Respiratory humidification system

• US 6,802,314 B2
• Filed: 03/13/2002
• Issued: 10/12/2004
• Est. Priority Date: 06/17/1997
• Status: Expired due to Term

• Current Assignee: Fisher & Paykel Healthcare Limited
• Original Assignee: Fisher & Paykel Limited
• Inventors: McPhee, Stephen William
• Primary Examiner(s): Lo, Weilun
• Assistant Examiner(s): WIEKER, AMANDA FLYNN
• Application Number:
  US10/097,675
• Publication Number:
  US 20020139367A1
• Time in Patent Office: 944 Days
• Field of Search: 128/203.12, 128/203.16, 128/203.17, 128/203.26, 128/204.17, 128/204.22, 261/129, 261/130, 261/131, 261/142, 261/DIG.65, 219/490, 219/494, 165/222, 165/223, 165/229, 165/230, 165/253, 165/281, 165/287-290, 165/295, 236/44.M, 236/20.E, 236/912, 236/DIG.13, 392/460-466
• US Class Current: 128/203.17
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0066 Blowers or centrifugal pumps
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/0841 for sampling
• CPC Class Codes: A61M 16/1075 by influencing the temperature A61M16/1045 takes precedence
• 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 16/162 Water-reservoir filling system, e.g. automatic
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2205/18 with alarm
• CPC Class Codes: A61M 2205/3331 Pressure; Flow
• CPC Class Codes: A61M 2205/3368 Temperature
• CPC Class Codes: G01F 1/684 Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6888 Thermoelectric elements, e.g. thermocouples, thermopiles
• CPC Class Codes: G08B 21/16 Combustible gas alarms
• CPC Class Codes: Y10S 261/65 Vaporizers

Abstract

A flow probe for use in a humidification system is disclosed. The flow probe is adapted to be positioned in a humidified gases flow (for example oxygen or anaesthetic gases) such as that which is provided to a patient in a hospital environment. The flow probe is designed to provide both temperature and flow rate sensing of the gases flow by incorporating two sensors (preferably thermistors) and the shape and alignment of the probe enables accurate readings by reducing the occurrence of condensation on the sensors. A number of possible applications are disclosed wherein the flow sensor is included in humidification control systems which provide a patient with a desired humidity level or simplify the amount of user input required or wherein the flow sensor provides a controller with flow information which may then be used to determine certain, possibly dangerous, conditions (such as incorrect flow sensor placement, breathing circuit disconnected, no water in the humidification chamber or humidity out of required limits).

Claims

1. Humidification apparatus for humidifying a gas flow to be supplied to a patient or other person in need of such gas comprising:

humidification chamber means for holding a quantity of water and having an inlet and an outlet to allow said gas flow to pass through said humidification chamber means,

gas flow temperature sensing means for sensing the gas temperature within or adjacent said humidification chamber means,

heating means provided adjacent said humidification chamber means for providing heat to said quantity of water in said humidification chamber means in order to provide water vapour to said gas flow passing through said humidification chamber means,

heating means power utilisation sensing means for monitoring power being used by said heating means,

temperature sensing means for sensing the temperature of said heating means,

gas transportation pathway means connected to said outlet of said humidification chamber means for conveying said gas flow to said patient or other person in need of such gas, said gas transportation pathway means having a patient end, distal to said end connected to said outlet of said humidification chamber means,

alarm means for providing a warning signal after a predetermined alarm time, and

a controller connected to said gas flow temperature sensing means, said heating means temperature sensing means and said heating means power utilization sensing means, said controller configured to;

i) determine a difference temperature by subtracting the gas temperature determined by said gas flow temperature sensing means from the temperature sensed by said temperature sensing means,

ii) determine a power requirement value for the heating means from said heating means power utilisation sensing means,

iii) calculate a thermal conductivity value by dividing said power requirement value by said difference temperature,

iv) activate said alarm means if said calculated thermal conductivity value is less than a predetermined minimum allowable thermal conductivity value,

wherein said controller provides that said humidification apparatus is configured to sense the temperature of the heating means, sense the gas flow temperature and sense the power used by said heating means and calculate thermal conductivity based on what is sensed, and output an alarm depending on the calculated thermal conductivity.

2. Humidification apparatus as claimed in claim 1 which also comprises flow probe means for sensing the flow rate of said gas flow and storage means for storing a number of said predetermined minimum allowable thermal conductivity values with associated gas flow rates, and said controller is also configured to carry out the step of

iii a) determining the gas flow rate from said flow probe means and obtaining from said storage means the predetermined minimum allowable thermal conductivity value associated with the determined gas flow rate.

3. Humidification apparatus as claimed in claim 1 or claim 2 wherein said controller is also configured to carry out the step of

v) waiting a predetermined period of time and then repeating steps (i) to (v).

4. Humidification apparatus as claimed in claim 2 wherein said flow probe means comprises:

sensor housing means for positioning in said gas flow, said sensor housing means having a longitudinal axis substantially perpendicular to said humidified gas flow and a sensing end,

sensing means for sensing said gas flow housed within said sensor housing means at or near said sensing end, and

at least one projecting tab means extending laterally from said sensor housing means for providing surfaces which enable liquid condensate to disperse away from said sensing end of said sensor housing means.

5. Humidification apparatus as claimed in claim 4 wherein said flow probe means comprise two or more said projecting tab means.

6. Humidification apparatus as claimed in claim 5 wherein said two projecting tab means are oppositely positioned around said sensor housing means.

7. Humidification apparatuses claimed in claim 4 or claim 5 wherein each said at least one projecting tab means is aligned parallel to said gas flow.

8. Humidification apparatus as claimed in claim 4 or claim 5 wherein liquid condensate is dispersed along the lines of intersection between said sensor housing means and said at least one projecting tab means, there existing a localised area of low surface tension along said lines of intersection.

9. Humidification apparatuses claimed in claim 4 or claim 8 wherein said sensor probe means comprise two sensor housing means being defined by a temperature sensor housing and a flow rate sensor housing.

10. Humidification apparatus as claimed in claim 9 wherein said sensing means of said temperature sensor housing and said flow rate sensor housing each comprise a temperature dependent resistance.

11. Humidification apparatus as claimed in claim 9 wherein said sensing means of said flow rate sensor housing is configured to be occasionally heated to a predetermined difference temperature above the temperature of said gas flow, and wherein the power required by said sensor means of said flow rate sensor housing to maintain said predetermined difference temperature providing an indication of the flow rate of said gas.

12. Humidification apparatus as claimed in claim 9 wherein said sensing means of said flow rate sensor housing is exposed at or near the sensing end of the flow rate sensor housing while the sensing means of said temperature sensor housing is encapsulated at or near the sensing end of the temperature sensor housing.

13. Humidification apparatus as claimed in claim 9 herein said temperature sensor housing and flow rate sensor housing are spaced across said gas flow in order that heat produced by the sensing means of said flow rate sensor housing has substantially minimal effect on the sensing means of said temperature sensor housing.

14. Humidification apparatus as claimed in claim 11 wherein said flow rate sensor housing is positioned downstream of said temperature sensor housing in order that heat produced by the sensing means of said flow rate sensor housing does not effect the sensing means of said temperature sensor housing.

15. Humidification apparatus as claimed in claim 2 wherein gas flow is channelled within a conduit of known cross-sectional area, at least in the region adjacent said flow probe means, and is provided with a sensor entry port adapted to receive said flow probe means, said sensor entry port being provided with a fixed locating depression and said flow probe means being provided with a complimentary fixed locating tooth, the positioning of said temperature and flow rate sensor housing means relative to said gas flow being controlled by the interconnection of said locating depression and tooth.