WO2010027282A2

WO2010027282A2 - Contactless power transfer in a system for providing respiratory gases to a user for therapeutic purposes

Info

Publication number: WO2010027282A2
Application number: PCT/NZ2009/000187
Authority: WO
Inventors: Nordyn Alami; Aiguo Hu; Kai Sui Tnay; Hao Zheng; Su Ping Chin; Chin Fei Low
Original assignee: Fisher & Paykel Healthcare Limited
Priority date: 2008-09-05
Filing date: 2009-09-04
Publication date: 2010-03-11
Also published as: WO2010027282A3

Abstract

A respiratory system comprising a gas unit having a gases outlet and an integrated power supply, the gas unit supplying a stream of pressurised gases to a breathing conduit with first and second ends, and which has an integrated heater wire, the first end pneumatically coupled in use with the outlet, the gas unit also having an electrically isolated transmitter coupling at the outlet, the breathing conduit having an electrically isolated receiver coupling at the first end, the transmitter coupling and the integrated electrical power supply mutually adapted so that the transmitter coupling receives power from the power supply when the breathing conduit is pneumatically coupled to the outlet, the transmitter coupling and the second electrically isolated receiver coupling mutually adapted to form an electrically isolated mutual connection so that the transmitter coupling transmits power to the receiver coupling, and the heater wire receives operational power.

Description

"CONTACTLESS POWER TRANSFER IN A SYSTEM FOR PROVIDING RESPIRATORY GASES TO A USER FOR THERAPEUTIC PURPOSES"

FIELD OF THE INVENTION

The invention relates to power and data transfer in respiratory systems. More specifically, this invention relates to systems, or apparatus, or both, for transmission of electrical power, or communication signals, or both, between components of a respiratory system.

BACKGROUND OF THE INVENTION

Respiratory systems for the purposes of CPAP therapy or similar are configured to provide breathing gases to a user's respirator}' tract. In general, a respiratory system of this type comprises a source of breathing gases (e.g. a CPAP blower) pneumatically coupled to a user interface (e.g. a face mask, a nasal mask, a nasal cannula) by at least one gases conduit. Breathing gases are transferred from the gas source, through the conduit, to the user interface.

Some respiratory systems may also incorporate a humidifier to reduce dehumidifϊcation of the user's respiratory tract. The humidifier may be integrated with the gas source or incorporated in the respiratory system as a separate unit. Usually the humidifier is direcdy downstream from the oudet of the blower unit A common type of humidifier comprises a chamber adapted to hold a volume of water. In use, the water is heated by a chamber heater (commonly a plate heater adjacent to the humidifier chamber) to produce water vapour within the chamber. Breathing gases are directed through the chamber and become humidified as they pass through the water vapour in the chamber. The breathing gases are then delivered to the user via the delivery conduit and patient interface

The breathing gases may be heated further, or maintained at a temperature within the delivery conduit after they exit the humidifier chamber. Heating the breathing gases within the conduit helps to reduce condensation (rain out) and facilitates delivery of the breathing gases at a temperature or near to a temperature close to the users body temperature, with high moisture content (preferably the gases are saturated).

To ensure breathing gases are delivered to the user within the desired range of operating conditions, many modern respiratory systems incorporate a control system to regulate operating parameters. The control system may modulate parameters such as the chamber and conduit heater temperature and gas supply pressure and flow rate

It is generally preferable, and may be essential in some respiratory system designs, to provide feedback to the control system. Feedback control is generally considered more robust and accurate that open loop control. Feedback is provided to die control system with one or more sensors that measure properties of the breathing gases, user 01 both and relay the data to the control s) stem Based on the measurements received from the sensors, the control s) stem can adjust the control parameters to regulate the respiratory system output

As has been outlined above, respiratory systems provide heated humidified gases. In order to control the gases conditions (pressure, humidity, etc), a control system which receives data from sensors throughout the system is used. To accurately control the respirator}' system output (the breathing gases delivered to die user) it is desirable to measure the system output as precisely as possible. This requires positioning the sensors near to the breathing gases delivery point to ensure the measured parameters reflect the conditions experienced by the user. It can also be desirable to measure the conditions of the gases as the gases exit the humidifier or blower unit The sensors can be of the active type that require a power source. The sensors will also need a connection to the controller in order to relay measurements back to the controller. Electrical connections are usually made between metallic connectors or similar, which can corrode in high humidity atmospheres. It can also be desirable to repeatedly connect and disconnect various components in the breathing circuit, for example to connect a different type of interface, or to replace a conduit or interface. It is desirable that these connections can be made as reliably and repeatably as possible.

SUMMARY OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS Preferred forms of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a typical respirator}' humidifϊcation system. The system includes a gas source, a separate humidifier unit and a user interface, all pneumatically coupled by breathing conduits. The user interface incorporates a sensor which is coupled to the conduit heating wire by an electrically isolated power coupling.

Figure 2 is a close up schematic diagram of a respiratory system user interface which can be coupled to a breathing conduit heater wire by an inductive power coupling. The primary and secondary coils are depicted in association with the breathing conduit and user interface respectively The secondary circuit electronics and sensor are illustrated on the user interface. Figure 3 is a schematic diagram of a pneumatic adapter positioned between the user interface and breathing gas conduit. The adapter is configured to form an electrically isolated power coupling with the breathing conduit heater wire. Figure 4 is a schematic diagram of a respiratory system similar to that shown in Figure 1, incorporating two electrically isolated power couplings, one between the humidifier unit and a breathing conduit, and one between the same conduit and the user interface. The first coupling is between the humidifier and the breathing conduit heater wire. The second coupling is between the breathing conduit heater wire and the user interface.

Figure 5 is a block diagram of an inductive power coupling circuit suitable for use in a respiratory system. The circuit includes a free oscillation circuit for improved energy utilisation.

Figure 6 is a simplified block representation of a control algorithm for the inductive power coupling circuit illustrated in Figure 5 Figure 7 is a circuit diagram of a push-pull current fed resonant inverter configured to autonomously regulate primary induction coil excitation.

Figure 8 is a simplified circuit diagram of a capacitive power coupling incorporating a push-pull current fed resonant converter.

Figure 9 is a schematic representation of a capacitive power coupling structure. Figure 10 is a block diagram representation of a capacitive power coupling illustrating component inter-relations

Figure 11 is a block diagram representation of a respiratory system incorporating two electrically isolated power couplings An inductive coupling links a breathing conduit heater wire to a power source. A capacitive power coupling links the heater wire to a sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A respiratory system 100 for the deliver}' of breathing gases to a user is described below with reference to the Figures. In the system shown in the figures the breathing gases are heated, humidified and supplied to a user 1 at a pressure above atmospheric. The respiratory system 100 incorporates a sensing mechanism by which parameters of the breathing gases, respiratory system and/or user (such as temperature, pressure, gas flow rate, humidity and gas composition) can be measured at or close to the point at which the gases are delivered to the user 1.

The preferred form of the sensing mechanism is lightweight and small in size to accommodate use at the patient end of the respiratory system. Proficient sensor configuration reduces the discomfort experienced by the user by allowing the patient interface to be lighter and less cumbersome. A number of different types of sensors are known in the art which would be suitable for use in this manner. In the preferred embodiments, the sensor(s) are of the active type and require a power source. The invention as described below is suitable for both respirator) humidification (RH) and obstructive sleep apnea (OSA) treatment, and can be used with CPAP, BiPAP, APAP, or OpcnCPAP blower units, other variable flow, pressure and/or humidification units or similar respiratory devices. An exemplary respiratory humidification system is illustrated in Figure 1. A ventilator or blower unit 15 provides a source of breathing gases at a pressure above atmospheric. Preferably the blower unit 15 includes a variable speed fan 20 which can be manipulated to alter the delivery pressure or flow of breathing gases. In the pictured embodiment, the speed of fan 20 may be varied manually by a user, through user controls 19, or automatically by controller 18 Various gases, including oxygen, anaesthetic, or air can be supplied by blower unit 15.

A humidifier chamber 5 is located downstream of the blower unit 15, such that the humidifier chamber 5 receives gases from the blower unit 15 The humidifier chamber 5 may be integrated with the blower unit 15 (as commonly encountered in home use systems) or provided as a separate unit (as depicted in Figure 1), connected by a humidifier conduit 17 or another suitable gas passageway. The humidifier chamber 5 has an inlet 16 which is fluidly connected to the outlet of the blower unit. In use all or a substantial portion of the gases leaving the blower unit 15 are delivered to the humidifier chamber 5 via the inlet 16 In the preferred embodiment, the humidifier chamber 5 is a hollow plastic body with a metal base Preferably, the humidifier chamber 5 is sealed, apart from the provisions of an inlet 16 and an oudet 4. In use, the humidifier chamber 5 holds a volume of water 6 that is heated by a heater plate 7, the metal base of the humidifier chamber 5 contacting the heater plate 7 to facilitate heat transfer. In embodiments where the humidifier chamber is incorporated in the blower unit, the heater plate 7 is usually integrated into the blower unit 15, and the humidifier chamber 5 rigidly and releasably connected adjacent the heater plate. When the humidifier chamber 5 is heated, a portion of the water 6 evaporates creating a vapour within the chamber. The breathing gases entering the humidifier chamber 5 from the blower unit 15 mix with the water vapour, increasing the moisture content of the breathing gases. Accordingly, the gases exiting humidifier chamber 5 through outlet 4 are both heated and humidified before being delivered to the patient or user 1. Breathing conduit 3 fluidly connects the humidifier 5 to a patient or user interface 12. The inspirator₎' conduit 3 and patient interface 12 form a gases transportation pathway from the humidifier chamber 5 to the patient 1.

In the preferred embodiment, breathing gas conduit 3 incorporates a heater to reduce condensation ('rain out') and maintain the temperature of the breathing gases as they are transported to a patient 1. In the embodiment pictured in Figure 1 the conduit 3 is heated by a heater wire 11 which is helicall) or spiiall) wound in or aiound the conduit 3 The heater wiie 11 is electrically coupled to a connector 32 at the humidifier end of the conduit 3 In the pictured embodiment the conduit connector 32 is adapted to receive a complimentarily configured cable 14 The cable 14 provides an electrical pathway between humidifier unit 30 (through humidifier connector 13) and the heater wire 11

The patient interface depicted in Figure 1 is a full face mask engaged over the mouth and nose of the user 1 However, there exist a multitude of patient interfaces which can be combined with the respiratory system described above Compatible interfaces include nasal masks, oral masks, sealing and non-sealing nasal cannula and intubation interfaces which pass through the trachea, bypassing the patient's upper airways

Preferabl} the blower unit 15 or the humidifier 30 (or both) incorporate a controller, control system or contiol mechanism 9 In general, the control system 9 receives input from any user controls and sensors located in the respiratory system and alters or ad_justs corresponding system outputs accordingly (for example the speed of the fan 20, the temperature of the heater plate 7, etc) Preferably the controller 9 executes an algorithm stored in software or control circuitry that determines how to adjust the system parameters in response to the received inputs The control system ma) also display the system output parameters, measured gas properties, user ad_justed parameters and other information including codes and system diagnostics The controller 9 of the preferred embodiment is a microprocessor or logic circuit, which includes an associated memory oi storage mechanism that holds a software based algorithm The controller 9 is adapted to receive and process real-time data gathered by sensors located at various positions within the respirator_}' system Preferably, the control system 9 includes an interface for user interaction or user controls 10 as shown in Figure 1 When active, die respiratory system operates in accordance with the instructions embedded in the hardware and pre-programmed software, modulating the output parameters of various hardware components to obtain the desired control objectives For example, the speed of the blower fan 20 may be altered to adjust the pressure or flow witlun the respiratory system, the power supplied to heater plate 7 may be regulated to control the heat or humidity of the breathing gases exiting the humidifier chamber, and the power supplied to heater wire 11 ad_justed to regulate the heat or humidity of gases delivered to the patient 1

In the embodiment pictured in Figure 1 , a sensor (or multiple sensors) 18 are located in the patient interface 12 The sensor 18 preferably measuies properties of the breathing gases (such as flow rate, pressure, temperature, humidity, gas composition), providing measurements leflective of the gases state immediately pnoi to delivery Alternatively, a sensor may be positioned within the breathing conduit (preferably toward the usei end) or incorporated within a pneumatic connector introduced between the breathing conduit and other system components. This offers the potential of a 'retrofit' for older or non-compatible user interfaces

Inductive power coupling The blower unit 15 is usually plugged into a source of mains power The blower unit 15 or the humidifier 30 provide electrical power to the respirator}' system components Auxiliary cables are commonly employed to distribute electrical power and communication or measurement data to components positioned remote of the power supply The auxiliary cables are usually interfaced to the respective components with conventional contact connectors — that is, direct contact between conducting elements allows an electrical connection for power (or data) transfer.

An auxiliary cable connection is depicted in Figure 1 between the humidifier 30 and the breathing conduit heater wire 11. A conventional contact connector 32 couples the power supply cable 14 to the heater wire 11. The electrical power deliveied to the heater wire 11 is used to heat the deliver}' conduit 3 and provide operational power for the user interface sensor 18. The heater wire 11 and user interface circuitry are coupled by an electrically isolated power coupling located at interface junction 22. No direct electrical contact is made between the two halves or elements of the couple. The electrically isolated power coupling across interface junction 22 comprises a pair of inductively coupled coils in close proximity, with power transferred b} means of interlinked electromagnetic fields from each of the coils. Primary coil 2 is associated with the breathing conduit 3. Secondary coil 19 is associated with the user interface Both coils are preferably integrated into the connector parts that pneumaticall_} couple the user interface 12 and conduit 3. In the most preferred embodiment, each of the coils is sealed (for example in a solid plastic unit) so that moisture cannot get into the coil. In the most preferred embodiment, data can also be communicated between the sensor

18 and the controller 9 through the heater wire 11 and the electrically isolated coupling, preferably by superimposing the data signal with the power signal Alternatively, data can be transmitted wirelessly from the interface circuitry 31 to the controller 9 Wireless transmission is preferably facilitated by a network incorporating a transmitter located proximate the sensor 18 and a receiver located proximate the controller 9 Data transmission between the sensor 18 and controller 9 may include signals representative of the propeity or properties measured b} the sensor, component specific data such as a fault codes or a component identifier to ensure compatibility. The electricall) isolated powei coupling piovides power (and optionally data tiansfer) between two circuits that do not have a direct contact electrical connection The particular form of isolating coupling illustiated in Figures 1 to 6 is an inductive coupling The inductive coupling is established between a coil or set of primary coils 2 associated with the patient end of conduit 3 and a secondary coil or set of secondary coils 19 associated with the patient interface 12

In use, the primary coils 2 are subjected to an oscillating electric current which induces a changing magnetic field in the vicinity of the coils 2 The magnetic field oscillates with the same frequency as the current The strength of the induced magnetic field (B) is direcdy proportional to the number of turns (N₁) of the primary coils 2 and the instantaneous current (I) flowing through the coil 2, and reduces with distance (R) from the primary coils 2 The relationship defining the strength of induced magnetic field is presented in Equation 1 The physical pioperties are linked b\ the magnetic field constant μ₀ (referred to as the permeability of free space)

Equation 1 B = N,μ_υI/2R Where

B = Magnetic field strength (T)

R = Distance from primary coils (m)

I = Current (A) μ_n — permeability of free space (4π x 10⁷ Tm/A) N₁ — Number of primary coil turns

The magnetic field created by the current flowing through the primary coils 2 induces an electromagnetic force (EMF) in the secondary coils 19 by mutual induction The induced EMF is dependant on the magnetic flux (φ) and the number of turns (N₂) of secondary coils 19

Equation 2 EMF₂ = N₂ Δ (φ)/ Δ t Where

EMF₂ = EMF induced in the secondary coils (V) N₂ — Numbei of secondary coil turns Δ (φ) = Change in magnetic flux (Wb) Δ t = Change in time (s) The magnetic flux (φ) is a quantit) of the inductn e coupling and depends on the strength of the magnetic field (B) and the orientation of the primary and secondary coils. The magnetic flux relation is presented in Equation 3.

Equation 3: φ = ABcosθ Where: φ = Magnetic flux (Wb)

A = Surface area (m²)

B = Magnetic field strength (T)

Θ = Angle between magnetic field and surface (rad) The induced EMF in the secondary coil 19 is capable of diiving a current through the resistn e load provided by the user interface circuitry 31 and providing operational power for the remote electrical component, such as the sensor 18.

The patient interface 12 and associated circuitry are shown in Figure 2. The conduit 3 and patient interface 12 are pneumatically coupled by interlocking male/female connectors. The primary 2 and secondary 19 coils are shown co-located with the pneumatic connector parts. The illustrated connector configuration provides a concentric arrangement of the coils when engaged, with the secondary windings 19 enclosing the primary windings 2. However, the specific connector gender allocation does not significantly alter the inductive coupling performance, and is preferably selected to satisfy compatibility considerations Although the general connector configuration does not significantly alter the inductive coupling performance, it is preferable that the magnetic padiway between the primary coils 2 and secondary coils 19 is minimised to prevent excessive magnetic flux leakage and unnecessary inefficiencies. Also visible in Figure 2 is the secondary circuit or reception electronics 31 associated with the patient interface The reception electronics 31 control the reception and modulation of power in the secondary coils 19. For instance, the power received across the inductive junction is preferably passed through a regulator circuit before supply to the sensor 18. The regulator circuit ensures the sensor 18 receives a consistent power supply which is not disturbed by external noise A rectification circuit may also be incorporated with the reception electronics 31 to convert the AC power, inherently received in the secondary coils 19, into DC power if required The secondary circuit 31 may also include an energy buffer, such as a capacitor or a small rechargeable cell, to compensate for any inconsistencies in the power being supplied across the electrically isolated power coupling. An alternate user interface configuration is illustrated in Figure 3. The illustrated user interface 112 comprises a pair of nasal pillows that are inserted in the nares of the user. The interface 112 is configured to be lightweight and small in size. A pneumatic connector 150 couples the breathing gas conduit 103 and the patient interface 112. The pneumatic coupling 150 permits the associated sensor 118 to be positioned adjacent the breathing gas deliver}' point without being direcdy associated with the user interface 112. The pneumatic connector 150 incorporates the secondary coils 119 and a sensor 118, providing backward or retrofit compatibility with older style interfaces and allowing greater user selection. As the pneumatic connector 150 facilitates compatibilift with user interfaces that do not incorporate the desired sensor(s), the user interface can be configured exclusively for ergonomic comfort. Preferably the connector 150 is fabricated from a substantially rigid plastic and is of similar internal diameter to the breathing gas conduit. The connector 150 is configured to mechanically engage the patient end of breathing gas conduit 103 and the inlet of patient interface 112 to provide a substantially sealed pneumatic pathway between the components. The inductive power coupling can be formed substantially simultaneously with the pneumatic connection in both preferred interface embodiments (Figure 2 or 3).

As the inductive coupling between the respective respiratory system components depends only on the proximity of the primary and secondary coils (not a physical connection) the power connection does not suffer from mechanical degradation over it's lifetime of use. Additionally, as the power connection between the respirator}- system components does not utilise direct contact electrical connectors there is reduced potential for a user to connect incompatible components, or incorrectly connect compatible components. There is also reduced potential for incomplete or incorrect electrical connections to be made between components, for example if two connectors were only partially in contact as die result of an incorrecdy made connection. The interlocking magnetic fields from the coils make the connection more effectively.

An alternate respiratory system configuration is illustrated in Figure 4. The illustrated respiratory system incorporates two electrically isolated power coupling _junctions. The two _junctions are coupled in series to form a single transmission network acting between the powei source and the remotely located electrical components. Both junctions are depicted as inductive couplings.

The first inductive junction couples the humidifier and the deliver}' conduit heater wire 11. The second inductive junction couples the heater wire 11 and the user interface circuitry 31 Both junctions are preferably collocated with the respective pneumatic connectors as illustrated The humidifier end inductive coupling comprises a set of complementary induction coils. The humidifier end primary coils 200 are associated with the humidifier outlet 4 The humidifier end secondary coils 219 are associated with the breathing conduit 3 The humidifier end secondary coils 219 are electrically connected to patient end primary coils 2 by heater wire 11 which forms the second inductive coupling. Primary circuit configuration

Generally the primary coils of the inductive coupling aie excited with a changing current waveform of between approximately 20 kHz and 200 kHz

Preferably the coils are excited with a frequenc) of less than 150 kHz, as Electromagnetic Compatibility (EMC) spectrum analysis for medical products begins at this frequency. However, the EMC standard also considers harmonics derived from the primary waveform. For this reason, the preferred current waveform is sinusoidal as it minimises electromagnetic interference. Other waveforms, such as sawtooth, triangular or square are also anticipated, although the effects of the resonant harmonics may require further consideration. Unwanted harmonics can interfere with other electronic equipment and create inefficiencies within the electrical circuit. The frequency with which the primary coils are excited depends on the characteristics of the primary coils (in particular the reactance), the desired transmission frequency and the medium through which the magnetic field must permeate to reach the secondary coils. In the preferred embodiment power is transmitted through the conduit heater wire at a lower frequency than the transmission frequency across the inductive coupling Transmission of the power waveform at lower frequencies through the heater wire reduces reactive losses and EMI generation. In the preferred embodiment, the power waveform is transmitted through the heater wire at a frequency below 200 Hz (preferably 20 Hz), which coincides with the excitation frequency of the heater wire in regular use (the heating waveform frequency) Switching or frequency conversion electronics are preferably provided adjacent the patient end of the inspiratory conduit 3 to facilitate conversion of the low frequency heater waveform to an transmission frequency suitable for exciting the primary coils. The primary circuit switching electronics are situated between, and in electrical communication with, the supply cabling (preferably heater wire 11) and primary coils 2

In the preferred embodiment, the primary side electronics utilise an oscillator}' or resonant circuit to generate the current wavefoim required to establish the inductive power coupling. The oscillatory circuit is tuned to oscillate at the primary coil excitation frequency. A simplified block circuit diagram of the respiratory circuit electronics is provided in Figure 5 The respiratory system illustrated in Figure 5 draws power from a respiratory device 330 (commonly a blower or humidifier unit), which is powered by a connection to a mains circuit. Preferably the respiratory device 330 supplies a square power waveform with a 20 Hz period. The power phase or duty cycle of the supply waveform is controlled by pulse width modulation (PWM) according to the heating requirements of the respirator}' system. In the preferred embodiment the duty cycle of the waveform (the phase during which energy is available to be in_jected into the primary 370 circuit) is modulated between 10% and 90% of the total cycle duration. During the remainder of the supply waveform period (corresponding to the 'off period) no energy is supplied to the heating wire, or consequently the inductive coupling. Both the primary circuit 370 and secondary circuit 371 illustrated in Figure 5 incorporate various energy storage components to compensate for the fluctuant power supply available to the inductive junction The primary coils 302 are situated in an inductive circuit 361, which is electrically coupled to the respiratory device 330 by the heater wire 311 The heater wire 311 is situated in a heating circuit 360, which also incorporates a heating switch 351. The heating switch is preferably a semiconductor switch The heater wire 311 is separated into an inductive component (inductor 312) and a resistive component (resistor 313) in the illustrated circuit. The inductive circuit 361 is coupled in parallel to the heating circuit 360. A diode 315 is positioned between the heating circuit 360 and the free oscillation or free ringing circuit 304. The diode 315 acts as a half bridge rectifier and prevents the capacitor 320 from discharging back to the heating circuit 360.

The free ringing circuit 304 is located subsequent to diode 315, and comprises the capacitor 320 in conjunction with the primary coils 302. Induction switch 350 controls the supply of power to the induction circuit 361, and consequendy the power injected into the free ringing circuit 304. Similar to heating switch 351, induction switch 350 is also preferably a semiconductor switch

Resonant converter active control

Transmission of power across the inductive power transfer coupling may be regulated by a control algorithm, such as the algorithm represented in Figure 6. The algorithm 400 modulates the state or orientation of switches 350, 351 to inject energy into the resonant circuit 304.

Preferably the controller executing the control algorithm 400 is integrated with, or located adjacent to, the switching electronics. To compensate for fluctuations in the power waveform provided by the respiratory device 330 (particularly when the duty cycle of the PWM supply is low as a result of reduced heating requirements) an auxiliary power supply 349 may be required. The auxiliary power supply 349 provides a consistent operating power to the controller and switching electronics. Preferably the auxiliary power supply 349 is adapted to receive and store power from the respiratory device 330 during the power phase of the supply waveform. The stored energy is then dissipated to the controller and switching electronics during the remainder of the waveform cycle when direct power is unavailable

An example of a suitably configured auxiliary power suppl) circuit comprises a simple current limiting resistor and a zener diode situated in parallel with a capacitor. When the circuit 300 is initiated the control algorithm 400 enters a start up routine represented in Figure 6 by start block 403. Preferably the start up routine periodically alternates the orientation of switches 350 and 351 to introduce energy into resonant circuit 304 and establish an inductive coupling between the primary 319 and secondary 302 coils. The start up switching period preferably coincides with the resonant frequency of the free ringing circuit 304 to enable soft switching. Energy is in_jected into the resonant circuit 304 during the power or 'on' phase of the supply waveform. When the controller determines that an inductive coupling is established and the free ringing circuit 304 is adequately initialised (preferably triggered by feedback that sufficient energy has been injected into the LC resonant tank 304 or after a predetermined time has elapsed) the circuit transitions to steady state control In steady state operation the controller executes a feedback routine to regulate energy injection. The controller initialises energy injection to coincide with voltage zero crossings within the resonant tank 304 Energy is therefore only injected into the resonant circuit 304 when the stored energy, already present in the circuit 304, is in the appropriate phase of oscillation. This soft switching technique generally results in greater efficiency and reduced electromagnetic interference (EMI) when compared with conventional switching techniques (such as forced periodic switching) Energy injection into the resonant circuit 304 is facilitated in the control algorithm by activating output block 405 (corresponding to the induction switch 350) and deactivating output block 407 (corresponding to heating switch 351). This switch configuration electrically connects the induction circuit 361 to the respiratory device 330. Output block 405 is driven direcdy from the gating block 404. Conversely, output block 407 is driven with the inverse of the gating block 404 output (through inverter block 406). Switches 350 and 351 are therefore alternated to ensure that they are always of opposing orientation, providing two distinct states for respiratory system 300.

The first state is a heating configuration. In the heating state switch 351 is closed, bypassing the resonant tank 304. The second state is an energy replenishment configuration. In the second state switch 350 is closed and energy is injected into the resonant circuit 304. The heater wire 311 receives sufficient power to heat the transitioning breathing gases (maintaining the prescribed temperature and humidity) in both states. Preferably changes to circuit state (heating to energy injection) are controlled to coincide with the voltage zero crossing measured across the resonant circuit 304 capacitor 320 (the transition from a clockwise potential difference to a counter clockwise potential difference). Ciicuit state transition is implemented duiing the power phase of the supply wavefoim by monitoring the oscillating voltage across the plates of capacitor 320 (represented block 401 in Figure 6), comparing this measured voltage with a refeience voltage (comparator block 402) and controlling the state of switches 350, 351 (represented by output blocks 405, 407 respectively) through the gating block 404 The output of gating block 404 depends on the orientation of the instantaneous current flowing through the free ringing circuit 304, which is determined by the pieviously detected chaige orientation across capacitor 320 Energy is injected into the resonant circuit 304 when the detected voltage zero ciossing represents a transition from a positive (clockwise) driving voltage to a negative (counter clockwise) driving voltage Controlling energy injection to coincide with the counter clockwise transition ensures the in_jected energy supplements the stored energy oscillating within the circuit 304 Preferably the quantity of energy injected to replenish the resonant circuit 304 is determined by feedback from the secondary circuit 371 Feedback energy injection control can be facilitated by continuously monitoring the voltage acioss the secondar) circuit 371 output (load 318 as indicated in Figure 5) to determine input energy requirements

By monitoring the secondar)' circuit output the controller can compensate for variations in the secondary circuit 371 load by injecting additional energy into the LC resonant tank 304 during eneigy replenishment The energy injection process can therefore be controlled according to the energy requirements of die secondary circuit 371 load 318 To accommodate energy injection feedback control a signal representative of the instantaneous output voltage is transmitted to the controller Preferably the signal is transmitted wirelessly from the secondary circuit to a receiver associated with the switching electronics However, if the heater duty cycle is to be modulated the receiver may alternatively be associated with the respiratory device 330

An alternate to feedback energy injection control is periodic energy injection Periodic energy injection involves periodically injecting energy into the free ringing circuit 304 and storing any energy excesses in the secondar}' circuit 371 energy buffer 340 Periodic energy injection does not reflect the energy usage of the secondar)' circuit 371 load 318, and therefore requires greater amounts of energy to be injected and stored than feedback energy injection control

Resonant converter passive control An alternate switching ciicuit with passive switching control is illustrated in Figuie 7

The circuit 500 is a push pull inveiter incorporating a iesonant tank 504 with primary induction coils 502 The circuit 500 illustrated in Figuie 7 is configured to receive a DC supply power and could be incorporated into a respiratory blower or humidifier to inductively couple the respective unit to a breathing conduit heater wire The circuit could also be modified to receive a fluctuating power supply, such as the low frequency PWM waveform used to excite the breathing conduit heater wire.

A DC power source 530 provides electrical energy to the push-pull inverter 500. A DC inductor 580 is coupled with the power source 530 to form a quasi-current source 590. The quasi-current source 590 is coupled to a phase splitting transformer 560, which divides the supplied current and allows energy to be efficiently injected into the resonant tank 504 during both oscillation phases. The phase splitting transformer is comprised of two identical inductors 561, 562. It is feasible to replace the physical DC inductor 580 with the leakage inductance generated by the splitting inductors 561, 562. Switching is facilitated by a pair of semi-conductor switches 571, 572. One terminal of each switch 571, 572 is coupled to ground. The other terminal is maintained at the potential experienced at a respective end (lnlet/oudet depending on current orientation) of the resonant circuit. The switches 571, 572 are driven by the voltage experienced at the other respective end of the resonant tank 504 so that they are always of alternate state (one switch is on and the other is off). Gate resistors 573, 574 protect the switches 571, 572 from voltage spikes. The resonant frequency of the resonant tank 504 determines the switching frequency of the inverter 500, as the state of the switches 571, 572 alternate with the resonant tank 504 oscillation phase. The circuit 500 is also able to adapt to load changes (such as heater wire loading) which alter the resonant tank 504 resonant frequency, as the switches 571, 572 are driven at the resonant tank 504 voltage zero crossings. An attractive attribute of the inverter circuit 500 is that both the power and signals required to drive the semiconductor switches 571, 572 are provided by the voltage across the mam circuit, allowing the circuit 500 to operate autonomously of external control.

Resonant circuit operation

When the circuit is in the energy replenishment state (induction switch 350 closed), electrical energy from the power supply is injected into the free ringing circuit or LC resonant tank 304. The injected energy is then temporarily stored in the resonant circuit 304, oscillating between magnetic potential energy, in the form of the induced magnetic field surrounding the primary coils 302, and electrical potential energy, stored as a charge differential across the plates of the capacitor 320 The circuit oscillations result from an interaction of the energy storage mechanisms of the primary coils 302, acting as an inductor, and the capacitor 320

In the energy injection phase energy is stored in both the capacitor 320 and the primary coils 302. When the respirator}' system 300 transitions into the heating state (induction switch 350 is opened) the capacitor 320 begins to discharge, maintaining a clockwise current through free ringing circuit 304. The discharged energy is transferred, and subsequently stored, in the magnetic field surrounding primar_\ coils 302 Eventually, when the current flowing through the free ringing circuit 304 reduces, the magnetic field begins to collapse and induce an electromagnetic force (EMF) in the primary coils 302. The energy extracted from the magnetic field, in the form of the induced EMF, opposes the change in current and results in the capacitor 320 becoming charged with a potential difference of reverse polarity. Once the collapsing magnetic field is depleted the process is reversed, with the capacitor driving a counter clockwise current through the iesonant tank 304.

The frequency at which the stored energy oscillates within the free ringing circuit 304 corresponds to the circuit resonant frequency. The correlation between the circuit components and the resonant frequency can be approximated by the relationship in Equation 4.

Equation 4: ω - V(I /LC) Where ω = The circuit resonant frequency (Hz)

L = The circuit inductance (h) C = The circuit capacitance (F)

The primary coils are excited at the free ringing circuit 304 resonant frequency, which also represents the power transmission frequency across the electrically inductive coupling. The energy stored in the LC resonant tank 304 gradually dissipates, with the majority of the dissipated energy being transmitted across the inductive power _junction to secondary circuit 371. Additional energy is injected into the resonant tank circuit 304 at voltage zero crossings to replenish the dissipated energy and supplement the stored energy.

The circuit oscillations provide a substantially sinusoidal waveform across the primary coils 302. When the power supply enters the 'off period, the stored energy in the resonant circuit 304 is gradually depleted before the subsequent duty cycle begins. As energy from the power supply is only available intermittendy the received energy must be buffered to provide a continuous supply the control reception electronics either side of the junction. A tuning capacitor 335 is illustrated in series widi die secondary coils 319. The tuning capacitor is intended to improve the transmission frequency of the inductive coupling by matching the secondary circuit resonant frequency with the coupling transmission frequency. Effective 'tuning' can produce in a resonant inductive coupling with greater power reception in the secondary coils The waveform transmitted across the inductive power _junction has essential!₎ the same alternating frequency as the oscillating waveform produced in the LC resonant tank 304. The receπ ed alternating waveform is consequently converted to a direct current (DC) suppl) , suitable for charging the energy storage buffer 340 and supplying the secondary circuit load 318, by a full bridge rectifier 333.

Power transmission across the inductive power coupling is fundamentally constrained by the duty cycle of the PWM waveform. As the duty cycle of the primary power supply is modulated to reflect the heating requirements of the deliver}' conduit, the power available to the resonant circuit 304 can vary sigmficandy. To accommodate for fluctuations in the received power supply, the secondary circuit incorporates a regulator 332. The regulator, preferably linear or switched mode, reacts to variations in the received power and stabilises the power supplied to the energy storage buffer 340 and the secondary circuit load 318. The energ} buffer 340 is preferably a super capacitor or small rechargeable cell. The buffer 340 stores electrical energy (in the form of electrical charge) during the 'power' phase of the primary circuit waveform. The stored buffer energy is gradually discharged to the secondary circuit load 318 as the free ringing circuit 304 oscillating energy (and consequently the energ} available for transmitted across die electrically isolated power coupling) is depleted. The energy storage buffer 340 stabilises the power available to the secondary load 318 by at least partially compensating for the fluctuations of the primary power supply. Capacitive power coupling

Capacitive coupling represents the transfer of energy within an electrical network by capacitance between circuit nodes. A capacitive coupling is formed when an electric charge created within a first conductor causes an adjacent conductor to hold an electric charge of opposite polarity. The formation of charge in the second conductor results from the influence of an electric field generated by the charge distribution in the first conductor.

Capacitive power coupling is another form of electrically isolated power coupling. The notable differences between capacitive power coupling and inductive power coupling are:

1. Capacitive coupling is facilitated b} an electric field,

2 Capacitive couplings require a higher excitation fiequency (kHz - MHz), 3. Generally capacitive couplings radiate less EMI as the electric field is confined between the coupling structures,

4. Capacitive couplings are generally more efficient as the coupling electric field is confined, 5. Capacitive coupling requires at least two coupling structure pairs to provide a completed current loop,

6. Capacitive couplings operate on the potential difference created between the coupling structures and do not have the same current requirements as inductive couplings, and

7 Capacitive couplings opeiate over smaller displacements (air gap) than inductive couples and are particularly suited to static applications.

A capacitive power coupling circuit diagram is presented in Figure 8. The circuit 600 incorporates a push-pull current fed resonant converter similar to the circuit 500 represented in Figure 7. A pair of capacitive coupling structures 691, 692 are disposed in parallel with the resonant tank 604. The oscillating voltage waveform created in the resonant circuit 604 is replicated in the primar) structure of each coupling structure 691, 692, causing the formation of an oscillating electric field. The electric field couples trie primary and secondary sides of the coupling structures 691, 692, driving a current through trie secondary circuit 631 A tuning inductor 635 is incorporated into the secondary circuit 631 to improve the coupling transmission efficiency. The tuning inductor 635 is selected to 'tune' the secondary circuit 631 resonant frequency to the coupling transmission frequency. The load on the secondary circuit is represented by resistance 618, and may correspond to the conduit heater wire, sensor or other electrical devices. The equivalent capacitance of each coupling structure can be expressed as:

Equation 5 : C = A E₀ S₁ / d Where:

C = Equivalent capacitance of each coupling structure (F)

A = Coupling area (m²) d — Distance between coupling structures (m) ε_r = Relative permittivity of the dielectric ε,, = Permittivity in a vacuum (8.85 x 10 ¹²)

A preferred form of coupling structure is illustrated in Figure 9. The coupling stiucture comprises two pairs of concentric cylinders The cylinder pairs 791, 792 are separated along their longitudinal axis. Each cylinder pair 791, 792 comprises an inner cylinder 711, 721 and an outer cylinder 710, 720 respectively. The inner cylinders 711, 721 are coupled to the secondary circuit and the outer cylinders 710, 720 are coupled to the primary circuit in the configuration illustrated in Figure 9. The coupling configuration illustrated in Figure 9 is desirable as the inner and outer

C₎ linders can be disposed on male and female pneumatic connector parts respectively. This provides manufacturing advantages and allows the pneumatic and electric coupling to be established simultaneously. Furthermore, the cylinder structure provides an enhanced coupling area (A) that can be configured with minimal coupling separation (d) to increase the transmission efficiency (as defined by Equation 5).

A block diagram representation of capacitively coupled primary 801 and secondary 802 circuits is presented in Figure 10. A power source 830

electrical energy to the circuit 800. The power source may provide DC (such as a blower or humidifier power supply) or fluctuating waveform power (such as a PWM heating waveform) The power is generally supplied at a frequency less than the coupling excitation frequency. A power converter 804 receives power from the power source 830 and modulates the power waveform for excitation of a capacitive coupling 890. Preferably the power converter 804 transforms the supply power to a excitation frequency above 100 kHz. A capacitive coupling 890 links the primary 801 and secondary 802 circuits. The capacitive coupling 890 compiises at least two coupling structure pairs. The primary structure of each coupling structure pair is excited with the waveform generated by the power converter 804, creating an oscillating electric field between the coupling structure pairs. The secondary structure of each capacitive coupling pair is coupled to a rectifier 833. The rectifier converts the alternating waveform received across the capacitive coupling to a DC waveform suitable for supplying the secondary electronics A compensator 835 is interjected between the capacitive coupling 890 and the rectifier 833 The compensator 835, preferably a tuning inductor, regulates the reception circuit characteristics The tuning capacitor can be arranged in series or parallel depending on the power level needed.

To accommodate fluctuations in the received power waveform, a voltage regulator 832 is coupled to the output of the rectifier 833. An energy buffer 840, such as a capacitor or a small rechargeable cell, is incorporated into the secondary cncuit 802 to compensate for any inconsistencies in the power being supplied across the electrically isolated power coupling. The regulator (preferably linear or switched mode) reacts to variations in the received voltage waveform and stabilises the power supplied to the energy storage buffer 840 and the secondary circuit load 818. The secondary load 818 receives a DC supply of operational power from the eneigy buffer 840. The load 818 may represent a sensor or sensor network located within the respirator} system. Alternatively, the load 818 may represent the heater wire and incorporate a suitable converter to produce the necessary heating waveform.

A specific

circuit power transmission system is illustrated in Figure 11. The system incorporates an inductive coupling between a respiratory unit (conventionally a blower or humidifier unit) and the respirator}' conduit 911. A second electrically isolated power coupling capacitively couples the respiratory conduit 911 and user interface. A DC power supply 930 provides a source of electrical energy to the respirator_}' circuit transmission system 900. The power source 930 is preferabl} integrated with either the respiratory unit or the humidifier unit. A push-pull converter 904 is also preferably co-located with the power source 930 The push-pull converter receives DC power from the power supply 930 and generates an excitation waveform suitable for dnving the primar_j coils 921 of the inductive coupling 919 The primary coils 921 and secondary coils 922 are preferably situated in or ad_jacent to the respective pneumatic connectors so that a pneumatic and electrical coupling between the conduit 911 and blower/humidifier can occur simultaneously. The inductive coupling 919 electrically couples the respirator) unit to the respiratory conduit heater wire 911. A tuning capacitor 935 is incorporated in the reception circuit to increase the inductive coupling transmission efficiency

A converter may optionally be incorporated adjacent the secondary coils 922 to convert the received power waveform to a suitable waveform for heating and transmission through the conduit 911 heating wire. Preferabl_} the heating waveform has a lower frequency than the inductive coupling 919 excitation waveform to reduce EMI.

The respiratory conduit heater wire is coupled to the user interface by a capacitive coupling 990. The capacitive coupling 990 may incorporate a converter (to generate a suitable excitation frequency from the heating waveform) or processing electronics (to regulate the excitation waveform if the heating waveform drives the capacitive coupling direcdy or is superimposed with an excitation waveform). The capacitive coupling comprises a pair of coupling structures 941, 942 that link the conduit circuit 901 to the interface circuit 902. A tuning capacitor 936 is allocated ad_jacent the capacitive coupling on the secondary side The tuning capacitor 936 regulates the reception circuit characteristics. The power received across the capacitive coupling is modulated into an acceptable format by a rectifier 933 and regulator 932 before delivery to the sensor 918. The data generated by the sensor 918 (both communication and measuiements) can be communicated back to die respiratory controller through the electrically isolated power coupling (superimposed with the power waveform) or across a wireless communication network.

Claims

1. A respiratory system comprising: a gas source unit having a gases outlet and an integrated electrical power supply, and adapted to supply a stream of gases from said oudet at a pressure above atmospheric, a breathing conduit having a first end and a second end and configured to pneumatically couple at said first end with said oudet to receive said stream of gases, said breathing conduit having an integrated heater wire adapted to provide heat to said stream of gases within said conduit in use, said gas source unit further having a first electrically isolated transmitter coupling associated with said oudet, said breathing conduit further having a second electricall₎ isolated receiver coupling associated with said first end, said first electrically isolated transmitter coupling and said integiated electrical power supply mutually adapted so that said first electrically isolated transmitter coupling receives power from said integrated electrical power supply, in use, with said breathing conduit pneumatically coupled to said oudet, said first electrically isolated transmitter coupling and said second electrically isolated receiver coupling mutually adapted to form an electrically isolated mutual connection so that said first electrically isolated transmitter coupling transmits power to said second electrically isolated receiver coupling, said heater wire configured to receive operational power from said second electrically isolated receiver coupling.

2. A respiratory system as claimed in claim 1 wherein said first electrically isolated transmitter coupling and said second electrically isolated receiver coupling are induction coils, said gas source unit further having a resonant circuit configured to in use oscillate at a frequency corresponding to an excitation frequency of said induction coils.

3. A respiratory system as claimed in claim 2 wherein said gas source unit further has an autonomous switching circuit adapted to inject energy into said resonant circuit at voltage zero crossings.

4. A respirator_}' system as claimed in claim 1 wherein said first electrically isolated transmitter coupling and said second electrically isolated receiver coupling are capacitive couplings, said gas source unit further having a resonant circuit configured to oscillate at a frequency corresponding to an excitation frequency of said capacitive couplings.

5. A respirator₎" system as claimed in claim 4 wherein said gas source unit further has an autonomous switching circuit adapted to inject energy into said resonant circuit at voltage zero crossings.

6. A respiratoiy system as claimed any of the preceding claims wherein said system further comprises a user interface, said second end of said breathing conduit and said user interface adapted to pneumatically connect so that gases from said gas source unit can pass through said conduit into said interface for deliver₎' to a user, said user interface further having a gases property sensor located and adapted to sense a property of said gases stieam at or close to the point of delivery to a user, said second end of said breathing conduit further having a first electrically isolated interface coupling, said user interface further having a second electrically isolated interface coupling, in use, widi said breathing conduit pneumatically coupled to said interface, said first electrically isolated interface coupling and said second electrically isolated interface coupling mutually adapted to form an electrically isolated mutual connection so that said first electrically isolated interface coupling transmits power to said second electrically isolated interface coupling, said sensor configured to receive operational power from said second electrically isolated interface coupling.

7. A respirator₎' system as claimed in claim 6 wherein said first electπcall₎ isolated interface coupling and said second electrically isolated interface coupling are induction coils, said respirator₎' system furthei having an interface resonant circuit configured to in use oscillate at a frequency corresponding to an excitation frequency of said induction coils.

8. A respiratory system as claimed in claim 7 wheiein said inspiratory s) stem further has an autonomous switching circuit adapted to inject energy into said interface resonant circuit at voltage zero crossings.

9. A respiratory system as claimed in claim 6 wherein said first electrically isolated interface coupling and said second electrically isolated interface coupling are capacitive couplings, said respirator}' system further having an interface resonant circuit configured to in use oscillate at a frequency corresponding to an excitation frequency of said induction coils.

10. A respiratory system as claimed in claim 9 wherein said respiratory system further has an autonomous switching circuit adapted to inject energy into said resonant circuit at voltage zero crossings.

11. A respiratory system as claimed in claim 6 wherein said respiratory system further has a controller integrated in said gas source unit, and said heater wire, said first electrically isolated interface coupling and said second electrically isolated interface coupling are further configured to provide a pathway for transmission of data from said gases propert₎ sensor to said controller, said data superimposed over a power waveform in said heater wire.

12. A respiratory system as claimed in claim 6 wherein said respiratory system further has a controller integrated in said gas source unit, and data from said sensor is wirelessly transmitted to said controller.

13. A respiratory system as claimed in any one of the preceding claims wherein any or all of said electrically isolated couplings are configured so that simultaneous electrical couplings and pneumatic couplings are made in use.

14. A gas source unit for use as part of a respirator}' breathing circuit comprising: a casing having a gases mlet and a gases outlet, an integrated electrical power supply contained within said casing, adapted to receive power from a mains source and provide power to components in said respirator}' breathing circuit, a controllei located within said casing and adapted to receive inputs from user controls and sensors in said respiratory system, a fan unit located in said casing, said fan unit adapted to receive a stream of gases from said gases inlet and supply a stream of gases to said oudet at a pressure above atmospheric, said oudet adapted to in use pneumatically couple to a breathing conduit to supply said stream of gases to said breathing conduit, said gas souice unit further having an electrically isolated transmitter coupling associated with said oudet, in use, with said breathing conduit pneumatically coupled to said oudet, said first electricall} isolated transmitter coupling adapted to transmit power to a second electrically isolated receiver coupling

15. A gas source unit as claimed in claim 14 wherein said first electrically isolated transmitter coupling is an induction coil

16 A gas source unit as claimed in claim 15 wherein said controller has a resonant circuit configured to in use oscillate at a frequency corresponding to an excitation frequenc} of said induction coil.

17. A gas source unit as claimed in claim 16 wherein said controller further has an autonomous switching circuit adapted to inject energy into said resonant circuit at voltage zero crossings.

18 A gas source unit as claimed in claim 14 wherein said first electrically isolated transmitter coupling is a capacitive coupling

19 A gas source unit as claimed in claim 18 wherein said controller has a resonant circuit configured to in use oscillate at a frequency corresponding to an excitation frequency of said capacitive coupling.

20 A gas source unit as claimed in claim 19 wherein said controller further has an autonomous switching circuit adapted to inject energ) into said resonant circuit at voltage zero crossings.

21. A user interface for use as part of a respirator) breathing circuit comprising; a gases receiving portion adapted to pneumaticall) connect to a gases conduit in use and receive a stream of gases at a pressure above atmospheric, a gases delivery portion adapted to receive said stream of gases from said gases receiving portion and deliver these to the airway of a user in use, said user interface further having a gases property sensor located and adapted so as to sense a property of said gases stream at or close to the point of delivery to a user, said user interface further having a electrically isolated interface coupling, in use, with said breathing conduit pneumatically coupled to said interface, said electrically isolated interface coupling adapted to receive transmitted power, said sensor further configured to receive said transmitted power via said electrically isolated interface.

22. A respiratory system as claimed in claim 21 wherein said electrically isolated interface coupling is an induction coil.

23. A respiratory system as claimed in claim 21 wherein said electrically isolated interface coupling is a capacitive coupling

24. A respiratory system as claimed in any one of claims 21 to 23 wherein said electrically isolated interface coupling is further configured to provide a pathway for transmission of data from said gases property sensor, said data superimposed over the transmitted power wavefoim from said electrically isolated interface coupling to said sensor.

25. A breathing conduit for use as part of a respirator}' breathing circuit comprising; a flexible self-supporting sealed pathway having a first open end and a second open end, said first end configured to pneumatically couple to a gases source to receive a pressurised stream of gases in use, said second end adapted to pneumatically couple to a patient interface in use to deliver said stream of gases to a user, an integrated heater wire in said sealed padiway, arranged between said first and second ends and adapted to provide heat to said stream of gases within said conduit in use, a first electricall) isolated receiver coupling associated with said first end, a second electrically isolated transmitter coupling associated with said second end, said first electrically isolated receiver coupling adapted to receive power from an electrical power supply in use, said first electrically isolated receiver coupling adapted to onwardl) transmit power in use, said first electrically isolated transmitter coupling providing operational power to said heater wire.

26. A breathing conduit as claimed in claim 25 wherein said first and second electricall₎ isolated couplings are configured so that simultaneous electrical couplings and pneumatic couplings are made in use.

27. A breathing conduit as claimed in claim 25 or claim 26 wherein at least one of said electrically isolated couplings is an induction coil.

28. A breathing conduit as claimed in claim 25 or claim 26 wherein at least one of said electrically isolated couplings is a capacitive coupling.

29. A breathing conduit as claimed in any one of claims 25 to 28 wherein said heater wire is further adapted to provide a pathway for transmission of data.