Control of humidifier chamber temperature for accurate humidity control

Abstract

A breathing assistance system for delivering a stream of heated, humidified gases to a user, comprising a humidifier unit which holds and heats a volume of water, and which in use receives a flow of gases from a gases source via an inlet port, the flow of gases passing through the humidifier and exiting via an exit port, the system further having a temperature sensor which measures the temperature of the gases exiting the humidifier unit, an ambient temperature sensor which measures the temperature of gases before they enter the humidifier unit, and a flow sensor which measures the flow rate of the gases stream, the system also having a controller which receives data from the temperature and flow sensors, and which determines a control output in response, the control output adjusting the power to the humidifier unit to achieve a desired output at the humidifier unit exit port.

What is claimed is: 
     
         1 . A breathing assistance system configured to deliver a stream of gases for therapeutic purposes, comprising:
 a humidifier including an inlet port and an exit port, said humidifier configured to receive a flow of gases from a gases source via said inlet port and hold and heat a volume of water, said flow of gases passing through said humidifier, becoming heated and humidified, and exiting said humidifier via said exit port;   a delivery conduit configured to receive said flow of gases from said exit port for delivery to a user via an interface, said delivery conduit including a heater wire configured to heat the flow of gases within said delivery conduit;   a patient end temperature sensor adapted to measure a first temperature relating to said flow of gases at or close to said user;   an exit port temperature sensor configured to measure a second temperature relating to said flow of gases exiting said humidifier;   an ambient temperature sensor adapted to measure a third temperature relating to said flow of gases before said flow of gases enters said humidifier;   a flow sensor configured to measure a flow rate of said flow of gases; and   a controller configured to:
 receive data from said patient end temperature sensor relating to the first temperature, data from said exit port temperature sensor relating to the second temperature, data from said ambient temperature sensor relating to the third temperature, and data from said flow sensor relating to the flow rate, 
 based on said data relating to the second and third temperatures and said data relating to the flow rate, determine a first control output for adjusting power provided to said humidifier to achieve a first desired output at said exit port, and 
 based in said data relating to the first temperature and said data relating to the flow rate, determine a second control output for adjusting power provided to said heater wire to maintain or alter a temperature of said flow of gases within said delivery conduit to achieve a second desired output at said interface. 
   
     
     
         2 . The breathing assistance system as claimed in  claim 1 , wherein said first control output relates to a target temperature at said exit port for a given flow level, said first desired output comprises a target temperature at said exit port, and said first control output adjusts said power provided to said humidifier to match said second temperature with said target temperature at said exit port. 
     
     
         3 . The breathing assistance system as claimed in  claim 1 , wherein said second control output relates to a target temperature at said interface for a given flow level, and said second control output adjusts said power provided to said heater wire to match said first temperature with said target temperature at said interface. 
     
     
         4 . The breathing assistance system as claimed in  claim 1 , wherein the controller is configured to determine at least one of said first control output or second control output based at least in part on a rule-based system loaded in a memory of said controller, a mathematical formula loaded in the memory, or a look-up table loaded in the memory. 
     
     
         5 . The breathing assistance system as claimed in  claim 1 , wherein at least one of said first or second desired output comprises a user-set target dew point temperature. 
     
     
         6 . The breathing assistance system as claimed in  claim 5 , wherein said user-set target dew point temperature relates to an absolute humidity level of substantially 44 mg H2O/liter of air. 
     
     
         7 . The breathing assistance system as claimed in  claim 1 , wherein at least one of a target temperature at said interface or a target temperature at said exit port is in the range of 31-39° C. 
     
     
         8 . The breathing assistance system as claimed in  claim 1 , wherein at least one of said first or second desired output comprises a target absolute humidity. 
     
     
         9 . The breathing assistance system as claimed in  claim 1 , wherein at least one of said first or second desired output comprises a target temperature and relative humidity. 
     
     
         10 . The breathing assistance system as claimed in  claim 1 , further comprising one or more user controls configured to enable said user to set a desired user-set flow rate of gases. 
     
     
         11 . The breathing assistance system as claimed in  claim 10 , further comprising a flow controller configured to receive said flow of gases from a remote central source, said flow controller located between said remote central source and said humidifier, said flow controller receiving said flow of gases and passing said flow of gases on to said humidifier via a gases connection path between said humidifier and said flow controller, said one or more user controls configured to enable said user to set said desired user-set flow rate. 
     
     
         12 . The breathing assistance system as claimed in  claim 11 , wherein said flow controller further comprises a venturi adapted to mix said flow of gases from said remote central source with atmospheric gases before passing said flow of gases to said humidifier. 
     
     
         13 . The breathing assistance system as claimed in  claim 1 , wherein said gases source comprises a blower configured to be fluidically connected to said humidifier, said blower including an adjustable, variable speed fan unit configured to deliver said flow of gases over a range of flow rates to said humidifier and one or more user controls configured to enable said user to set a desired user-set flow rate, said controller configured to control power provided to said blower to produce said desired user-set flow rate. 
     
     
         14 . The breathing assistance system as claimed in  claim 1 , wherein said humidifier comprises a humidifier chamber including a heater base, and said breathing assistance system further comprises:
 a heater plate adapted to heat contents of said humidifier chamber by providing energy to said heater base; and   a heater plate temperature sensor adapted to measure a fourth temperature relating to said heater plate, said controller further configured to determine said first control output by assessing the second, third, and fourth temperatures and said flow rate and adjusting at least power provided to said heater plate to match said second temperature to a target temperature at said exit port.   
     
     
         15 . The breathing assistance system as claimed in  claim 1 , further comprising a humidity sensor configured to measure a humidity of atmospheric gases entering said humidifier, said controller configured to determine at least one of said first control output or said second control output further based on data relating to the measured humidity. 
     
     
         16 . The breathing assistance system as claimed in  claim 1 , wherein the controller is configured to determine said second control output further based on said data related to the third temperature. 
     
     
         17 . A method of operating a breathing assistance system that delivers a stream of gases for therapeutic purposes, the method comprising:
 under control of a controller of the breathing assistance system:
 determining a first temperature relating to a flow of gases at or close to a user, said flow of gases configured to enter a humidifier of the breathing assistance system via an inlet port, become heated and humidified, and exit said humidifier via an exit port, said flow of gases configured to be delivered to a user via an interface, said interface configured to be connected to said humidifier by a delivery conduit including a heater wire configured to heat the flow of gases within said delivery conduit; 
 determining a second temperature relating to said flow of gases exiting said humidifier; 
 determining a third temperature relating to said flow of gases before said flow of gases enters said humidifier; 
 determining a flow rate of said flow of gases; 
 based on the second and third temperatures and the flow rate, determining a first control output for adjusting power provided to said humidifier to achieve a first desired output at said exit port; and 
 based on the first temperature and the flow rate, determining a second control output for adjusting power provided to said heater wire to maintain or alter a temperature of said flow of gases within said delivery conduit to achieve a second desired output at said interface. 
   
     
     
         18 . The method as claimed in  claim 17 , wherein said first control output relates to a target temperature at said exit port for a given flow level, said first desired output comprises a target temperature at said exit port, and said first control output adjusts said power provided to said humidifier to match said second temperature with said target temperature at said exit port. 
     
     
         19 . The method as claimed in  claim 17 , wherein said second control output relates to a target temperature at said interface for a given flow level, and said second control output adjusts said power provided to said heater wire to match said first temperature with said target temperature at said interface. 
     
     
         20 . The method as claimed in  claim 17 , wherein determining at least one of said first control output or second control output is based at least in part on a rule-based system loaded in a memory of said controller, a mathematical formula loaded in the memory, or a look-up table loaded in the memory. 
     
     
         21 . The method as claimed in  claim 17 , wherein at least one of said first or second desired output comprises a target temperature and relative humidity.