Respiratory humidification system

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).

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to gases distribution systems and in particular, though not solely, to respiratory humidifier systems which humidify gases for a patient, or other person in need of such gases, to breathe.

2. Description of the Prior Art

Many, if not all, existing respiratory humidification systems which deliver humidified gases (such as oxygen or anaesthetic gases) to a patient, or other person in need of such gases, operate as temperature controllers. That is, the temperature of the gases leaving the humidification device in the breathing circuit is monitored and the heat source controlled in response to changes in that temperature to achieve a desired outgoing humidified gases temperature. An example of this type of humidifier control system is disclosed in our prior U.S. Pat. No. 5,558,084. This method of control has a number of disadvantages including:

• • In situations with high incoming gases temperature (approaching the desired outgoing gases temperature) little heat is necessarily supplied to the gases by the humidification process to achieve the required temperature. Accordingly, little humidification of the gases is also achived.
  • The dependency on temperature sensors in this control method means that incorrect placement or connection of the temperature sensors can lead to impaired performance of the entire humidification and breathing system.
  • Lack of flow sensors which, if provided, would enable certain breathing circuit conditions to be easily recognised and appropriate action to be taken by the humidification device (and/or the gases supply). Flow sensors have previously not been utilised in humidification systems due to insufficient robustness and problems of condensation occurring on the flow sensor, leading to incorrect flow readings.
  • Gases being supplied to the patient at a pressure/humidity combination which is inappropriate. It is well known that certain humidity levels are required of gases which are to be administered to a patient. Different humidity values are specifically suitable to intact (for example face mask) or bypassed (intubation delivery of gases) airways. Temperature sensing alone can not ensure that these required temperature humidity values are achieved.
  • Some existing respiratory humidification devices require users to adjust dials which have little or no intuitive relationship to the actual physical parameters they are intended to control. Often the dials adjust the required gases outlet temperature and/or the heating supplied by the heater wire provided within the conduit connecting humidifier to patient (and sometimes also the conduit connecting the patient back to the gases supply). The most important parameter in humidified gases supply to a patient is the humidity of the gases as insufficient humidity can very quickly dehydrate the patient's airways. Accordingly, users have little or no idea where to position the dials to produce the desired result of optimum humidity in the supplied gases at the existing flow rate. An automated system in which the user need only inform the humidification device if the patient receiving the humidified gases has intact or by-passed airways would be a major advance.
  • Many existing respiratory humidification devices display the gases temperature being supplied to the patient. As previously mentioned, the most important parameter in respiratory humidification systems is the humidity of the gases. Often, the temperature displayed has no relationship to the actual humidity of the gases being supplied to the patient due to heating in the delivery circuit and can therefore be misleading to the average health care professional. It would, therefore, be an advantage if the temperature displayed was in some way related to or indicative of the humidity of the gases being supplied to the patient.

BRIEF SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a respiratory humidifier system which will go at least some way towards overcoming the above disadvantages or which at least provide the industry with a useful choice.

Accordingly, in a first aspect, the invention consists in sensor probe means adapted for positioning in a flow of humidified gases comprising:

• • sensor housing means adapted for positioning in said gases flow, said sensor housing means having a longitudinal axis substantially perpendicular to said humidified gases flow and a sensing end,
  • sensing means 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, said at least one projecting tab means providing surfaces which enable liquid condensate to disperse away from said sensing end of said sensor housing means.

In a second aspect, the invention consists in humidification apparatus for humidifying a gases flow to be supplied to a patient or other person in need of such gases comprising:

• • humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gases flow to pass through said humidification chamber means,
  • heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapour to said gases flow passing through said humidification chamber means,
  • gases transportation pathway means connected to said outlet of said humidification chamber means to convey said gases flow to said patient or other person in need of such gases,
  • flow probe means adapted to sense the flow rate of said gases flow, temperature sensing means adapted to sense the temperature of said gases flow,
  • user input means to allow a user to set a required temperature of said gases flow,
  • control means which receives input from said flow probe means, said temperature sensing means and said user input means and controls said heating means in response to said inputs to maintain said gases flow at said required temperature.

In a third aspect, the invention consists in humidification apparatus for humidifying a gases flow to be supplied to a patient or other person in need of such gases comprising:

• • humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gases flow to pass through said humidification chamber means,
  • heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapour to said gases flow passing through said 34, 35
    Where the value of “offset” is for example 3° C. and equates to the desired temperature gradient required along the conduit 14. It should be noted that the value of “offset” chosen is dependent on the physical properties and configuration of the conduit.

    For example, for an offset of 3° C. and a humidification chamber 4 outlet gases temperature of 37° C., the heater wire 15 will be energised appropriately (for example by adjusting its duty cycle) to maintain the temperature of gases supplied to the patient at 40° C. Similarly, if the chamber outlet temperature dropped to 31° C. then the temperature of gases supplied to the patient would be controlled to arrive at 34° C. In both instances, a temperature gradient or difference of +3° C. is maintained along the conduit minimising or eliminating condensation.

    If it is found that the required offset value is not maintainable (that is, the heater wire is incapable of raising the temperature of the gases in the conduit to the calculated required value sensed by, for example a temperature sensor near the patient end of conduit 14) then controller 11 will decrease the humidification chamber outlet temperature (by for example, reducing the duty cycle of power supplied to heater plate 9) in order to maintain the required offset temperature along the conduit. As an example, the controller could be programmed to begin to drop the humidification chamber outlet temperature in 0.5° C. steps (to a minimum of for example 35.5° C.) if the off-set temperature value is not maintainable at at least 2° C. for 15 minutes. For example, for an offset value of 3° C. and an initial chamber outlet temperature of 37° C., the gases supplied to the patient should be controlled to arrive at 40° C. If however the gases arriving at the patient are at 38.6° C. (an actual offset or difference of only 1.6° C.), then controller 11 will drop the humidification chamber outlet temperature to 36.5° C. after 15 minutes. The above calculations will then be repeated and if the temperature of gases reaching the patient is not maintainable at 39.5° C. then controller 11 will again consider dropping the humidification chamber temperature. This process will be repeated until a humidification chamber outlet temperature is reached at which the required conduit offset temperature can be maintained. Furthermore, the controller 11 could then attempt to raise the humidification chamber outlet gases temperature so that the gases supplied to the patient can again be established at a required temperature but only if this can be accomplished under the offset temperature constraint This would only be possible if ambient circumstances had changed.

    Thus, at least in the preferred form, the present invention incorporating all or some of the above described features provides a respiratory humidification system which enables humidity and/or temperature control of the humidified gases to be achieved. The gases flow probed according to one embodiment of the present invention enables accurate flow rate measurements to be made without condensation affecting the sensor. In part this increased accuracy is also due to the locating system which ensures correct alignment of the flow and/or temperature probe in the gases flow. Due to the ability to accurately sense flow rate with this flow sensor, the control systems according to the present invention are able to provide a gases flow to the patient which is controlled to a required humidity. The flow rate sensor also enables “automatic” control to be achieved whereby the user is not required to constantly monitor the output of the humidifier and to alter inputs to achieve desired changes, the user is merely required to inform the humidifier of the patient's gases delivery situation and the humidifier is able to provide the required gases temperature and humidity without further user input The humidifier also displays a gases temperature value which is clinically relevant to the gases reaching the patient. In addition, the respiratory humidification according to other preferred embodiments of the present invention encompasses various safety improvements over the prior art.

Claims

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

humidificaion chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gaseous flow to pass through said humidification chamber means,

heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapor to said gaseous flow passing through said humidification chamber means,

gaseous flow transportation pathway means connected to said outlet of said humidification chamber means to convey said gaseous flow to said patient or other person in need of such gaseous flow,

flow probe means adapted to sense the flow rate of said gaseous flow,

probe heating means adapted to heat at least a portion of said flow probe means,

temperature sensing means adapted to sense the temperature of said gaseous flow,

user input means to allow a user to set a required temperature of said gaseous flow,

control means which receives input from said flow probe means, said temperature sensing means and said user input means and controls said heating means in response to said inputs to maintain said gaseous flow at said required temperature.

2. humidification apparatus as claimed in claim 1 said control means is adapted to determine if the humidification apparatus is in a normal operating condition or if abnormal operation has occurred based on said temperature and/or said flow rate, wherein said normal condition in use relating to whether said temperature and/or said flow rate falling with a predetermined range.

3. humidification apparatus for humidifying a gaseous flow to be supplied to a patient or other person in need of such gaseous flow comprising:

humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gaseous flow to pass through said humidification chamber means,

gaseous flow transportation pathway means connected to said outlet of said humidification chamber means to convey said gaseous flow to said patient or other person in need of such gaseous flow,

flow probe means adapted to sense the flow rate of said gaseous flow including sensor housing means adapted for positioning in said gaseous flow, said sensor housing means having a longitudinal axis substantially perpendicular to said humidified gaseous flow and a sensing end, sensing means housed within said sensor housing means at or near said sensing end, and at least two projecting tab means extending laterally from said sensor housing means, oppositely positioned around said sensor housing means and aligned parallel to said gaseous flow, wherein liquid condensate is dispersed along the lines of intersection between said sensor housing means and said at least two tab means away from said sensing end of said sensor housing means, there existing a localized area of low surface tension along said lines of intersection,

temperature sensing means adapted to sense the temperature of said gaseous flow,

user input means to allow a user to set a required temperature of said gaseous flow,

control means which receives input from said flow probe means, said temperature sensing means and said user input means and controls said heating means in response to said inputs to maintain said gaseous flow at said required temperature.

4. humidification apparatus as claimed in claim 3 wherein said flow probe means comprise two sensor housing means, a temperature sensor housing means and a flow rate sensor housing means, each comprising a temperature dependent resistance,

and wherein said sensing means of said flow rate sensor housing means is occasionally heated to a predetermined difference temperature above the temperature of said gaseous flow, the power required by said sensor means of said flow rate sensor housing means to maintain said predetermined difference temperature providing an indication of the flow rate of said gaseous flow,

and wherein said sensing means of said flow rate sensor housing means is exposed at or near the sensing end of the flow rate sensor housing means up down stream of and spaced across said gaseous flow from the sensing means of said temperature sensor housing means is encapsulated at or near the sensing end of the temperature sensor housing means, in order that heat produced by the sensing means of said flow rate sensor housing means does not effect the sensing means of said temperature sensor housing means.

5. humidification apparatus as claimed in claim 3 wherein said gaseous flow transportation pathway means has a 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 gaseous flow being controlled by the interconnection of said locating depression and tooth.

6. humidification apparatus for humidifying a gaseous flow to be supplied to a patient or other person in need of such gaseous flow comprising:

humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gaseous flow to pass through said humidification chamber means,

heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapor to said gaseous flow passing through said humidification chamber means, said heating means utilizing a measurable quantity of power,

gaseous flow transportation pathway means connected to said outlet of said humidification chamber means to convey said gaseous flow to said patient or other person in need of such gaseous flow,

flow probe means adapted to sense the flow rate of said gaseous flow,

control means which receives input from said flow probe means and including storage means which is programmed to:

i.) calculate the power usage required of said heating means in order to humidify said gaseous flow to a predetermined level at the gaseous flow rate sensed by said flow probe means,

ii.) determine the power presently being utilized by said heating means, and

iii.) supply said predetermined level of power to said heating means if the determined present power utilization of said heating means is less than said required power usage.

7. humidification apparatus as claimed in claim 6 wherein said step of calculating the power usage required of said heating means in order to humidify said gaseous flow comprises sensing the present gaseous flow by said flow probe means and searching in a data storage means for a previously stored power value associated with said sensed gaseous flow rate, said data storage means being previously supplied with flow rate and associated power usage values.

8. humidification apparatus as claimed in claim 6 or claim 7 wherein said step of calculating the power usage required of said heating means in order to humidify said gaseous flow also comprises the steps of calculating the rate of evaporation required in order to attain said predetermined level at the sensed gaseous flow rate and then determining the power required of said heating means to produce the required said rate of evaporation.

9. humidification apparatus as claimed in claim 6 or claim 7 wherein said humidification apparatus also comprises a temperature sensing means adapted to sense the temperature of said gaseous flow leaving said humidification chamber means and to supply a temperature signal to said control means and said program stored by said control means includes, between said steps (ii) and (iii), the step of:

a) controlling the energization of said heating means in order to maintain said gaseous flow rate exciting said humidification chamber means at a predetermined temperature.

10. humidification apparatus as claimed in claim 6 or claim 7 wherein said program stored by said control means also comprise the subsequent step of:

i.) sensing the temperature of the gaseous flow leaving the humidification chamber means and returning to step (c) when the sensed temperature is less than said predetermined temperature.

11. humidification apparatus as claimed in claim 6 or claim 7 wherein said flow probe means comprises:

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

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

at least two projecting tab means extending laterally from said sensor housing means, oppositely positioned around said sensor housing means and aligned parallel to said gaseous flow, wherein liquid condensate is dispersed along the lines of intersection between said sensor housing means and said at least two tab means away from said sensing end of said sensor housing means, there existing a localized area of low surface tension along said lines of intersection.

12. humidification apparatus as claimed in claim 11 wherein said flow probe means comprise two sensor housing means, a temperature sensor housing means and a flow rate sensor housing means, each comprising a temperature dependent resistance,

and wherein said sensing means of said flow rate sensor housing means is occasionally heated to a predetermined difference temperature above the temperature of said gaseous flow, the power required by said sensor means of said flow rate sensor housing means to maintain said predetermined difference temperature providing an indication of the flow rate of said gaseous flow,

and wherein said sensing means of said flow rate sensor housing means is exposed at or near the sensing end of the flow rate sensor housing means up down stream of and spaced across said gaseous flow from the sensing means of said temperature sensor housing means is encapsulated at or near the sensing end of the temperature sensor housing means, in order that heat produced by the sensing means of said flow rate sensor housing means does not effect the sensing means of said temperature sensor housing means.

13. humidification apparatus as claimed in claim 11 wherein said gaseous flow transportation pathway means has a 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 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 gaseous flow being controlled by the interconnection of said locating depression and tooth.

14. humidification apparatus for humidifying a gaseous flow to be supplied to a patient or other person in need of such gaseous flow comprising:

humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gaseous flow to pass through said humidification chamber means,

heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapor to said gaseous flow passing through said humidification chamber means,

gaseous flow transportation pathway means connected to said outlet of said humidification chamber means to convey said gaseous flow to said patient or other person in need of such gaseous flow,

flow probe means adapted to sense the flow rate of said gaseous flow,

temperature sensing means adapted to sense the temperature of said gaseous flow in or adjacent said humidification chamber means,

user input means to allow a user to select a desired gaseous flow humidity level of said gaseous flow configured such that in use said desired gaseous flow humidity level is substantially on delivery to said patient,

data storage means containing information on target gaseous flow temperatures for various gaseous flow rates for a number of humidification chamber outlet means temperatures,

control means configured to receive input from said temperature sensing means and said user input means and configured to repeatedly obtain corresponding target temperature information from said data storage means corresponding to the desired gaseous flow humidity level in relation to said flow rate and configured to vary the heat provided by said heating means until the sensed temperature is substantially equivalent to said target temperature in order to substantially obtain said desired gaseous flow humidity level on delivery to said patient.

15. humidification apparatus as claimed in claim 14 wherein said gaseous flow transportation pathway means includes a heating wire means adapted to, upon energization to a setting determined by said control means, supply heat to said gaseous flow between said humidification means outlet and said patient or other person in need to such gaseous flow and wherein said control means thereby controls temperature changes in said gaseous flow along said gaseous flow transportation pathway, said control means adjusting said setting of said heating wire to control the temperature of said gaseous flow delivered to said patient or other person in need of such gaseous flow to a user set desired temperature.

16. humidification apparatus for humidifying a gaseous flow to be supplied to a patient or other person in need of such gaseous flow comprising:

humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gaseous flow to pass through said humidification chamber means,

heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapor to said gaseous flow passing through said humidification chamber means,

gaseous flow transportation pathway means connected to said outlet of said humidification chamber means to convey said gaseous flow to said patient or other person in need of such gaseous flow,

flow probe means adapted to sense the flow rate of said gaseous flow,

temperature sensing means adapted to sense the temperature of said gaseous flow,

user input means to allow a user to select a desired gaseous flow humidity level of said gaseous flow,

data storage means containing information on target gaseous flow temperatures at various gaseous flow rates for a number of humidification chamber outlet means temperatures,

control means which receives input from said temperature sensing means and said user input means and using said flow information from said flow probe means repeatedly obtains corresponding target temperature information from said data storage means corresponding to the desired gaseous flow humidity level and varies the heat provided by said heating means until the sensed temperature is substantially equivalent to said target temperature in order to obtain said desired gaseous flow humidity level,

wherein said flow probe means comprising:

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

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

at least two projecting tab means extending laterally from said sensor housing means, oppositely positioned around said sensor housing means and aligned parallel to said gaseous flow, wherein liquid condensate is dispersed along the lines of intersection between said sensor housing means and said at least two tab means away from said sensing end of said sensor housing means, there existing a localized area of low surface tension along said lines of intersection.

17. humidification apparatus as claimed in claim 16 wherein said gaseous flow transportation pathway means includes a heating wire means adapted to, upon energization to a setting determined by said control means, supply heat to said gaseous flow between said humidification means outlet and said patient or other person in need to such gaseous flow and wherein said control means thereby controls temperature changes in said gaseous flow along said gaseous flow transportation pathway, said control means adjusting said setting of said heating wire to control the temperature of said gaseous flow delivered to said patient or other person in need of such gaseous flow to a user set desired temperature.

18. humidification apparatus as claimed in claims 16 or 17 wherein said flow probe means comprise two sensor housing means, a temperature sensor housing means and a flow rate sensor housing means, each comprising a temperature dependent resistance,

and wherein said sensing means of said flow rate sensor housing means is occasionally heated to a predetermined difference temperature above the temperature of said gaseous flow, the power required by said sensor means of said flow rate sensor housing means to maintain said predetermined difference temperature providing an indication of the flow rate of said gaseous flow,

and wherein said sensing means of said flow rate sensor housing means is exposed at or near the sensing end of the flow rate sensor housing means up down stream of and spaced across said gaseous flow from the sensing means of said temperature sensor housing means is encapsulated at or near the sensing end of the temperature sensor housing means, in order that heat produced by the sensing means of said flow rate sensor housing means does not effect the sensing means of said temperature sensor housing means.

19. humidification apparatus s claimed in claims 16 or 17 wherein said gaseous flow transportation pathway means has a 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 gaseous flow being controlled by the interconnection of said locating depression and tooth.

20. humidification apparatus for humidifying a gaseous flow to be supplied to a patient or other person in need of such gaseous flow comprising:

humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gaseous flow to pass through said humidification chamber means,

heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapor to said gaseous flow passing through said humidification chamber means,

gaseous flow transportation pathway means connected to said outlet of said humidification chamber means to convey said gaseous flow to said patient or other person in need of such gaseous flow,

flow probe means adapted to sense the flow rate of said gaseous flow, and

control means configured to receive input from said flow probe means and configured to compare the sensed flow rate of said gaseous flow with a predetermined minimum required gaseous flow rate and configured to place the humidification apparatus into a safe mode of operation if the sensed rate is less than said predetermined minimum rate, said safe mode including conditional logic which is configured to choose between a predetermined set of actions at least relating to the energization of said heating means.

21. humidification apparatus as claimed in claim 20 wherein said predetermined minimum required gaseous flow rate is about 1.5 liters per minute.

22. humidification apparatus as claimed in claim 20 or claim 21 wherein heating plate temperature sensing means are also provided and said set of actions includes said control means energizing said heating means in such a way as to ensure that the temperature of said heating means does not exceed a predetermined maximum temperature.

23. humidification apparatus as claimed in claim 20 or claim 21 wherein said set of actions includes said control means limiting the power supplied to said heating means to a predetermined maximum level.

24. humidification apparatus for humidifying a gaseous flow to be supplied to a patient or other person in need of such gaseous flow comprising:

humidification chamber means adapted to hold a quantity of water and having an inlet and an outlet to allow said gaseous flow to pass through said humidification chamber means,

heating means provided adjacent said humidification chamber means and adapted to provide heat to said quantity of water in said humidification chamber means in order to provide water vapor to said gaseous flow passing through said humidification chamber means,

gaseous flow transportation pathway means connected to said outlet of said humidification chamber means to convey said gaseous flow to said patient or other person in need of such gaseous flow,

flow probe means adapted to sense the flow rate of said gaseous flow, and

control means which receives input from said flow probe means and compares the sensed flow rate of said gaseous flow with a predetermined minimum required gaseous flow rate and places the humidification apparatus into a safe mode of operation if the sensed rate is less than said predetermined minimum rate

wherein said flow probe means comprises:

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

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

at least two projecting tab means extending laterally from said sensor housing means, oppositely positioned around said sensor housing means and aligned parallel to said gaseous flow, wherein liquid condensate is dispersed along the lines of intersection between said sensor housing means and said at least two tab means away from said sensing end of said sensor housing means, there existing a localized area of low surface tension along said lines of intersection.

25. humidification apparatus as claimed in claim 24 wherein said predetermined minimum required gaseous flow rate is about 1.5 liters per minute.

26. humidification apparatus as claimed in claim 24 or 25 wherein said flow probe means comprise two sensor housing means, a temperature sensor housing means and a flow rate sensor housing means, each comprising a temperature dependent resistance,

and wherein said sensing means of said flow rate sensor housing means is occasionally heated to a predetermined difference temperature above the temperature of said gaseous flow, the power required by said sensor means of said flow rate sensor housing means to maintain said predetermined difference temperature providing an indication of the flow rate of said gaseous flow,

and wherein said sensing means of said flow rate sensor housing means is exposed at or near the sensing end of the flow rate sensor housing means up down stream of and spaced across said gaseous flow from the sensing means of said temperature sensor housing means is encapsulated at or near the sensing end of the temperature sensor housing means, in order that heat produced by the sensing means of said flow rate sensor housing means does not effect the sensing means of said temperature sensor housing means.

27. humidification apparatus as claimed in claims 24 or 25 wherein said gaseous flow transportation pathway means has a 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 gaseous flow being controlled by the interconnection of said locating depression and tooth.