Control of humidifier chamber temperature for accurate humidity control

• US 10,058,663 B2
• Filed: 11/27/2013
• Issued: 08/28/2018
• Est. Priority Date: 05/27/2008
• Status: Active Grant

• Current Assignee: Fisher & Paykel Healthcare Limited
• Original Assignee: Fisher & Paykel Healthcare Limited
• Inventors: Tatkov, Stanislav, Crone, Christopher Malcolm, Hawkins, Peter, Han, Jae Chul, O'Donnell, Kevin Peter, Somervell, Andrew Robert Donald
• Primary Examiner(s): Ditmer, Kathryn E
• Application Number:
  US14/092,488
• Publication Number:
  US 20140166005A1
• Time in Patent Office: 1,735 Days
• CPC Class Codes: A61M 16/0012 by Venturi means
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/0465 Tracheostomy tubes; Devices for performing a tracheostomy; Accessories therefor, e.g. masks, filters
• CPC Class Codes: A61M 16/0666 Nasal cannulas or tubing devices for improving normal breathing through the nose A61F5/08; nose filters A62B23/06; outside holding devices A61M25/02
• CPC Class Codes: A61M 16/0841 for sampling
• CPC Class Codes: A61M 16/0875 Connecting tubes
• CPC Class Codes: A61M 16/1075 by influencing the temperature A61M16/1045 takes precedence
• CPC Class Codes: A61M 16/1085 after being humidified or mixed with a beneficial agent
• CPC Class Codes: A61M 16/109 the humidifying liquid or the beneficial agent
• CPC Class Codes: A61M 16/1095 in the connecting tubes
• CPC Class Codes: A61M 16/16 Devices to humidify the respiration air A61M16/1045 takes precedence
• CPC Class Codes: A61M 16/161 with means for measuring the humidity
• CPC Class Codes: A61M 2205/3368 Temperature

Abstract

A breathing assistance system is provided for delivering a stream flow of heated, humidified gases to a user. The system includes 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 passes through the humidifier and exits via an exit port. The system further includes 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 includes a controller which receives data from the temperature and flow sensors, and which determines a control output in response. The control output is configured to adjust the power to the humidifier unit to achieve a desired output at the humidifier unit exit port.

Claims

1. A breathing assistance system for delivering a flow of gases to a patient for therapeutic purposes, comprising:

a humidifier unit comprising an inlet port and an exit port, said humidifier unit configured to hold and heat a volume of water, said humidifier unit further configured to permit a flow of gases to enter said humidifier unit via said inlet port, pass through said humidifier unit and become heated and humidified, and exit said humidifier unit via said exit port,

an ambient temperature sensor configured to measure a temperature of said flow of gases before said flow of gases enters said humidifier unit,

a conduit configured to deliver said flow of gases from said exit port to said patient via an interface, said conduit comprising a heater wire configured to heat said flow of gases within said conduit,

a patient end temperature sensor configured to measure a temperature of said flow of gases close to said patient,

a flow probe configured to measure a flow rate of said flow of gases through said breathing assistance system, and

a controller configured to;

receive data relating to said temperature of said flow of gases measured by said patient end temperature sensor, data relating to said flow rate measured by said flow probe, and data relating to said temperature measured by said ambient temperature sensor,

determine a target patient end gases temperature based at least in part on said data relating to said flow rate measured by said flow probe and said data relating to said temperature measured by said ambient temperature sensor, wherein said target patient end gases temperature varies based on a change in at least one of said flow rate measured by said flow probe or said temperature measured by said ambient temperature sensor,

compare said target patient end gases temperature to said temperature of said flow of gases measured by said patient end temperature sensor and determine, based on said comparison, a control output comprising a target heater wire power, and

adjust power delivered to said heater wire to substantially match said heater wire power and to cause said temperature of said flow of gases measured by said patient end temperature sensor to substantially match said target patient end gases temperature,

the controller further configured to;

assess that said humidifier unit is experiencing high convective heat loss when said power delivered to said heater wire meets or exceeds a first preset threshold power level for a first preset time period, and adjust power delivered to said heater wire in response to a determination that said humidifier unit is experiencing high convective heat loss.

2. A breathing assistance system as claimed in claim 1, wherein said controller is configured to determine said control output further based at least in part on a rule-based system loaded in a memory of said controller.

3. A breathing assistance system as claimed in claim 1, wherein said controller is configured to determine said control output further based at least in part on at least one mathematical formula loaded in a memory of said controller.

4. A breathing assistance system as claimed in claim 1, wherein said controller is configured to determine said control output using further based at least in part on a look-up table loaded in a memory of said controller.

5. A breathing assistance system as claimed in claim 1, wherein said controller is further configured to adjust power delivered to at least said heater wire to achieve a user-set target dew point temperature.

6. A 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. A breathing assistance system as claimed in claim 1, wherein said ambient temperature sensor is located at or close to said inlet port and is configured to measure the temperature of said flow of gases substantially as it enters said humidifier unit.

8. A breathing assistance system as claimed in claim 1, further comprising an exit port temperature sensor configured to measure a temperature of said flow of gases substantially as it exits said humidifier unit, said controller further configured to receive data relating to said temperature measured by said exit port temperature sensor and to determine said control output further based at least in part on said data relating to said temperature measured by said exit port temperature sensor.

9. A breathing assistance system as claimed in claim 1, wherein said breathing assistance system further comprises a humidity sensor configured to measure humidity of atmospheric gases entering said breathing assistance system, said controller further configured to receive data relating to the measured humidity and determine said control output further based on said data relating to the measured humidity.

10. A breathing assistance system as claimed in claim 1, further comprising a pressure sensor configured to measure a pressure of atmospheric gases entering said breathing assistance system, said controller further configured to receive data relating to said pressure measured by said pressure sensor and to determine said control output further based at least in part on said data relating to said pressure measured by said pressure sensor.

11. A breathing assistance system as claimed in claim 1, further comprising a control unit located in a gases flow path between a central gases source and said humidifier unit, said control unit configured to receive said flow of gases and to deliver said flow of gases to said humidifier unit, said control unit comprising user controls configured to enable a user to set a desired user-set flow rate.

12. A breathing assistance system as claimed in claim 11, further comprising a venturi configured to mix said flow of gases with atmospheric gases before delivering said flow of gases to said humidifier unit.

13. A breathing assistance system as claimed in claim 1, further comprising a blower unit configured to be fluidically connected to said humidifier unit, said blower unit comprising an adjustable, variable speed fan unit configured to deliver said flow of gases over a range of flow rates to said humidifier unit, said blower unit further comprising user controls configured to enable a user to set a user-set flow rate, wherein said controller is further configured to adjust power delivered to at least said blower unit to produce said user-set flow rate.

14. A breathing assistance system as claimed in claim 1, wherein said first preset threshold power level and said first preset time period are stored in a memory of said controller.

15. A breathing assistance system as claimed in claim 1, wherein said humidifier unit further comprises:

a humidifier chamber configured to hold said volume of water,

a heater plate configured to heat said volume of water, and

a heater plate temperature sensor configured to measure a temperature of said heater plate,

wherein said controller is further configured to;

receive data relating to said temperature measured by said heater plate temperature sensor and to adjust power delivered to at least said heater plate.

16. A breathing assistance system as claimed in claim 15, wherein said controller is further configured to:

assess that said humidifier unit is experiencing high convective heat loss when said temperature measured by said heater plate temperature sensor meets or exceeds a second preset threshold temperature for a second preset time period, said second preset threshold temperature and said second preset time period being stored in the memory of said controller, and adjust power delivered to at least said heater plate in response to a determination that said humidifier unit is experiencing high convective heat loss.

17. A breathing assistance system as claimed in claim 1, further comprising an unheated secondary hose configured to fluidically connect a patient end of said conduit comprising said heater wire to said interface, wherein said patient end temperature sensor is located at or close to said patient end of the conduit comprising said heater wire.

18. A breathing assistance system as claimed in claim 1, wherein said controller is further configured to adjust the power delivered to said heater wire to maintain or alter said temperature of said flow of gases to achieve a desired patient end temperature and absolute humidity at said interface.

19. A breathing assistance system as claimed in claim 18, wherein said desired humidity is associated with a user-set target dew point temperature in the range 31-38°

C.

20. A breathing assistance system as claimed in claim 1, wherein said adjustment in response to said determination that said humidifier unit is experiencing high convective heat loss comprises application of an inversely linear correction factor to said power delivered to said heater wire.

21. A breathing assistance system as claimed in claim 1, wherein said controller is configured to determine said target patient end gases temperature further based on pressure of said flow of gases before said flow of gases enters said humidifier unit.