WO2009085995A1

WO2009085995A1 - Systems and methods for controlling a heated humidifier

Info

Publication number: WO2009085995A1
Application number: PCT/US2008/087505
Authority: WO
Inventors: Yves Gaudard; Benjamin Desfossez; Hossein Nadjafizadeh; Veronique Grillier-Lanoir
Original assignee: Nellcor Puritan Bennett Llc
Priority date: 2007-12-28
Filing date: 2008-12-18
Publication date: 2009-07-09
Also published as: CA2707623A1; CA2707623C; EP2231246A1

Abstract

Systems and methods for controlling a heated humidifier are disclosed. A method may include determining an approximate flow rate of gas flow in a conduit in fluid communication with a heated humidifier and controlling the power delivered to the heated humidifier based at least on the approximate flow rate.

Description

SYSTEMS AND METHODS FOR CONTROLLING A HEATED

HUMIDIFIER

TECHNICAL FIELD

[0001] The invention relates to breathing assistance systems (e.g., ventilators or CPAP devices), and more particularly to systems and methods for controlling power delivered to a humidifier for use in a breathing assistance system.

BACKGROUND

[0002] A breathing assistance system typically delivers pressurized breathable gas to a patient via tubing called a "patient interface" or a "breathing circuit." The breathable gas typically includes air and/or one or more gasses (e.g., oxygen mixed with the air). The breathing assistance device typically increases the pressure in the breathing circuit so that the breathable gas is pushed into the lungs for inspiration, and then reduces the pressure in the breathing circuit so that gases in the lungs can be expired and vented to the atmosphere. Typically, one or more breathing assistance device parameters may be determined and/or adjusted prior to and/or during operation of the breathing assistance device. Such breathing assistance device parameters may include e.g., the mode of ventilation (e.g., CMV (controlled mandatory ventilation), SIMV (synchronized intermittent mandatory ventilation), CPAP (constant positive airway pressure), or bi-level CPAP); the patient's tidal volume (the volume of gas inspired with each breath); the respiratory rate (the number of breaths per minute (BPM)); and/or the O₂ concentration, flow rate, airway pressure, and/or minute volume (the volume inspired and expired in one minute) of breathable gas delivered to the patient.

[0003] The breathable gas delivered to the patient from the ventilator may be humidified and heated in the breathing circuit before being delivered to the patient. Humidification of the breathable gas is common in mechanical ventilation and/or CPAP treatment, particularly where the upper airway is bypassed. Humidification may prevent various conditions in the patient, e.g., hypothermia, inspissation of airway secretions, destruction of airway epithelium, and atelectasis. [0004] Humidifiers can be passive or active. Passive humidifiers (e.g., a heat-and- moisture exchanger (HME), which may be referred to as an "artificial nose") trap heat and humidity from the patient's exhaled gas and return some of that to the patient on the subsequent inhalation. Active, or heated, humidifiers pass all or a portion of the breathable gas through or over a heated water bath to increase the heat and water vapor content of the gas.

[0005] common problem associated with heated humidifiers is that the difference in temperature between the heated humidified breathable gas and the ambient temperature may cause water condensation to form in the breathing circuit. Such water condensation in a breathing circuit may be undesirable, as the patient may aspirate the condensed water. Furthermore, spilled water may damage electronic and/or other components of the humidifier or attached apparatus (e.g., a ventilator or CPAP device).

[0006] Another common problem associated with heated humidifiers is that a heater used to heat the water bath may reach high temperatures. This may occur particularly in situations in which the flow of breathable gas from the breathing assistance system is low. Air passed over the water bath may cool the water bath and the heater via convection. However, when air flow is low, heat may not be effectively dissipated by air flow convection. Increased temperatures may cause injuries to a patient and/or operator of a heated humidifier or a breathing assistance system including a heated humidifier. In addition, increased temperatures may also cause condensation in the breathing circuit.

SUMMARY

[0007] In accordance with the teachings of the present disclosure, disadvantages and problems associated with the operation of a heated humidifier may be substantially reduced or eliminated.

[0008] In accordance with one embodiment of the present disclosure, a method for controlling a heated humidifier is provided. The method may include determining an approximate flow rate of gas flow in a conduit in fluid communication with a heated humidifier and controlling the power delivered to the heated humidifier based at least on the approximate flow rate. [0009] In accordance with another embodiment of the present disclosure, a breathing assistance system may include a gas delivery system, a patient interface, a connection system, a heated humidifier, and a control system. The gas delivery system may be operable to supply breathable gas. The patient interface may be configured to interface with a patient for delivering breathable gas to the patient. The connection system may be configured to communicate breathable gas supplied by the gas delivery system to the patient interface for delivery to the patient. The heated humidifier may be coupled to at least one of the patient interface and the connection system, and may be configured to humidify the breathable gas. The control module may be configured to determine an approximate flow rate of breathable gas in the breathing assistance system and control an amount of power delivered to the heated humidifier based at least on the approximate flow rate.

[0010] In accordance with a further embodiment of the present disclosure, a humidification system may include a reservoir and a heater. The reservoir may be operable to contain a fluid and configured to interface with a conduit in fluid communication with the reservoir. The heater may be coupled to the reservoir and configured to heat the fluid to humidify a gas flowing through the conduit and generate heat as a function of an approximate flow rate of the gas in the conduit. [0011] In accordance with yet another embodiment of the present disclosure, a system for controlling a heated humidifier may include a flow detector and a control module. The flow detector may be operable to measure a flow rate of a gas flowing in a conduit in fluid communication with a heated humidifier. The control module may be coupled to the flow detector and configured to control the power delivered to the heated humidifier based at least on the measured flow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete understanding of the present embodiments may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

[0013] FIGURE 1 illustrates a block diagram of an example breathing assistance system with control of a heated humidifier, in accordance with the present disclosure; [0014] FIGURE 2 illustrates a flow chart of an example method for controlling the power delivered to a heated humidifier as a function of a temperature associated with the heated humidifier, in accordance with the present disclosure; and [0015] FIGURE 3 illustrates a flow chart of an example method for controlling the power delivered to a heated humidifier as a function of an approximate air flow associated with the heated humidifier, in accordance with the present disclosure.

DETAILED DESCRIPTION

[0016] Embodiments of the disclosure are best understood by reference to FIGURES 1 through 3, wherein like numbers are used to indicate like and corresponding parts.

[0017] FIGURE 1 illustrates a block diagram of an example breathing assistance system 10 with control of a heated humidifier in accordance with the present disclosure. In general, the heated humidifier control may limit the temperature of a heated humidifier and/or limit the power delivered to a heated humidifier in order to reduce and/or eliminate overheating of the heated humidifier and/or undesirable condensation in a breathing circuit.

[0018] As used herein, the terms "gas" and/or "breathable gas" may refer to any one or more gases and/or vaporized substances suitable to be delivered to and/or from a patient via one or more breathing orifices (e.g., the nose and/or mouth), such as air, nitrogen, oxygen, any other component of air, CO₂, vaporized water, vaporized medicines, and/or any combination of two or more of the above, for example. [0019] As used herein, the term "patient" may refer to any person or animal that may receive breathing assistance from system 10, regardless of the medical status, official patient status, physical location, or any other characteristic of the person. Thus, for example, patients may include persons under official medical care (e.g., hospital patients), persons not under official medical care, persons receiving care at a medical care facility, persons receiving home care, etc.

[0020] As shown in FIGURE 1, breathing assistance system 10 may be generally configured to provide breathing assistance (e.g., providing ventilation and/or treating an apnea or other breathing condition) to a patient 30. For example, breathing assistance system 10 may comprise a ventilator, a respirator, a CPAP device, or BiPAP device. Breathing assistance system 10 may include a gas flow source 20, a connection system 22, a patient interface 24, a humidifier 28, a flow detector 40, a temperature detector 42, a control module 44, and a power source 46. Gas flow source 20 may comprise any system or device suitable for generating and/or delivering pressurized gas (e.g., air and/or oxygen or one or more other supplemental gasses) toward patient 30, including without limitation, a blower, a compressor, a piston-based device, one or more pressurized gas tanks, one or more gas lines (e.g., from a wall or other source), or any combination thereof. Further, in embodiments with one or more gas lines supplying gas to breathing assistance system 10, gas flow source 20 may comprise one or more valves (e.g. solenoid or other valves) configured to control the volume and/or pressure of gas delivered towards patient 30. [0021] Connection system 22 may include any system or device suitable for delivering pressurized gas generated by gas flow source 20 towards patient 30, e.g., a patient circuit or breathing circuit (e.g., a single- or dual-limb patient circuit) and/or other conduits and connection devices. In some embodiments, connection system 22 may include a proximal pressure line operable to detect gas pressure near patient 30 in connection system 22 or patient interface 24. Patient interface 24 may include any system or device suitable for further delivering pressurized gas delivered by connection system 22 to patient 30, e.g., a nasal or face mask, nasal pillows, and/or a tube (e.g., an endotracheal tube, a tracheostomy tube and/or other tracheal tube). [0022] Humidifier 28 may be generally operable to humidify (e.g., to increase the heat and/or water vapor content of) breathable gas to be delivered to a patient 30. In the depicted embodiment, humidifier 28 may be an active, or heated, humidifier. In some embodiments, humidifier 28 may be integrated with, connected to, or otherwise associated with, breathing assistance system 10. For example, humidifier 28 may be permanently or removably attachable to breathing assistance system 10. In some embodiments, humidifier 28 may be communicatively coupled (permanently or removably) to connection system 22 such that humidifier 28 may humidify gas being delivered to patient 30 via connection system 22. Humidifier 28 may be coupled to connection system 22 in any suitable manner.

[0023] In other embodiments, humidifier 28 may not be associated with a breathing assistance system 10, For example, humidifier 28 may be used as a stand-alone humidifier (e.g., to provide humidified air to a patient) or in association with any other system using humidified gasses.

[0024] As depicted in FIGURE 1, humidifier 28 may include a reservoir 32 and a heater 34. Reservoir 32 may be any system, device, or apparatus operable to contain water and/or other fluid. Heater 34 may be coupled to reservoir 34 and may be any system, device, or apparatus (e.g., a heated coil) operable to heat water and/or other fluid in reservoir 32 in order to humidify gas delivered to patient 30. In certain embodiments, heater 34 may be powered via electrical current. [0025] Flow detector 40 may generally be operable to detect the flow rate of gas flowing through one or more conduits of system 10, e.g., the flow rate produced by gas flow soui"ce 20 or the flow rate of gas delivered to patient 30. Flow detector 40 may include any number of sensors operable to detect flow rate of a gas and/or any device operable to convert a detected flow rate into electrical signals or otherwise sense flow rate. Flow detector 40 may be placed at any suitable location and in any suitable orientation for sensing flow rate of a gas within breathing assistance system 10. For example, flow detector 40 may be placed within connection system 22, or near gas flow source 20, an air intake port, and/or an air outlet port. [0026] Temperature detector 42 may generally be operable to measure a temperature associated with humidifier 28 and/or gas humidified by humidifier 28. Temperature detector 42 may include any number of sensors operable to measure temperature and/or any suitable device operable to convert a detected temperature into electrical signals or otherwise sense temperature. Temperature detector 42 may be placed at any suitable location and in any suitable orientation for sensing temperature associated with humidifier 28 and/or gas humidified by humidifier 28. For example, temperature detector 42 may be placed in, on, or near heater 34 to detect a temperature associated with heater 34 (e.g., the temperature of a portion of heater 34 in contact with reservoir 32). In a different embodiment, temperature detector 42 may be placed in, on, or near reservoir 32 to detect a temperature associated with reservoir 32 (e.g., the temperature of water and/or other fluid within reservoir 32). In yet another embodiment, temperature detector 42 may be placed within connection system 22 in order to detect the temperature of humidified gas delivered to patient 30. [0027] Control module 44 may generally be operable to process various inputs, e.g., inputs from user interface 50 (see below), feedback from flow detector 40, temperature detector 42, and/or other variables sensed or otherwise detected by other sensors associated with breathing assistance system 10, and to regulate the temperature of one or more components of humidifier 28 and/or the amount of power delivered to humidifier 28. Control module 44 may include any suitable system or device for controlling the operation of breathing assistance system 10, humidifier 28, and/or other components of breathing assistance system 10, including, e.g., a microcontroller, a digital signal processor (DSP), an application specific integrated controller (ASIC), electrically-programmable read-only memory (EPROM), or a field-programmable gate array (FPGA).

[0028] In some embodiments, control module 44 may include software and/or other executable code for analyzing and/or feedback from user interface 50, flow detector 40, pressure detector 42, or other variables sensed or otherwise detected by other sensors associated with breathing assistance system 10 to generate control signals for regulating the operation of breathing assistance system 10 humidifier 28, and/or other components of breathing assistance system 10. Such software may include any suitable algorithms, logic and/or instructions for processing signals in breathing assistance system 10, and may be stored in any suitable data storage media. In some embodiments, for example those in which control module 44 comprises an FPGA, the functionality of such software may be programmed into the FPGA rather than provided as separate software.

[0029] Power source 46 may include any system, device, or apparatus operable to supply electrical power to one or more components of breathing assistance system 10, In certain embodiments, power source 46 may include a battery. In the same or alternative embodiments, power source 46 may provide alternating current to one or more components of breathing assistance system 10, In addition, power source 46 may include an AC/DC adaptor that may convert 120- or 240~volt (or any other suitable voltage) alternating current supplied by a utility company to a regulated direct current power source. In the same or alternative embodiments, an AC/DC adaptor may also charge a battery while supplying power to breathing assistance system 10. [0030] Although each of flow detector 40, temperature detector 42, control module 44 and power source 46 are depicted as components separate from humidifier 28, it is understood that in certain embodiments of the present disclosure, humidifier 28 may include one or more of flow detector 40, temperature detector 42, control module 44 and power source 46. In addition, although FIGURE 1 depicts one flow detector 40, one temperature detector 42, one central system 44, and one power source 46, breathing assistance system 10 may include any suitable number of such components. [0031] User interface 50 may include any suitable device or devices allowing a user to interface with breathing assistance system 10, e.g., to input desired performance parameters that may be communicated to control module 44 to control the operation of gas flow source 20, humidifier 28 and/or other components of breathing assistance system 10. For example, user interface 50 may allow a user to input one or more of the following performance parameters: the age, weight, tidal volume capacity, respiratory rate, inhale sensitivity, exhale sensitivity, circuit leak, rise time, alarm settings, delay, ramp, starting pressure, inhalation:exhalation (I:E) ratio, and/or other characteristics of patient 30, a desired gas flow rate to patient 30, desired gas pressure or pressures to patient 30, desired humidity of gas delivered to patient 30, maximum operating temperature of humidifier 28, a selected ventilation program, and/or other parameters. For example, user interface 50 may include a screen, touch screen, keypad, battery, and/or any combination thereof.

[0032] FIGURE 2 illustrates a flow chart of an example method 60 for controlling the power delivered to humidifier 28 as a function of a temperature associated with humidifier 28, in accordance with the present disclosure. In one embodiment, method 60 includes measuring a temperature associated with humidifier 28, determining whether such temperature is above or below a predetermined maximum temperature, and controlling (e.g., starting or stopping) the delivery of power to humidifier 28 in response to the determination. Method 60 may operate to limit a temperature associated with humidifier 28, thereby preventing humidifier 28 and/or its components from overheating and potentially causing damage and/or injury and/or preventing undesirable condensation in a breathing circuit.

[0033] According to one embodiment, method 60 preferably begins at step 62. As noted above, teachings of the present disclosure may be implemented in a variety of configurations of breathing assistance system 10. As such, the preferred initialization point for method 60 and the order of the steps 62-74 comprising method 60 may depend on the implementation chosen.

[0034] At step 62, control module 44 may control power source 46 to deliver power to humidifier 28. At step 64, temperature detector 42 and/or control module 44 may measure a temperature associated with humidifier 28. For example, in certain embodiments temperature detector 42 and/or control module 44 may measure a temperature associated with heater 34 (e.g., the temperature of a portion of heater 34 in contact with reservoir 32). In a different embodiment, temperature detector 42 and/or control module 44 may measure a temperature associated with reservoir 32 (e.g., the temperature of water and/or other fluid within reservoir 32). In yet another embodiment, temperature detector 42 and/or control module 44 may measure the temperature of humidified gas in connection system 22.

[0035J At step 66, control module 44 may determine whether the temperature measured at step 64 is above a predetermined maximum temperature. The predetermined maximum temperature may be set or established in any suitable manner. For example, in certain embodiments, the predetermined maximum temperature may be permanently set by a manufacturer. In other embodiments, the predetermined maximum temperature may be selectively adjustable (e.g., by a patient or caregiver) via user interface 50. In the same or alternative embodiments, the predetermined maximum temperature may be selected based on experimentation, e.g., experimentation by a manufacturer, patient, or caregiver.

[0036] If it is determined at step 66 that the measured temperature is above the predetermined maximum temperature, method 60 may proceed to step 68 where the delivery of power to humidifier 28 may be stopped. Otherwise, if it is determined at step 66 that the temperature is not above the predetermined maximum temperature, method 60 may return to step 64, such that steps 64 and 66 may be repeated until such time as the measured temperature rises above the predetermined maximum temperature.

[0037] At step 68, control module 44 may stop power delivery from power source 46 to humidifier 28. This may be performed in any suitable manner. For example, control module 44 may cause a mechanical and/or electrical switch supplying power from power supply to humidifier 28 to open, thus preventing the delivery of electrical current to humidifier 28.

[0038] At step 70, temperature detector 42 and/or control module 44 may measure a temperature associated with humidifier 28. For example, in certain embodiments temperature detector 42 and/or control module 44 may measure a temperature associated with heater 34 (e.g., the temperature of a portion of heater 34 in contact with reservoir 32). In a different embodiment, temperature detector 42 and/or control module 44 may measure a temperature associated with reservoir 32 (e.g., the temperature of water and/or other fluid within reservoir 32). In yet another embodiment, temperature detector 42 and/or control module 44 may measure the temperature of humidified gas in connection system 22.

[0039] At step 72, control module 44 may determine whether the temperature measured at step 64 is below a predetermined humidifier restart temperature. The predetermined humidifier restart temperature may be set or established in any suitable manner. For example, in certain embodiments, the predetermined humidifier restart temperature may be permanently set by a manufacturer. In other embodiments, the predetermined humidifier restart temperature may be selectively adjustable (e.g., by a patient or a caregiver) via user interface 50. In the same or alternative embodiments, the predetermined humidifier restart temperature may be selected based on experimentation, e.g., experimentation by a manufacturer, patient or caregiver. If it is determined at step 72 that the measured temperature is below the predetermined humidifier restart temperature, method 60 may proceed to step 74 where the delivery of power to humidifier 28 may begin. Otherwise, if it is determined at step 72 that the temperature is not below the predetermined humidifier restart temperature, method 60 may again return to step 72, such that steps 72 and 74 may be repeated until such time as the measured temperature falls below the predetermined humidifier restart temperature.

[0040] In some embodiments, the predetermined humidifier restart temperature may be equal to the predetermined maximum temperature. However, in such embodiments, the existence of only one threshold temperature for both the powering on and powering off of humidifier 28 may lead to excessive and unnecessary cycling of heater 34. For example, a measured temperature below the predetermined maximum temperature, humidifier 28 will remain powered on. However, as the measured temperature rises above the predetermined maximum temperature, power from humidifier 28 may be withdrawn. If the predetermined maximum temperature is the same as the predetermined humidifier restart temperature, the smallest temperature drop following the powering off of humidifier 28 will cause the temperature to drop below the predetermined humidifier restart temperature and powering on of humidifier 28, As a result, heater 34 may be cycled on and off at a rapid pace, which may adversely affect the longevity of components within humidifier 28 due to the continuous cycling. Accordingly, in some embodiments the predetermined maximum temperature is greater than the predetermined humidifier restart temperature.

[0041] At step 74, control module 44 may restart power delivery from power source 46 to humidifier 28. This may be performed in any suitable manner. For example, control module 44 may cause a mechanical and/or electrical switch supplying power to humidifier 28 to close, thus enabling the delivery of electrical current from power source 46 to humidifier 28. After completion of step 74, method 60 may return to step 64, where the temperature may be measured to determine if it exceeds the predetermined maximum temperature.

[0042] Although FIGURE 2 discloses a particular number of steps to be taken with respect to method 60, it is understood that method 60 may be executed with greater or lesser steps than those depicted in FIGURE 2. In addition, although FIGURE 2 discloses a certain order of steps to be taken with respect to method 60, the steps comprising method 60 may be completed in any suitable order. Method 60 may be implemented using breathing assistance system 10 or any other system operable to implement method 60. hi certain embodiments, method 60 may be implemented partially or fully in software embodied in tangible computer readable media. [0043] FIGURE 3 illustrates a flow chart of an example method 80 for controlling the power delivered to a heated humidifier as a function of an air flow associated with the heated humidifier, in accordance with the present disclosure. In one embodiment, method 80 includes determining an appropriate flow rate of breathable gas being delivered to patient 30, and delivering power to humidifier 28 based at least on the approximate flow rate. As mentioned above, when the flow rate of breathable gas delivered to patient 30 is low, less heat dissipates from humidifier 28 via convection. Accordingly, method 80 may reduce the likelihood of humidifier 28 or its components overheating when the flow rate is low, thus reducing the potential of damage and/or injury and/or preventing undesirable condensation in a breathing circuit. [0044] According to one embodiment, method 80 preferably begins at step 82. As noted above, teachings of the present disclosure may be implemented in a variety of configurations of breathing assistance system 10. As such, the preferred initialization point for method 80 and the order of the steps 82-88 comprising method 80 may depend on the implementation chosen.

[0045] At step 82, flow detector 40 and/or control module 44 may determine an appropriate flow rate of breathable gas delivered to patient 30. For example, flow detector 40 and/or control module 44 may measure a flow rate of gas within connection system 22. In another embodiment, control module 44 and/or another component of breathing assistance system 10 may estimate the flow rate, e.g., by determining the power delivered to gas flow source 20, by measuring the speed of the rotor of gas flow source 20 when the source is a blower, by sensing the pressure delivered to patient 30, and from various ventilation parameters set by a user. [0046] At step 84, control module 44 may determine whether the approximate flow rate determined at step 82 is below a predetermined threshold flow rate. The predetermined threshold flow rate may be set or established in any suitable manner. For example, in certain embodiments, the predetermined threshold flow rate may be permanently set by a manufacturer. In other embodiments, the predetermined threshold flow rate may be selectively adjustable (e.g., by a patient or a caregiver) via user interface 50. In the same or alternative embodiments, the predetermined threshold flow rate may be selected based on experimentation, e.g. experimentation by a manufacturer or caregiver.

[0047] If it is determined at step 84 that the approximate flow rate is not below the predetermined threshold flow rate, method 80 may proceed to step 86. Otherwise, if it is determined at step 84 that the measured temperature is below the predetermined threshold flow rate, method 80 may proceed to step 88.

[0048] At step 86, control module 44 may cause power to be delivered from power source 46 to humidifier 28 according to selected humidifier settings. For example, patient 30 or a caregiver may set one or more settings related to the operation of breathing assistance system 10 and/or humidifier 28 via user interface 50. One or more of such settings may affect the amount of power delivered from power source 46 to humidifier 28. As an example, patient 30 and/or a caregiver may set a desired humidity level for breathable gas to be delivered to patient 30. Based in part on the desired humidity level, a specified amount of power may be delivered to heater 34 in order to produce the desired humidity level. In situations where the approximate air flow determined at step 82 is above the predetermined threshold flow rate, heat may be earned away from humidifier 28 via convection, thus allowing humidifier 28 to operate in accordance with the selected humidifier settings without concern that humidifier 28 may overheat and/or that undesirable condensation may occur. [0049] However, in situations where the approximate air flow determined at step 82 is below the predetermined threshold flow rate, sufficient heat may not be carried away from humidifier 28 via convection, which may cause overheating of humidifier 28 and/or undesired condensation in connection system 22 (e.g., patient circuit) if power is delivered to humidifier 28 in accordance with the selected humidifier settings. Accordingly, at step 88, control module 44 may cause power to be delivered from power source 46 to humidifier 28 as a function of the approximate flow rate such that the power delivered at step 88 is lower than the power delivered at step 86. In certain embodiments, control module 44 may increase the power delivered at step 88 as the approximate flow rate increases and decreases the power delivered as the approximate flow rate decreases. In certain embodiments, the power delivered at steps 86 and 88 may governed by the following equation:

P_D = P₈ for R_Λ > R_T (step 86)

PD = Ps(nR_Λ + m) for R_A < RT (step 88)

where P_D is the power delivered, Ps is the power delivered according to humidifier settings at flow rates not below the predetermined flow rate threshold, R_A is the approximate flow rate, R_T is the predetermined flow rate threshold, and n and m are constants. Each of n and m may be selected based on experimentation, e.g., experimentation by a manufacturer or caregiver. The value of n may be selected so as to establish the rate or slope at which P_D varies as a function of R_A. The value of m may be selected so as to provide a minimum delivery of power (equal to mPs) as RA approaches zero.

[0050] Although FIGURE 3 discloses a particular number of steps to be taken with respect to method 80, it is understood that method 80 may be executed with greater or lesser steps than those depicted in FIGURE 3. For example, in certain embodiments, method 80 may not include steps 84 and 86, such that method 80 alternates between steps 82 and 88, In such embodiments control module 44 may cause power to be delivered from power source 46 to humidifier 28 as a function of the approximate flow rate, regardless of the value of the approximate flow rate (e.g.,

for all RA). In addition, although FIGURE 3 discloses a certain order of steps to be taken with respect to method 80, the steps comprising method 80 may be completed in any suitable order. Method 80 may be implemented using breathing assistance system 10 or any other system operable to implement method 80, In certain embodiments, method 80 may be implemented partially or fully in software embodied in tangible computer readable media.

[0051] In addition, although the equations set forth depict an embodiment whereby the relationship between power delivered to humidifier 28 and the approximate flow rate is a linear function, it is contemplated that the relation between power delivered to humidifier 28 and approximate flow rate may be any suitable function (e.g., nonlinear, polynomial, etc.).

[0052] Although the disclosed embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made to the embodiments without departing from their spirit and scope.

Claims

WHAT IS CLAIMED IS:

1. A method for controlling a heated humidifier comprising: determining an approximate flow rate of gas flow in a conduit in fluid communication with a heated humidifier; and controlling the power delivered to the heated humidifier based at least on the approximate flow rate.

2, A method according to Claim 1 , further comprising: determining whether the approximate flow rate is below a predetermined threshold flow rate; and controlling the power delivered to the heated humidifier based at least on the determination that the approximate flow rate is below the predetermined threshold flow rate.

3. A method according to Claim 2, further comprising controlling the power delivered to the heated humidifier as a function independent of the approximate flow rate in response to the determination that the approximate flow rate is not below the predetermined threshold flow rate.

4, A method according to Claim 1, wherein controlling the power delivered comprises: increasing the power delivered to the heated humidifier as the approximate flow rate increases; and decreasing the power delivered to the heated humidifier as the approximate flow rate decreases.

5. A method according to Claim 1, wherein controlling the power delivered comprises delivering power according to the following equations:

PD ^ PS for R_Λ> Rτ

Po - PsCnRM + m) for R_Λ < Rτ

where P_D is the power delivered to the heated humidifier, R_A is the approximate flow rate, R_τ is a predetermined flow rate threshold, P_s is the power delivered at flow rates not below the predetermined flow rate threshold, and n and m are constants.

6. A method according to Claim 1, wherein: the heated humidifier is an integral part of a breathing assistance system; and the gas is a breathable gas.

7. A method according to Claim 6, wherein the breathing assistance system is adapted to provide at least one of continuous positive airway pressure (CPAP), bi-level CPAP, and ventilation support to a patient.

8. A method according to Claim 1 , further comprising: measuring a temperature associated with the heated humidifier; and controlling the power delivered to the heated humidifier based at least on the measured temperature.

9. A method according to Claim 8, wherein controlling the power delivered to the heated humidifier further includes: delivering power to the heated humidifier in response to determining that the measured temperature is below a predetermined maximum temperature; and not delivering power to the heated humidifier in response to determining that the measured temperature is above the predetermined maximum temperature.

10. A breathing assistance system comprising: a gas delivery system operable to supply breathable gas; a patient interface configured to interface with a patient for delivering breathable gas to the patient; a connection system configured to communicate breathable gas supplied by the gas delivery system to the patient interface for delivery to the patient; a heated humidifier coupled to at least one of the patient interface and the connection system, and configured to humidify the breathable gas; and a control module configured to: determine an approximate flow rate of breathable gas in the breathing assistance system; and control an amount of power delivered to the heated humidifier based at least on the approximate flow rate.

11. A breathing assistance system according to Claim 10, further comprising a flow detector coupled to at least one of the gas delivery system, the patient interface, and the connection system, and operable to measure the approximate flow rate of breathable gas.

12. A breathing assistance system according to Claim 10, wherein the control module is configured to: determine whether the approximate flow rate is below a predetermined threshold flow rate; and control the power delivered to the heated humidifier based at least on a determination that the approximate rate is below the predetermined threshold flow rate.

13. A breathing assistance system according to Claim 11, wherein the control module is further configured to control the power delivered to the heated humidifier independently of the approximate flow rate in response to the determination that the approximate flow rate is not below the predetermined threshold flow rate.

14. A breathing assistance system according to Claim 10, the control module further configured to: increase the power delivered to the heated humidifier as the approximate flow rate increases; and decrease the power delivered to the heated humidifier as the approximate flow rate decreases.

15. A breathing assistance system according to Claim 10, the control module further configured to deliver power to the heated humidifier according to the following equations:

PD = PS for RA > RT

P_D = P_s(nR_M + m) for RA < RT

where P_D is the power delivered to the heated humidifier, R_A is the approximate flow rate, R_T is a predetermined flow rate threshold, Ps is the power delivered at flow rates not below the predetermined flow rate threshold, and n and m are constants.

16. A breathing assistance system according to Claim 10, wherein the breathing assistance system is adapted to provide at least one of continuous positive airway pressure (CPAP), bi-level CPAP, and ventilation support to a patient.

17. A breathing assistance system according to Claim 10, wherein the control module is further configured to: measure a temperature associated with the heated humidifier; and control the power delivered to the heated humidifier based at least on the measured temperature.

18. A method according to Claim 17, wherein the control module is further configured to: deliver power to the heated humidifier in response to a determination that the measured temperature is below a predetermined maximum temperature; and not deliver power to the heated humidifier in response to a determination that the measured temperature is above a predetermined maximum temperature.

19. A humidification system, comprising: a reservoir operable to contain a fluid and configured to interface with a conduit in fluid communication with the reservoir; and a heater coupled to the reservoir and configured to: heat the fluid to humidify a gas flowing through the conduit; and generate heat as a function of an approximate flow rate of the gas in the conduit.

20. A humidification system according to Claim 19, further comprising a flow detector operable to measure the approximate flow rate.

21. A humidification system according to Claim 19, further comprising a control module operable to: measure the approximate flow rate in the conduit; and control an amount of power delivered to the heater humidifier based at least on the approximate flow rate.

22. A humidification system according to Claim 19, wherein the heater is further configured to generate heat based on at least a temperature associated with the heated humidifier.

23. A humidification system according to Claim 22, wherein the heater is further configured to: generate heat when the temperature is below a predetermined maximum temperature; and not generate heat when the temperature is above the predetermined maximum temperature.

24. A system for controlling a heated humidifier comprising: a flow detector operable to measure a flow rate of a gas flowing in a conduit in fluid communication with a heated humidifier; and a control module coupled to the flow detector and configured to control the power delivered to the heated humidifier based at least on the measured flow rate.