Humidity controller

Abstract

A breathing assistance apparatus adapted to deliver humidified gases at a desired level of humidity to a patient including a humidifier and a heated conduit is disclosed. The humidifier includes a controller which determines the flow rate of the gases and then determines the required power input to the humidifier to deliver the gases to the patient at the required patient humidity. This means the need for external sensors is dispensed with and thus the apparatus is simple and less bulky.

1 - 32 . (canceled) 
     
     
         33 . A breathing assistance apparatus comprising:
 a heater configured to heat water to humidify gases, the heater further configured to be in a fluid communication with a conduit configured to deliver the gases to a patient; and   a controller configured to:
 cause an initial power level to be supplied to the heater to maintain a heater temperature at an initial temperature level; 
 determine a flow rate of the gases based on an output of a flow sensor; 
 based on the flow rate of the gases, determine a power level to heat the gases to a selected temperature or humidify the gases to a selected humidity and cause the determined power level to be supplied to the heater; 
 monitor a change in the flow rate of the gasses; 
 in response to determining that the change in the flow rate of the gases satisfies a first threshold but does not satisfy a second threshold, redetermine the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity and cause the redetermined power level to be supplied to the heater; and 
 in response to determining that the change in the flow rate satisfies the second threshold, cause the initial power level to be supplied to the heater, the second threshold being indicative of a larger change in the flow rate of the gases than the first threshold. 
   
     
     
         34 . The apparatus of  claim 33 , wherein the controller is further configured to:
 in response to determining that 1) the change in the flow rate of the gases satisfies the first threshold but does not satisfy the second threshold and 2) the change in the flow rate of the gases indicates an increase in the flow rate of the gases, delay redetermination of the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity for a first period of time.   
     
     
         35 . The apparatus of  claim 34 , wherein the controller is further configured to:
 in response to determining that 1) the change in the flow rate of the gases satisfies the first threshold but does not satisfy the second threshold and 2) the change in the flow rate of the gases indicates a decrease in the flow rate of gases, delay redetermination of the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity for a second period of time shorter than the first period of time.   
     
     
         36 . The apparatus of  claim 33 , further comprising a temperature sensor configured to measure the heater temperature, wherein the controller is further configured to:
 determine an expected heater temperature based on the flow rate of the gasses; and   in response to determining that the expected heater temperature deviates from the measured heater temperature by a threshold temperature, redetermine the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity and cause the redetermined power level to be supplied to the heater.   
     
     
         37 . The apparatus of  claim 33 , wherein the flow rate of the gases depends at least in part on one or more restrictions in a flow path configured to accommodate a flow of the gases. 
     
     
         38 . The apparatus of  claim 33 , wherein the controller is further configured to determine a conduit heater power level to heat the gases flowing through the conduit and cause the conduit heater power level to be supplied to the conduit heater. 
     
     
         39 . The apparatus of  claim 38 , wherein the controller is further configured to increase the conduit heater power level in response to at least one of: increase in the flow rate of the gases, decrease in ambient temperature, or increase in a difference between the ambient temperature and a temperature of the gases. 
     
     
         40 . A breathing assistance apparatus comprising:
 a heater configured to heat water to humidify gases, the heater further configured to be in a fluid communication with a conduit configured to deliver the gases to a patient; and   a controller configured to:
 cause an initial power level to be supplied to the heater to maintain a heater temperature at an initial temperature level; 
 estimate a flow rate of the gases; 
 based on the estimated flow rate of the gases, determine a power level to heat the gases to a selected temperature or humidify the gases to a selected humidity and cause the determined power level to be supplied to the heater; 
 monitor a change in the flow rate of the gasses; 
 in response to determining that the change in the flow rate of the gases satisfies a first threshold but does not satisfy a second threshold, redetermine the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity and cause the redetermined power level to be supplied to the heater; and 
 in response to determining that the change in the flow rate satisfies the second threshold, cause the initial power level to be supplied to the heater, the second threshold being indicative of a larger change in the flow rate of the gases than the first threshold. 
   
     
     
         41 . The apparatus of  claim 40 , further comprising a fan configured to blow the gases through a flow path, wherein the controller is configured to estimate the flow rate of the gases based on loading of the fan. 
     
     
         42 . The apparatus of  claim 41 , wherein the flow rate of the gases depends at least in part on one or more restrictions in the flow path. 
     
     
         43 . The apparatus of  claim 40 , further comprising a temperature sensor configured to measure ambient temperature, wherein the controller is configured to estimate the flow rate of the gases based on the power level to heat the gases to the selected temperature or humidify the gases to the selected humidity and the ambient temperature. 
     
     
         44 . The apparatus of  claim 40 , further comprising a temperature sensor configured to measure the heater temperature, wherein the controller is configured to estimate the flow rate of the gases based on a ratio of the determined power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity and the heater temperature measured by the temperature sensor. 
     
     
         45 . The apparatus of  claim 40 , wherein the controller is further configured to:
 in response to determining that 1) the change in the flow rate of the gases satisfies the first threshold but does not satisfy the second threshold and 2) the change in the flow rate of the gases indicates an increase in the flow rate of the gases, delay redetermination of the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity for a first period of time; and   in response to determining that 1) the change in the flow rate of the gases satisfies the first threshold but does not satisfy the second threshold and 2) the change in the flow rate of the gases indicates a decrease in the flow rate of gases, delay redetermination of the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity for a second period of time shorter than the first period of time.   
     
     
         46 . The apparatus of  claim 40 , further comprising a temperature sensor configured to measure the heater temperature, wherein the controller is further configured to:
 determine an expected heater temperature based on the flow rate of the gasses; and   in response to determining that the expected heater temperature deviates from the measured heater temperature by a threshold temperature, redetermine the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity and cause the redetermined power level to be supplied to the heater.   
     
     
         47 . The apparatus of  claim 40 , wherein the controller is further configured to determine a conduit heater power level to heat the gases flowing through the conduit and cause the conduit heater power level to be supplied to the conduit heater. 
     
     
         48 . The apparatus of  claim 47 , wherein the controller is further configured to increase the conduit heater power level in response to at least one of: increase in the flow rate of the gases, decrease in ambient temperature, or increase in a difference between the ambient temperature and a temperature of the gases. 
     
     
         49 . A method of operating a breathing assistance apparatus, the method comprising, by a controller of the breathing assistance apparatus:
 causing an initial power level to be supplied to a heater of the breathing assistance apparatus to maintain a heater temperature at an initial temperature level, the heater configured to heat water to humidify gases;   estimating a flow rate of the gases;   based on the estimated flow rate of the gases, determining a power level to heat the gases to a selected temperature or humidify the gases to a selected humidity and causing the determined power level to be supplied to the heater;   monitoring a change in the flow rate of the gasses;   in response to determining that the change in the flow rate of the gases satisfies a first threshold but does not satisfy a second threshold, redetermining the power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity and causing the redetermined power level to be supplied to the heater; and   in response to determining that the change in the flow rate satisfies the second threshold, causing the initial power level to be supplied to the heater, the second threshold being indicative of a larger change in the flow rate of the gases than the first threshold.   
     
     
         50 . The method of  claim 49 , wherein estimating the flow rate of the gases comprises determining loading of a fan of the breathing assistance apparatus. 
     
     
         51 . The method of  claim 49 , wherein estimating the flow rate of the gases is based on the power level to heat the gases to the selected temperature or humidify the gases to the selected humidity and ambient temperature. 
     
     
         52 . The method of  claim 49 , wherein estimating the flow rate of the gases comprises determining a ratio of the determined power level to heat the gases to the selected temperature or to humidify the gases to the selected humidity and the heater temperature measured by a temperature sensor of the breathing assistance apparatus. 
     
     
         53 . The method of  claim 49 , wherein estimating the flow rate of the gases comprises determining the flow rate of the gases based on an output of a flow sensor of the breathing assistance apparatus.