Patent ID: 12220529

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred and alternative forms of the breathing assistance apparatus of the present invention are described below.

FIGS.1aand1bshow a schematic view of a breathing assistance apparatus, and a user1receiving a stream of gases at a pressure above atmospheric from the breathing assistance apparatus by way of a patient interface. The breathing assistance apparatus is generally made up of a blower unit2, a humidifier unit3, a conduit4and a patient interface.

The blower unit2in the embodiment has an internal fan unit6. Air from atmosphere enters the blower unit2via an inlet and is pressurised by the fan unit to a pressure above atmospheric. The flow of gases provided by the fan unit6then exits the blower unit2via blower outlet7, and enters the humidifier unit3. The stream of gases is heated and humidified as it passes across the surface of water8contained in the humidifier unit3. The heated, humidified, pressurised gases stream then exits the humidifier unit3via the humidifier outlet9, and enters the conduit4, which is connected by a first end to the humidifier outlet9. The gases pass along the conduit4to the user or patient1and are delivered to the user1via the patient interface, which is connected to the second end or patient end of the conduit4.

Other sources of breathing gases at a controlled pressure and/or flow are also within the scope of the invention. For example the gases source may be from a compressed gases reservoir or a central high pressure supply with pressure and/or flow controlled by one or more regulators.

In the embodiment shown inFIG.1a, the patient interface is a nasal cannula5. In the embodiment shown, the nasal cannula5is a side-entry cannula, with the conduit extending to one side of the nasal cannula5. However, the cannula could be any type of nasal cannula well-known in the art. In the alternative embodiment shown inFIG.1b, the patient interface is a nasal mask10, of the type that is well-known in the art.

In each of the breathing assistance apparatus described above, the apparatus includes a humidifier unit3. It should be noted that the invention could be reduced to practice using a breathing assistance apparatus which does not include a humidifier unit. Furthermore, in the embodiment ofFIGS.1aand1b, the blower unit2and the humidifier unit3are shown as separate items, remotely located from one another, and connected by an intermediate conduit11. A combined or integrated blower/humidifier unit could be used, where the humidifier unit and blower unit are co-located in use and connected so as to effectively form a single item. It should also be noted that a nasal cannula and a nasal mask have been shown and described, but a full-face mask or nasal pillows could be used instead of the nasal mask shown inFIG.1b.

In this specification, the general term ‘gases supply unit’ will be used to refer to either a blower unit by itself, supplying gases to a connected conduit via the blower outlet7, or to a blower unit and humidifier unit in combination, with gases supplied to the connected conduit via the humidifier outlet9.

The blower unit2also contains a control unit13. Control unit13is adapted to send signals to elements in the breathing assistance apparatus to change their output. For example, the control unit13controls the speed of the fan that forms part of the fan unit6. The speed of the fan determines the pressure (and therefore flow) provided by the breathing assistance apparatus. In this embodiment the control unit can also control other items such as, for example, a heater plate14which forms part of the humidifier unit3in some variations, or a heater wire15which is located in the conduit4in some embodiments. When providing normal closed CPAP therapy, the fan will typically be operated by the control unit13at a substantially constant speed in order to provide a stream or flow of gases at a substantially constant pressure above atmospheric. However, other techniques involving active control (where the control unit adjusts the fan speed relative to a patient's breathing pattern) may also be used. Such techniques often involve the control unit slowing the fan speed as a patient exhales, and increasing the fan speed to provide a suitable CPAP pressure as they inhale. Furthermore, the control unit may control the speed of the fan according to a feedback control based on data of a parameter of the flow, typically pressure.

The control unit may be a multipurpose micro computer with stored or embedded software executing a control program. Alternatively the controller may be a single purpose micro computer or programmed logic processor such as an FPGA. Alternatively the controller and algorithm may be implemented in fixed logic circuits.

In the preferred embodiments of the present invention, the breathing assistance apparatus also has user controls16providing input to the control unit13, which the user1or a health professional can use to alter the outputs of the breathing assistance apparatus. For example, a health professional will prescribe a therapy regime that will require a user to receive gases at a certain pressure during their sleep. The user controls16can be used to set the pressure of the gases delivered by the blower. The controller13receives the input from the user controls16and sets the fan speed accordingly in order to deliver the required pressure. The user controls16may be a simple discrete selection switch to indicate a mode of operation, or a more complex user interface that allows a user to adjust operation parameters stored in the control such as fan speed, output pressure and flow rate. In addition, the user may also be allowed to adjust data concerning the preferred humidity and delivery temperature of the supplied gases within certain limits.

In some embodiments of the present invention, the breathing assistance apparatus has a flow sensor12. The flow sensor12may be built into the patient interface (e.g. the nasal cannula, the nasal mask, the full-face mask or the nasal pillows). Alternatively, the flow sensor12may be located at or close to the blower outlet or anywhere in the gases flow path in the blower. Signals representative of the flow rate are fed back to the controller as data of the sensed flow.

The apparatus of the present invention may also include a pressure sensor to measure the gas pressure supplied to a patient. The pressure sensor may be located at the output of the fan unit6or at the patient interface5,10. The controller can deduce the pressure at the patient interface5,10by estimating the pressure drop in the conduit4. The pressure sensor outputs a signal to the controller unit13the control unit13may use this data of the pressure to control the speed of the fan6.

As has been outlined above, the breathing assistance apparatus can be used with a number of different types of interface. For normal CPAP operation, the operating parameters required for effective therapy may vary with the type of interface which a user prefers or has recommended to them. The pressure can be adjusted manually via the user controls16to set a required pressure. The controller13will control the fan unit6to provide the selected pressure. However, when different types of interface, or conduit, or both in combination are connected to the blower unit, the gases flow rate through the interface will be different depending on the specific conduit or interface which is connected.

CPAP therapy is the most common form of treatment that is initiated when a patient is diagnosed for obstructive sleep apnea-hypopnea syndrome (OSAHS). However, studies have shown that many patients are non-adherent to CPAP treatment. Non-adherence to treatment can be attributed to mask-related issues including pressure or airflow related issues and problems related to nasal delivery. Non-adherence to treatment may also be related to headgear issues including the headgear being too tight or cumbersome, or to inconvenience of masks, or to spousal intolerance.

Traditional PAP therapy methods involve a nominally sealed mask. The mask seals to the face of the user, but typically a fixed or variable leak outlet is provided in the mask body or in a close portion of the supply conduit. An alternative is high-flow therapy (HFT). HFT is being used in clinical settings and is being applied across a range of age groups and varieties of disease conditions. The high flow rates of HFT are typically delivered via an open nasal cannula interface system. For HFT, humidification of the breathing gases is important. Preferably the supplied inspiratory gases are warmed to body temperature and humidified to at least 70% saturation. In contrast, CPAP devices tend to deliver gases at a relatively lower temperature. For CPAP, the temperature is typically limited to around 32 degrees so as to not exceed skin surface temperature, which may cause discomfort to the patient. However, that notwithstanding, an HFT device may allow the user some control over the temperature of the delivered gases to increase comfort. Properly conditioned gases provide for patient comfort and minimize deterioration of nasopharyngeal structures. HFT is sometimes referred to as humidified high-flow nasal cannula (HHFNC) therapy. For the purpose of this specification, traditional CPAP therapy will be referred to as “closed CPAP” and high flow therapy will be referred to as “open CPAP”.

The patient interfaces intended to provide closed CPAP therapy (e.g. interfaces intended to seal against the face of a user, such as a nasal mask, a full-face mask, or nasal pillows) will have a different flow rate profile than a nasal cannula providing ‘open’ CPAP therapy. Open CPAP therapy does not require the nasal cannula to seal against the nostrils of a user. The present invention recognises that there are characteristic differences in the flow profiles between interfaces which are intended to provide sealed or closed CPAP therapy and interfaces which are intended to provide unsealed or open CPAP therapy. A system which uses an unsealed interface instead of a sealing interface may also use a conduit of a different internal diameter to connect between the static units (e.g the blower and humidifier) and the user interface. Where reference is made in this specification to an interface, this can mean any one of the following: a mask (full-face or nasal) by itself, a nasal cannula interface by itself, or either of the preceding examples with a gases supply conduit also connected. We also use the term supply path to refer to the combination of the patient interface with the gases supply conduit.

Open CPAP treatment or treatment with nasal insufflation or ‘trans nasal insufflation’ (TNI) is based on the principles of HFT where an open nasal cannula system is used to deliver high flow rates to the nares of a patient to alleviate the symptoms of obstructive sleep apnoea-hypopnea syndrome (OSAHS) or upper airway resistance syndrome (UARS). It has been shown in the art that a linear increase in expiratory pharyngeal pressures (EPP) is possible with increasing flow rates. For example, EPP increased from 0.8-7.4 cmH2O during mouth closed and from 0.3-2.7 cmH2O during mouth open, for flow rates from 0-60 L/min.

The preferred embodiment of the present invention is a single blower unit, optionally combined with a humidification unit, to be capable of delivering both closed CPAP (which operates to achieve or deliver a prescribed pressure) and open CPAP therapy (which operates to achieve or deliver a prescribed flow). Furthermore, the preferred embodiment of the present invention has a pressure and flow generator that has the ability to detect the type of interface (CPAP mask or open CPAP nasal cannula) connected at the end of the breathing circuit. Subsequent to this detection the controller may adjust the operating parameters or automatically switch between CPAP and open CPAP delivery modes depending on the interface detected at the end of the breathing circuit.

According to an aspect of the present invention, determination of the supply path is made from measured characteristics of the gases flow. However, in less preferred embodiments applicable to other aspects of the invention, determination may be made based on other physical characteristics of the supply path or based on specific identification characteristics of the supply path. For example, the controller may determine the supply path based on the electrical resistance of an included heater wire; or the controller may determine the supply path by sensing an identity from contacts on the conduit connector or by interrogating an included RFID tag.

Open CPAP treatment promotes adherence to the treatment regime due to the nasal cannula being more comfortable for a user. Physicians may also choose to first prescribe open CPAP therapy to a patient sensitive to comfort issues with closed CPAP therapy. The physician may choose to switch the patient to closed CPAP treatment when the patient is comfortable with open CPAP treatment. A patient may also wish to use open CPAP for part of the night before switching to traditional CPAP therapy for the remainder of the night, or vice versa. This approach could be preferred due to the relative comfort provided by open CPAP over traditional CPAP and hence the patients may find it easier to fall asleep on the open CPAP system. Switching CPAP treatment regimes would normally require the use of separate open and closed CPAP systems which will involve a high cost.

Further, the pressure demands of OSAHS patients may change over time and a physician may find that the pressure requirements for a patient initially prescribed CPAP therapy have altered over time and that they can be successfully treated with open CPAP. Similarly, a patient initially prescribed open CPAP may require higher pressures and require a CPAP device. Again, switching devices will involve a high cost and may therefore be prohibitively expensive.

In some circumstances, the blower unit2(and humidifier unit3) may be re-used with another user, or a user may change from closed or sealed therapy to open or unsealed therapy. A different combination of conduit and interface may be connected to the blower/humidifier in order to provide a stream of pressurised gases to a user.

As has been outlined in relation to the prior art, several ways or methods have been suggested in which the blower unit can adjust the output in response to having a new or different item or items connected to it. All of these methods rely on a component to provide a physical identification—for example, a unique connector, a resistor having a known value, or an RFID tag which is associated with the component and which contains data which allows the system to adjust to an appropriate output.

In contrast, one aspect of the present invention uses the physical characteristics of the supply path itself to determine the type of connected interface. For example, the controller may examine the flow rate which a particular interface type and conduit type in combination exhibits when connected to a particular blower unit with the fan running at a particular speed in order to produce a set output pressure. In the preferred embodiment of the invention the controller of the blower unit senses the flow characteristics of the interface to which the blower unit is connected, determines what the interface is from the flow and pressure characteristics and automatically switches or adjusts the output according to predetermined flow characteristics that best suit the connected interface. The flow and pressure characteristics of the connected breathing tube and patient interface are thereby sensed by the sensor and this date is used by the controller to determine the appropriate flow and pressure for CPAP therapy.

The sequence essentially taken by the preferred blower controller is to read the pressure/flow signal from the sensor. It will then calculate (a) long-term average value of the flow and (b) the flow/pressure fluctuation of the signal over some time period. The inventors have found the combination of (a) and (b) unique to the interface and conduit type connected to the blower. The controller uses this information to predict the interface and conduit type.

The algorithm does not need to operate only when the interface is not worn. Using characteristics (a) and (b) the control algorithm is able to predict the interface and conduit type in other scenarios (i.e., interface worn, not worn, blower ON or OFF etc.). This increases the robustness of the algorithm as the user does not have to wait for a certain time period for the control algorithm to determine what type of interface is connected. Therefore, the automatic detection and switching process can be completely transparent to the user.

When a supply path is not connected to the output of a blower unit, the pressure sensor reading will typically read close to atmospheric pressure. Similarly, a flow sensor (if one is present on the blower unit itself) may read a relatively high flow rate, for a given fan speed, when there is no interface connected which would otherwise provide a flow restriction. When a supply path is connected to the output of the blower unit, the increased resistance to flow will cause the pressure sensor to typically read at a higher pressure. Similarly, the flow sensor may read a flow rate below that expected for an unrestricted fan.

An open CPAP interface, as shown inFIGS.3and4, typically consists of a high resistance circuit whereas closed CPAP, as shown inFIG.2, typically utilizes a low resistance circuit. This is due to the characteristic nature of the open CPAP nasal cannula which has a much smaller internal cross-sectional area than a closed CPAP delivery tube and mask combination. For example, an open CPAP interface has approximately a 78 mm2cross-sectional area through which gases can pass, compared to a closed CPAP interface having approximately a 380 mm2cross-sectional area.

The smaller cross-sectional area of the open CPAP interface poses a higher resistance to flow. For a given driving pressure, and when the interface is not being worn by a user, an open CPAP interface fitted with a nasal cannula delivers a lower flow rate than a closed CPAP interface fitted with a mask. For example, at a set pressure of 6 cmH2O, an open CPAP system delivers a total flow rate of approximately 45 L/min of leak flow (with a Fisher & Paykel Healthcare 400502 large nasal cannula) compared to a flow rate of approximately 74 L/min of leak flow for a closed CPAP system utilizing a Fisher & Paykel Healthcare FlexiFit 407 NIV interface mask. The total flow rate through the system is one characteristic that can be used to determine whether an open CPAP interface or a closed CPAP interface is connected to the blower unit.

Another characteristic feature that the controller may use to detect whether an open CPAP interface or a closed CPAP interface is connected to the blower unit is the difference between the pressure fluctuation and flow fluctuation that occurs during the inspiration-expiration cycle (IEC). A small fluctuation of approximately 15-20 L/min at a set pressure of 6 cmH2O can be observed during the IEC when an open CPAP interface is being used. The flow fluctuation, or swing, can be attributed to the non-sealing nature of the open CPAP interface cannula which does not attempt to maintain a constant pressure at the nares. In contrast, there is a much larger flow fluctuation of approximately 50-60 L/min at a set pressure of approximately 6 cmH2O when a closed CPAP mask is used. This is due to the tight seal around the mask which maintains the delivered pressure. If the mask seal is compromised and air leaks occur, the IEC flow fluctuation decreases with increasing leak. The controller can use this relationship to differentiate between a reduction in flow fluctuation due to mask leak and the reduction in flow fluctuation due to the use of an open CPAP nasal cannula. The total system flow rate is much lower for an open CPAP system than for a closed CPAP system with a leaky mask.

The controller could alternatively use pressure fluctuation. If the controller is operating in a flow controlled mode, which can be a useful mode for delivering open CPAP, the controller can look at the fluctuations in the output of a pressure sensor in communication with the gas supply path, or at fluctuations in the power applied to the blower motor. An open CPAP nasal cannula will exhibit smaller fluctuations than the closed CPAP interface.

The controller may initiate a test mode51when it detects an interface has been connected to the output of the blower unit. The test mode51is illustrated in more detail inFIG.6. In the first step53the controller operates the blower with the interface connected and samples data related to the gases flow.

At step54the controller analyses the flow and pressure data at each of the fan speeds. Alternatively, the second step may be to analyse either the flow or the pressure data. For example, when a patient interface connection with the blower unit is detected, the pressure data may be immediately indicative of what sort of interface is connected. As noted above, an open CPAP interface typically has a small diameter conduit connecting the interface to the blower unit. Using the data from the pressure sensor the controller means immediately determine that an open CPAP interface is connected if the controller determines that the data indicates an increase in pressure that corresponds to having a small conduit connected to the output of the controller unit. Alternatively the blower may examine the average flow and pressure signals or fluctuations in the flow signal.

At step55the controller compares (at56) the flow and pressure sensor data to a set of stored values. Typically the different types of patient interfaces will exhibit different flow and pressure values across one or more fan speeds. If the measured data does not fit any stored profile information, the controller may repeat steps53to55or the controller may revert to the detection mode50. This circumstance may indicate that the user has not properly connected a new patient interface, or has connected the interface, but is not yet wearing the mask. Alternatively, where the controller finds a match, or substantial alignment of measured and stored data, the controller will set the operation mode52of the blower unit to control the fan speed according to the type of connected interface, or set a mode of operation according to the type of interface determined by the algorithm.

Referring again toFIG.5, controller will change or alter the operation mode52according to the type of interface that has been determined by the control strategy. For example, the controller will typically set the operating mode for closed CPAP therapy to deliver a pressure range of 4 to 20 cmH2O, which will typically see flow rates of up to or exceeding 40 L/minute. However, the controller may be configured to set an operational flow rate range, instead of a pressure range. In another example, the controller will typically be configured to set the operating mode for open CPAP therapy to deliver flow rates of 20 to 40 L/minute, which will typically require a pressure range of approximately 4-6 cmH2O. However, the controller may be configured to set an operational pressure range, instead of a flow rate range. The controller may be configured to set the fan speed according to the pressure and/or air flow requirements, as dictated by the operation mode best suited to the detected interface.

In the preferred embodiment of the invention the controller of the blower unit will switch between two operating modes according to the detected interface. Switching between the two delivery modes will primarily entail delivering either (a) a fixed (or controlled) pressure (or alternatively automatically titrating the pressure depending on patient needs) when the device is in ‘closed CPAP’ mode or (b) a fixed (or controlled) air flow rate (or automatically titrating the flow rate to suit patient needs) when in ‘open CPAP’ mode. Preferably, when a closed CPAP interface is determined as being connected, the controller controls the output of the blower to provide a substantially fixed or controlled pressure. Additionally, when an open CPAP interface is determined as being connected, the controller controls the output of the blower unit to provide a substantially fixed or controlled gases flow rate.

The controller may be programmed to periodically run a check, at step57, to ensure the system is behaving as expected. The check may include, for example, comparing the current speed of the fan against an expected range of pressure and flow readings. If the range falls outside predetermined limits, the controller may then revert to the detection mode50to reassess the connected interface. The controller may further include a counter to monitor the number of occasions the limits are exceeded, and revert only after the limits are exceeded numerous times. This may account for momentary abnormalities in the system.

The controller is preferably configured to increase the supplied humidity, for example by commanding an increase in power to the humidifier heater plate, when switching from closed CPAP to open CPAP mode. This ensures the relatively high flow rates needed for open CPAP are adequately humidified. Similarly, the humidity is preferably decreased by the controller when switching from open CPAP to closed CPAP modes. The controller is preferably configured to increase the temperature of the delivered gases when switching from closed CPAP to open CPAP. For example, the controller can command an increase in the power to a heater in the supply path. The patient can tolerate a higher gases temperature in gases supplied direct to the nares than to a face mask. Similarly, the temperature is preferably decreased in switching from closed CPAP to open CPAP modes. If the controller can make a more detailed conclusion on mask type and distinguish different closed CPAP interfaces then this temperature response may be made according to determinations between direct nasal interfaces and mask type interfaces rather than between open CPAP and closed CPAP.

The general profiles of the most commonly used types of interface are, in the preferred embodiment, pre-loaded into the memory of the controller13. When an interface assembly (a conduit and an interface—e.g. conduit4and nasal mask10) is connected to the rest of the breathing assistance apparatus, the controller controls the blower unit2to provide a gases flow along the interface assembly, and the flow sensor12provides a reading to the control unit13. The control unit13recognises the type of interface which is being used, based on company the received sensor data to the stored flow profiles, and can generate an appropriate output accordingly. A user or health professional can, if necessary make manual adjustments to this profile to optimise the therapy. These adjustments can also be saved in the memory of the controller as the optimal values to which it should switch on detection of an interface type—they can replace the default values if necessary.

The memory of the controller13may be a removable device, such as a flash memory, static ram or CD-ROM, and interface by serial connection or similar protocols. The memory device may be purchased separately or together with a new type of patient interface and preferably a memory device containing flow and pressure information will be provided with a newly purchased patient interface. Alternatively, a connection between the controller and a remote facility can be made by wired or wireless communication to facilitate manual adjustments or upgrades from a remote location. For example, an internet connection or mobile communications system may be established to remotely connect the control system blower unit to a remote upgrade facility. The user interface on the blower unit may facilitate communication between local or remote data and control sources.

Further functions of the controller include recording information relevant to the machine usage and therapy. For example, the controller also preferably facilitates detection and recordal of ‘sleep disordered breathing’ events. Such events include apnoeas, hypopnoeas, respiratory effort related arousals, flow limitations and ‘wake from sleep’ events. The controller may be configured to record the time, date and duration of such events The controller may also record the time, date and duration that each of the treatment types or modes is operated for, or statistically informative information such as maximums, minimums, average, median, and mode values of pressure and gases flow rate readings. Another function of the controller is the calculation and recording of an efficacy parameter, such as the apnoea-hypopnoea index (AHI) or respiratory disturbance index (RDI). According to one invention herein the controller records data to identify the determined supply path as part of the efficacy and compliance data.

Calculation of an efficacy parameter may require the use of more sensitive flow or pressure sensing devices than are commonly used for generally sensing properties of the gases output from the blower unit. In such cases, a secondary flow or pressure sensing device may be provided with fluid connection to the breathing gases. The controller may switch the secondary sensor into the breathing circuit, or at least actively begin to monitor the secondary sensor in a manner that ensures normal operation of concurrent functions of the blower unit.

The controller may adjust or substitute the algorithms used for determining occurrence of events according to the determined supply path.

All of the calculated and recorded data in the controller is preferably stored on a removable media storage device. Alternatively, the data could be stored in fixed memory and downloaded to a separate memory device or remote server by an appropriate communications connection. The recorded data can also be used by a physician or other professional institution to determine whether a patient has undertaken sufficient therapy.

Providing the capability for a pressure/flow generator to automatically switch between open CPAP and CPAP delivery modes depending on the interface connected at the end of the delivery tube will provide a new approach for physicians to introduce OSAHS patients to traditional CPAP therapy via the use of an open CPAP system on a temporary basis. A large proportion of patients diagnosed with OSAHS refuse CPAP therapy at the outset due to mask and pressure related issues with CPAP therapy. However, open CPAP allows a physician to help a patient adapt to CPAP therapy via the open CPAP system, and it is generally a much more comfortable system for a patient new to CPAP therapy. The system will enable the patient to spend a proportion of each night on open CPAP and gradually transition to conventional CPAP therapy once they are able to tolerate CPAP. In addition, the combined open/closed CPAP system will be more flexible and allow the physician to change prescribed delivery modes without the purchase of additional pressure/flow generators.

Changing the mode of operation of the CPAP machine may be restricted by consideration of conditional elements. Such elements may include whether a treatment regime has been administered for a prescribed amount of time, or whether a calculated efficacy parameter indicates the mode can be changed. Other conditional parameters include the input of a unique code or identifier that effectively ‘unlocks’ previously unavailable functions. The status of such a conditional parameter can be communicated to a user by a graphical indication on the interface of the blower unit.

The ability of the device to automatically detect the interface connected at the end of the breathing tube and change the delivery mode appropriately will also remove the burden of manually changing the delivery mode from closed to open CPAP and vice versa using a manual method such as pressing a button on the pressure/flow generator. Relying on the patient to press the appropriate button has an additional disadvantage of being subject to errors made by the patient in selecting the appropriate delivery mode. In addition, having the ability for the device to automatically switch to the appropriate delivery mode depending on the interface connected to the breathing tube also makes the system easier to use for the patient.

Existing blower units that do not support automatic switching of flow profiles often have the capability for the controller software, or firmware, to be changed or updated. It is envisaged that exiting blower units can be updated to support automatic flow profile switching, including steps necessary to detect the type of interface connected to the blower unit by sensing flow data. Further, it is envisaged the software or firmware updates are facilitated by connection to a remote resource, such as a database. A connection can be made by wired or wireless communication. For example, an internet connection or mobile communications system may be established to remotely connect the control system blower unit to a remote upgrade facility.