humidity, temperature and/or relative humidity to the flow breathable gas. 
     
     
         26 . A humidifier according to  claim 25 , wherein the evaporation rate is a function of a flow rate of the breathable gas. 
     
     
         27 . A humidifier according to  claim 21 , further comprising a flow rate sensor configured to detect a flow rate of the breathable gas. 
     
     
         28 . The humidifier according to  claim 21 , wherein the humidifier is adapted to receive a range of tubs having heat conducting base plates made from different materials. 
     
     
         29 . The humidifier according to  claim 28 , wherein the heat conducting base plates are made from stainless steel, or aluminium. 
     
     
         30 . The humidifier according to  claim 29 , wherein the range of tubs includes a disposable tub and a reusable tub. 
     
     
         31 . A humidifier according to  claim 21 , further comprising an absolute humidity sensor. 
     
     
         32 . A humidifier according to  claim 21 , further comprising a relative humidity sensor. 
     
     
         33 . A respiratory apparatus for providing a humidified flow of breathable gas to a patient, comprising:
 a flow generator to supply the flow of breathable gas;   a humidifier according to  claim 21 , the humidifier being configured to humidify the flow of breathable gas;   a patient interface configured to communicate with the patient's airways; and   an air delivery hose configured to deliver the supply of humidified breathable gas to the patient interface.   
     
     
         34 . A respiratory apparatus according to  claim 33 , wherein the air delivery hose includes a first end configured for connection to an outlet of the humidifier, a second end configured for connection to the patient interface, and a second heating element configured to heat the humidified flow in the air delivery hose. 
     
     
         35 . A respiratory apparatus according to  claim 34 , further comprising humidified flow temperature sensor at the second end of the air delivery hose configured to detect a temperature of the humidified flow at the second end of the air delivery hose and generate signals indicative of the detected temperature of the humidified flow. 
     
     
         36 . A respiratory apparatus according to  claim 35 , wherein the controller is configured to control the second heating element in response to the signals from the humidified flow temperature sensor to provide the humidified flow at the second end of the delivery hose at a predetermined temperature and predetermined relative humidity. 
     
     
         37 . A respiratory apparatus according to  claim 21 , wherein the controller is configured to control the second heating element according to a second heating element duty ratio. 
     
     
         38 . A respiratory apparatus according to  claim 37 , wherein a combined duty ratio is the sum of the first heating element duty ratio and the second heating element duty ratio, and wherein the controller is configured to ensure the combined duty does not exceed 100%. 
     
     
         39 . A respiratory apparatus according to  claim 38 , wherein controller is configured to synchronize the timings of the second heating element duty ratio and the first heating element duty ratio to ensure that the second heating element duty ratio and the first heating element duty ratio do not overlap. 
     
     
         40 . A respiratory apparatus according to  claim 39 , wherein the first heating element duty ratio and the second heating element duty ratio are calculated according to the formula duty ratio=Pf*Td+If*sumTd, wherein Pf is a proportional factor, Td is a difference between the currently sensed temperature and a previous temperature reading, If is an integral factor, and sumTd is a sum of calculated temperature differences Td. 
     
     
         41 . A respiratory apparatus according to  claim 40 , wherein the controller is configured to reduce one or both of the first heating element duty ratio and the second heating element duty ratio when the sum of the first heating element duty ratio and the second heating element duty ratio exceeds 1.0. 
     
     
         42 . A respiratory apparatus according to  claim 41 , wherein the first and second heating elements are configured to share power loading so that the first and second heating elements are not simultaneously active.