Patent Description:
The airways include a series of branching tubes, which become narrower, shorter and more numerous as they penetrate deeper into the lung. The prime function of the lung is gas exchange, allowing oxygen to move from the inhaled air into the venous blood and carbon dioxide to move in the opposite direction. The trachea divides into right and left main bronchi, which further divide eventually into terminal bronchioles. The bronchi make up the conducting airways, and do not take part in gas exchange. Further divisions of the airways lead to the respiratory bronchioles, and eventually to the alveoli. The alveolated region of the lung is where the gas exchange takes place, and is referred to as the respiratory zone. See "<NPL>.

Examples of respiratory disorders include Obstructive Sleep Apnea (OSA), Cheyne-Stokes Respiration (CSR), respiratory insufficiency, Obesity Hyperventilation Syndrome (OHS), Chronic Obstructive Pulmonary Disease (COPD), Neuromuscular Disease (NMD) and Chest wall disorders.

Obstructive Sleep Apnea (OSA), a form of Sleep Disordered Breathing (SDB), is characterised by events including occlusion or obstruction of the upper air passage during sleep. It results from a combination of an abnormally small upper airway and the normal loss of muscle tone in the region of the tongue, soft palate and posterior oropharyngeal wall during sleep. The condition causes the affected patient to stop breathing for periods typically of <NUM> to <NUM> seconds in duration, sometimes <NUM> to <NUM> times per night. It often causes excessive daytime somnolence, and it may cause cardiovascular disease and brain damage. The syndrome is a common disorder, particularly in middle aged overweight males, although a person affected may have no awareness of the problem. See <CIT>).

Cheyne-Stokes Respiration (CSR) is another form of sleep disordered breathing. CSR is a disorder of a patient's respiratory controller in which there are rhythmic alternating periods of waxing and waning ventilation known as CSR cycles. CSR is characterised by repetitive de-oxygenation and re-oxygenation of the arterial blood. It is possible that CSR is harmful because of the repetitive hypoxia. In some patients CSR is associated with repetitive arousal from sleep, which causes severe sleep disruption, increased sympathetic activity, and increased afterload. See <CIT>).

Respiratory failure is an umbrella term for respiratory disorders in which the lungs are unable to inspire sufficient oxygen or exhale sufficient CO<NUM> to meet the patient's needs. Respiratory failure may encompass some or all of the following disorders.

A patient with respiratory insufficiency (a form of respiratory failure) may experience abnormal shortness of breath on exercise.

Obesity Hyperventilation Syndrome (OHS) is defined as the combination of severe obesity and awake chronic hypercapnia, in the absence of other known causes for hypoventilation. Symptoms include dyspnea, morning headache and excessive daytime sleepiness.

Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a group of lower airway diseases that have certain characteristics in common. These include increased resistance to air movement, extended expiratory phase of respiration, and loss of the normal elasticity of the lung. Examples of COPD are emphysema and chronic bronchitis. COPD is caused by chronic tobacco smoking (primary risk factor), occupational exposures, air pollution and genetic factors. Symptoms include: dyspnea on exertion, chronic cough and sputum production.

Neuromuscular Disease (NMD) is a broad term that encompasses many diseases and ailments that impair the functioning of the muscles either directly via intrinsic muscle pathology, or indirectly via nerve pathology. Some NMD patients are characterised by progressive muscular impairment leading to loss of ambulation, being wheelchair-bound, swallowing difficulties, respiratory muscle weakness and, eventually, death from respiratory failure. Neuromuscular disorders can be divided into rapidly progressive and slowly progressive: (i) Rapidly progressive disorders: Characterised by muscle impairment that worsens over months and results in death within a few years (e.g. Amyotrophic lateral sclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers); (ii) Variable or slowly progressive disorders: Characterised by muscle impairment that worsens over years and only mildly reduces life expectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic muscular dystrophy). Symptoms of respiratory failure in NMD include: increasing generalised weakness, dysphagia, dyspnea on exertion and at rest, fatigue, sleepiness, morning headache, and difficulties with concentration and mood changes.

Chest wall disorders are a group of thoracic deformities that result in inefficient coupling between the respiratory muscles and the thoracic cage. The disorders are usually characterised by a restrictive defect and share the potential of long term hypercapnic respiratory failure. Scoliosis and/or kyphoscoliosis may cause severe respiratory failure. Symptoms of respiratory failure include: dyspnea on exertion, peripheral oedema, orthopnea, repeated chest infections, morning headaches, fatigue, poor sleep quality and loss of appetite.

A range of therapies have been used to treat or ameliorate such conditions. Furthermore, otherwise healthy individuals may take advantage of such therapies to prevent respiratory disorders from arising. However, these have a number of shortcomings.

Various therapies, such as Continuous Positive Airway Pressure (CPAP) therapy, Non-invasive ventilation (NIV) and Invasive ventilation (IV) have been used to treat one or more of the above respiratory disorders.

Continuous Positive Airway Pressure (CPAP) therapy has been used to treat Obstructive Sleep Apnea (OSA). The mechanism of action is that continuous positive airway pressure acts as a pneumatic splint and may prevent upper airway occlusion, such as by pushing the soft palate and tongue forward and away from the posterior oropharyngeal wall. Treatment of OSA by CPAP therapy may be voluntary, and hence patients may elect not to comply with therapy if they find devices used to provide such therapy one or more of: uncomfortable, difficult to use, expensive and aesthetically unappealing.

Non-invasive ventilation (NIV) provides ventilatory support to a patient through the upper airways to assist the patient breathing and/or maintain adequate oxygen levels in the body by doing some or all of the work of breathing. The ventilatory support is provided via a non-invasive patient interface. NIV has been used to treat CSR and respiratory failure, in forms such as OHS, COPD, NMD and Chest Wall disorders.

Invasive ventilation (IV) provides ventilatory support to patients that are no longer able to effectively breathe themselves and may be provided using a tracheostomy tube.

In some forms, the comfort and effectiveness of these therapies may be improved.

These therapies may be provided by a treatment system or device. Such systems and devices may also be used to screen, diagnose, or monitor a condition without treating it.

A treatment system may comprise a Respiratory Pressure Therapy Device (RPT device), an air circuit, a humidifier, a patient interface, and data management.

A respiratory pressure therapy (RPT) device may be used individually or as part of a system to deliver one or more of a number of therapies described above, such as by operating the device to generate a flow of air for delivery to an interface to the airways. The flow of air may be pressurised. RPT devices typically comprise a pressure generator, such as a motor-driven blower or a compressed gas reservoir, and are configured to supply a flow of air to the airway of a patient. In some cases, the flow of air may be supplied to the airway of the patient at positive pressure. The outlet of the RPT device is connected via an air circuit to a patient interface such as those described below.

One known RPT device used for treating sleep disordered breathing is the S9 Sleep Therapy System, manufactured by ResMed Limited. Another example of an RPT device is a ventilator. The ResMed Elisée™ <NUM> ventilator and ResMed VS III™ ventilator may provide support for invasive and non-invasive dependent ventilation suitable for adult or paediatric patients for treating a number of conditions. These ventilators provide volumetric and barometric ventilation modes with a single or double limb circuit. <CIT> discloses an apparatus for treating a respiratory disorder configured to compute a measure of typical recent ventilation such that a rate of adjustment of the measure of typical recent ventilation is reduced as a measure of recent uncompensated leak increases and an apparatus for treating a respiratory disorder configured to compute a target ventilation from a product of a measure of typical recent ventilation and a target fraction, wherein the target fraction is dependent on the recent pressure support. <CIT> discloses a treatment system which applies a gain to a flow rate of pressurized gas delivered to a patient during inspiratory and/or expiratory phases of a respiratory cycle to deliver the pressurized gas in proportion to the respective gains during inspiration and/or expiration. Different gains may be selected for the inspiratory and expiratory phases of a respiratory cycle to minimize breathing work. <CIT> discloses an apparatus which determines the instantaneous phase in the respiratory cycle, average respiration rate and the provision of ventilatory assistance. A microprocessor receives an airflow signal from a pressure transducer and the microprocessor controls a servo that controls the fan motor. <CIT> discloses a breathing device having a respiratory gas source for generating a gas pressure for a patient, a measuring unit for measuring a measurement quantity characteristic of inhalation or exhalation, and a control unit which determines the patient's tidal volume from the measurement quantity and compares this with a setpoint value of the tidal volume. The control unit regulates the respiratory gas source such that the generated gas pressure is made available until the setpoint value of the tidal volume is reached.

A patient interface may be used to interface respiratory equipment to its wearer, for example by providing a flow of air to an entrance to the airways. The flow of air may be provided via a mask to the nose and/or mouth, a tube to the mouth or a tracheostomy tube to the trachea of a patient. Depending upon the therapy to be applied, the patient interface may form a seal, e.g., with a region of the patient's face, to facilitate the delivery of gas at a pressure at sufficient variance with ambient pressure to effect therapy, e.g., at a positive pressure of about <NUM> cmH<NUM>O relative to ambient pressure. For other forms of therapy, such as the delivery of oxygen, the patient interface may not include a seal sufficient to facilitate delivery to the airways of a supply of gas at a positive pressure of about <NUM> cmH<NUM>O.

Delivery of a flow of air without humidification may cause drying of airways. The use of a humidifier with an RPT device and the patient interface produces humidified gas that minimizes drying of the nasal mucosa and increases patient airway comfort. In addition in cooler climates, warm air applied generally to the face area in and about the patient interface is more comfortable than cold air.

There may be clinical reasons to obtain data to determine whether the patient prescribed with respiratory therapy has been "compliant", e.g. that the patient has used their RPT device according to one or more "compliance rules". One example of a compliance rule for CPAP therapy is that a patient, in order to be deemed compliant, is required to use the RPT device for at least four hours a night for at least <NUM> of <NUM> consecutive days. In order to determine a patient's compliance, a provider of the RPT device, such as a health care provider, may manually obtain data describing the patient's therapy using the RPT device, calculate the usage over a predetermined time period, and compare with the compliance rule. Once the health care provider has determined that the patient has used their RPT device according to the compliance rule, the health care provider may notify a third party that the patient is compliant.

There may be other aspects of a patient's therapy that would benefit from communication of therapy data to a third party or external system.

Some forms of treatment systems may include a vent to allow the washout of exhaled carbon dioxide. The vent may allow a flow of gas from an interior space of a patient interface, e.g., the plenum chamber, to an exterior of the patient interface, e.g., to ambient.

The present technology is directed towards providing medical devices used in the screening, diagnosis, monitoring, amelioration, treatment, or prevention of respiratory disorders having one or more of improved comfort, cost, efficacy, ease of use and manufacturability.

A first aspect of the present technology relates to apparatus used in the screening, diagnosis, monitoring, amelioration, treatment or prevention of a respiratory disorder.

Another aspect of the present technology relates to methods used in the screening, diagnosis, monitoring, amelioration, treatment or prevention of a respiratory disorder.

One form of the present technology comprises apparatus for treatment of a respiratory disorder using a safety volume servo-ventilation mode, in which the gain of the servo-control of pressure support is based on a differential between estimated inspiratory and expiratory volumes.

According to one aspect of the present technology, there is provided apparatus for treating a respiratory disorder in a patient. The apparatus comprises a pressure generator configured to generate a flow of air so as to provide ventilatory support to the patient; a transducer configured to generate a signal representing a property of the flow of air; and a controller configured to analyse the signal to estimate an inspiratory volume and an expiratory volume of a breath of the patient and servo-control the degree of ventilatory support to adjust an estimated tidal volume toward a target tidal volume. A gain of the servo-control is dependent on a difference between the estimated inspiratory volume and the estimated expiratory volume.

In an example of this aspect, the gain decreases as the difference between the estimated inspiratory volume and the estimated expiratory volume increases. In a further example, the gain is dependent on the difference between the estimated inspiratory volume and the estimated expiratory volume relative to the estimated tidal volume. Further still, the gain is dependent on the absolute magnitude of the difference between the estimated inspiratory volume and the estimated expiratory volume.

In another example of this aspect, the degree of the ventilatory support is a pressure support of the ventilatory support.

According to a further aspect of the present technology, there is provided a method of operating a respiratory treatment apparatus configured to generate a flow of air so as to provide ventilatory support to a patient. The method comprises measuring a property of the flow of air, using a transducer; analysing, in a controller, the measured property to estimate the inspiratory volume and the expiratory volume of a breath of the patient; calculating, in a controller, a gain dependent on a difference between the estimated inspiratory volume and the estimated expiratory volume; and servo-controlling, by a controller, the respiratory treatment apparatus using the calculated gain to adjust an estimated tidal volume for the patient toward a target tidal volume.

In an example of this aspect, the gain is dependent on the difference between the estimated inspiratory volume and the estimated expiratory volume relative to the estimated tidal volume. In other examples, the gain is dependent on the absolute magnitude of the difference between the estimated inspiratory volume and the estimated expiratory volume. In other examples, the degree of the ventilatory support is a pressure support of the ventilatory support.

According to a further aspect of the present technology, there is provided a system for treating a respiratory disorder in a patient. The system comprises means for generating a flow of air so as to provide ventilatory support to the patient; means for generating a signal representing a property of the flow of air; means for analysing the signal to estimate the inspiratory volume and the expiratory volume of a breath of the patient; and means for servo-controlling the degree of ventilatory support to adjust an estimated tidal volume toward a target tidal volume. A gain of the servo-control is dependent on a difference between the estimated inspiratory volume and the estimated expiratory volume.

According to a further aspect of the present technology, an apparatus for treating a respiratory disorder in a patient is provided. The apparatus comprises a blower configured to deliver a supply of air that provides ventilatory support to the patient; a transducer configured to generate a signal representing a property of the supply of air; and a controller. The controller is configured to analyse the signal to estimate an inspiratory volume and an expiratory volume of a breath of the patient; and adjust servo-control gain based on a difference between the estimated inspiratory volume and the estimated expiratory volume.

In an example of this aspect, the controller adjusts the servo-control gain so that the gain decreases as the difference between the estimated inspiratory volume and the estimated expiratory volume increases. In another example, an adjustment in servo-control gain causes a reduction in a rate of adjustment of pressure support of the supply of air. In other examples, the controller is configured to adjust the servo-control gain when the difference is greater than or equal to <NUM>%, or further configured to adjust the servo-control gain to a default value when the difference returns to a value that is less than <NUM>%.

The methods, systems, devices and apparatus described may be implemented so as to improve the functionality of a processor, such as a processor of a specific purpose computer, respiratory monitor and/or a respiratory therapy apparatus. Moreover, the described methods, systems, devices and apparatus can provide improvements in the technological field of automated management, monitoring and/or treatment of respiratory conditions, including, for example, sleep disordered breathing.

Also, various ones of the sub-aspects, aspects and/or example may be combined in various manners and also constitute additional aspects or sub-aspects of the present technology.

The following description is provided in relation to various examples which may share one or more common characteristics and/or features. It is to be understood that one or more features of any one example may be combinable with one or more features of another example or other examples. In addition, any single feature or combination of features in any of the examples may constitute a further example.

In one form, the present technology comprises an apparatus or device for treating a respiratory disorder. The apparatus or device may comprise an RPT device <NUM> for supplying pressurised air to the patient <NUM> via an air circuit <NUM> to a patient interface <NUM>, as shown for example in <FIG>.

A non-invasive patient interface <NUM> in accordance with one aspect of the present technology comprises the following functional aspects: a seal-forming structure <NUM>, a plenum chamber <NUM>, a positioning and stabilising structure <NUM>, a vent <NUM>, one form of connection port <NUM> for connection to air circuit <NUM>, and a forehead support <NUM>, such as depicted for example in <FIG>. In some forms a functional aspect may be provided by one or more physical components. In some forms, one physical component may provide one or more functional aspects. In use the seal-forming structure <NUM> is arranged to surround an entrance to the airways of the patient so as to facilitate the supply of air at positive pressure to the airways.

An RPT device <NUM> in accordance with one aspect of the present technology comprises mechanical, pneumatic, and/or electrical components and is configured to execute one or more algorithms <NUM>, such as any of the methods, in whole or in part, described herein. The RPT device <NUM> may be configured to generate a flow of air for delivery to a patient's airways, such as to treat one or more of the respiratory conditions described elsewhere in the present document. <FIG> provide illustrative examples of the components or schematics that may comprise RPT device <NUM>.

The RPT device may have an external housing <NUM>, formed in two parts, an upper portion <NUM> and a lower portion <NUM>. Furthermore, the external housing <NUM> may include one or more panel(s) <NUM>. The RPT device <NUM> comprises a chassis <NUM> that supports one or more internal components of the RPT device <NUM>. The RPT device <NUM> may include a handle <NUM>.

The pneumatic path of the RPT device <NUM> may comprise one or more air path items, e.g., an inlet air filter <NUM>, an inlet muffler <NUM>, a pressure generator <NUM> capable of supplying air at positive pressure (e.g., a blower <NUM>), an outlet muffler <NUM> and one or more transducers <NUM>, such as pressure sensors <NUM> and flow rate sensors <NUM>.

One or more of the air path items may be located within a removable unitary structure which will be referred to as a pneumatic block <NUM>. The pneumatic block <NUM> may be located within the external housing <NUM>. In one form a pneumatic block <NUM> is supported by, or formed as part of the chassis <NUM>.

The RPT device <NUM> may have an electrical power supply <NUM>, one or more input devices <NUM>, a central controller <NUM>, a therapy device controller <NUM>, a pressure generator <NUM>, one or more protection circuits <NUM>, memory <NUM>, transducers <NUM>, data communication interface <NUM> and one or more output devices <NUM>. Electrical components <NUM> may be mounted on a single Printed Circuit Board Assembly (PCBA) <NUM>. In an alternative form, the RPT device <NUM> may include more than one PCBA <NUM>.

An RPT device may comprise one or more of the following components in an integral unit. In an alternative form, one or more of the following components may be located as respective separate units.

An RPT device in accordance with one form of the present technology may include an air filter <NUM>, or a plurality of air filters <NUM>.

In one form, an inlet air filter <NUM> is located at the beginning of the pneumatic path upstream of a pressure generator <NUM>.

In one form, an outlet air filter <NUM>, for example an antibacterial filter, is located between an outlet of the pneumatic block <NUM> and a patient interface <NUM>.

An RPT device in accordance with one form of the present technology may include a muffler <NUM>, or a plurality of mufflers <NUM>.

In one form of the present technology, an inlet muffler <NUM> is located in the pneumatic path upstream of a pressure generator <NUM>.

In one form of the present technology, an outlet muffler <NUM> is located in the pneumatic path between the pressure generator <NUM> and a patient interface <NUM>.

In one form of the present technology, a pressure generator <NUM> for producing a flow, or a supply, of air at positive pressure is a controllable blower <NUM>. For example the blower <NUM> may include a brushless DC motor <NUM> with one or more impellers housed in a blower housing, such as in a volute. The blower may be capable of delivering a supply of air, for example at a rate of up to about <NUM> litres/minute, at a positive pressure in a range from about <NUM> cmH<NUM>O to about <NUM> cmH<NUM>O, or in other forms up to about <NUM> cmH<NUM>O. The blower may be as described in any one of the following patents or patent applications: <CIT>; <CIT>; <CIT>; and <CIT>.

The pressure generator <NUM> is under the control of the therapy device controller <NUM>.

In other forms, a pressure generator <NUM> may be a piston-driven pump, a pressure regulator connected to a high pressure source (e.g. compressed air reservoir), or a bellows.

Transducers may be internal of the RPT device, or external of the RPT device. External transducers may be located for example on or form part of the air circuit, e.g., the patient interface. External transducers may be in the form of noncontact sensors such as a Doppler radar movement sensor that transmit or transfer data to the RPT device.

In one form of the present technology, one or more transducers <NUM> are located upstream and/or downstream of the pressure generator <NUM>. The one or more transducers <NUM> may be constructed and arranged to generate signals representing properties of the flow of air such as a flow rate, a pressure or a temperature at that point in the pneumatic path.

In one form of the present technology, one or more transducers <NUM> may be located proximate to the patient interface <NUM>.

In one form, a signal from a transducer <NUM> may be filtered, such as by low-pass, high-pass or band-pass filtering.

A flow rate sensor <NUM> in accordance with the present technology may be based on a differential pressure transducer, for example, an SDP600 Series differential pressure transducer from SENSIRION.

In one form, a signal representing a flow rate from the flow rate sensor <NUM> is received by the central controller <NUM>.

A pressure sensor <NUM> in accordance with the present technology is located in fluid communication with the pneumatic path. An example of a suitable pressure sensor is a transducer from the HONEYWELL ASDX series. An alternative suitable pressure sensor is a transducer from the NPA Series from GENERAL ELECTRIC.

In one form, a signal from the pressure sensor <NUM> is received by the central controller <NUM>.

In one form of the present technology a motor speed transducer <NUM> is used to determine a rotational velocity of the motor <NUM> and/or the blower <NUM>. A motor speed signal from the motor speed transducer <NUM> may be provided to the therapy device controller <NUM>. The motor speed transducer <NUM> may, for example, be a speed sensor, such as a Hall effect sensor.

In one form of the present technology, an anti-spill back valve <NUM> is located between the humidifier <NUM> and the pneumatic block <NUM>. The anti-spill back valve is constructed and arranged to reduce the risk that water will flow upstream from the humidifier <NUM>, for example to the motor <NUM>.

A power supply <NUM> may be located internal or external of the external housing <NUM> of the RPT device <NUM>.

In one form of the present technology, power supply <NUM> provides electrical power to the RPT device <NUM> only. In another form of the present technology, power supply <NUM> provides electrical power to both RPT device <NUM> and humidifier <NUM>.

In one form of the present technology, an RPT device <NUM> includes one or more input devices <NUM> in the form of buttons, switches or dials to allow a person to interact with the device. The buttons, switches or dials may be physical devices, or software devices accessible via a touch screen. The buttons, switches or dials may, in one form, be physically connected to the external housing <NUM>, or may, in another form, be in wireless communication with a receiver that is in electrical connection to the central controller <NUM>.

In one form, the input device <NUM> may be constructed and arranged to allow a person to select a value and/or a menu option.

In one form of the present technology, the central controller <NUM> is one or a plurality of processors suitable to control an RPT device <NUM>.

Suitable processors may include an x86 INTEL processor, a processor based on ARM® Cortex®-M processor from ARM Holdings such as an STM32 series microcontroller from ST MICROELECTRONIC. In certain alternative forms of the present technology, a <NUM>-bit RISC CPU, such as an STR9 series microcontroller from ST MICROELECTRONICS or a <NUM>-bit RISC CPU such as a processor from the MSP430 family of microcontrollers, manufactured by TEXAS INSTRUMENTS may also be suitable.

In one form of the present technology, the central controller <NUM> is a dedicated electronic circuit.

In one form, the central controller <NUM> is an application-specific integrated circuit. In another form, the central controller <NUM> comprises discrete electronic components.

The central controller <NUM> may be configured to receive input signal(s) from one or more transducers <NUM>, one or more input devices <NUM>, and the humidifier <NUM>.

The central controller <NUM> may be configured to provide output signal(s) to one or more of an output device <NUM>, a therapy device controller <NUM>, a data communication interface <NUM>, and the humidifier <NUM>.

In some forms of the present technology, the central controller <NUM> is configured to implement the one or more methodologies described herein, such as the one or more algorithms <NUM> expressed as computer programs stored in a non-transitory computer readable storage medium, such as memory <NUM>. In some forms of the present technology, the central controller <NUM> may be integrated with an RPT device <NUM>. However, in some forms of the present technology, some methodologies may be performed by a remotely located device. For example, the remotely located device may determine control settings for a ventilator or detect respiratory related events by analysis of stored data such as from any of the sensors described herein.

The RPT device <NUM> may include a clock <NUM> that is connected to the central controller <NUM>.

In one form of the present technology, therapy device controller <NUM> is a therapy control module <NUM> that forms part of the algorithms <NUM> executed by the central controller <NUM>.

In one form of the present technology, therapy device controller <NUM> is a dedicated motor control integrated circuit. For example, in one form a MC33035 brushless DC motor controller, manufactured by ONSEMI is used.

The one or more protection circuits <NUM> in accordance with the present technology may comprise an electrical protection circuit, a temperature and/or pressure safety circuit.

In accordance with one form of the present technology the RPT device <NUM> includes memory <NUM>, e.g., non-volatile memory. In some forms, memory <NUM> may include battery powered static RAM. In some forms, memory <NUM> may include volatile RAM.

Memory <NUM> may be located on the PCBA <NUM>. Memory <NUM> may be in the form of EEPROM, or NAND flash.

Additionally or alternatively, RPT device <NUM> includes a removable form of memory <NUM>, for example a memory card made in accordance with the Secure Digital (SD) standard.

In one form of the present technology, the memory <NUM> acts as a non-transitory computer readable storage medium on which is stored computer program instructions expressing the one or more methodologies described herein, such as the one or more algorithms <NUM>.

In one form of the present technology, a data communication interface <NUM> is provided, and is connected to the central controller <NUM>. Data communication interface <NUM> may be connectable to a remote external communication network <NUM> and/or a local external communication network <NUM>. The remote external communication network <NUM> may be connectable to a remote external device <NUM>. The local external communication network <NUM> may be connectable to a local external device <NUM>.

In one form, data communication interface <NUM> is part of the central controller <NUM>. In another form, data communication interface <NUM> is separate from the central controller <NUM>, and may comprise an integrated circuit or a processor.

In one form, remote external communication network <NUM> is the Internet. The data communication interface <NUM> may use wired communication (e.g. via Ethernet, or optical fibre) or a wireless protocol (e.g. CDMA, GSM, LTE) to connect to the Internet.

In one form, local external communication network <NUM> utilises one or more communication standards, such as Bluetooth, or a consumer infrared protocol.

In one form, remote external device <NUM> is one or more computers, for example a cluster of networked computers. In one form, remote external device <NUM> may be virtual computers, rather than physical computers. In either case, such a remote external device <NUM> may be accessible to an appropriately authorised person such as a clinician.

The local external device <NUM> may be a personal computer, mobile phone, tablet or remote control.

An output device <NUM> in accordance with the present technology may take the form of one or more of a visual, audio and haptic unit. A visual display may be a Liquid Crystal Display (LCD) or Light Emitting Diode (LED) display.

A display driver <NUM> receives as an input the characters, symbols, or images intended for display on the display <NUM>, and converts them to commands that cause the display <NUM> to display those characters, symbols, or images.

A display <NUM> is configured to visually display characters, symbols, or images in response to commands received from the display driver <NUM>. For example, the display <NUM> may be an eight-segment display, in which case the display driver <NUM> converts each character or symbol, such as the figure "<NUM>", to eight logical signals indicating whether the eight respective segments are to be activated to display a particular character or symbol.

As mentioned above, in some forms of the present technology, the central controller <NUM> may be configured to implement one or more algorithms <NUM> expressed as computer programs stored in a non-transitory computer readable storage medium, such as memory <NUM>. The algorithms <NUM> are generally grouped into groups referred to as modules.

A pre-processing module <NUM> in accordance with one form of the present technology receives as an input a signal from a transducer <NUM>, for example a flow rate sensor <NUM> or pressure sensor <NUM>, and performs one or more process steps to calculate one or more output values that will be used as an input to another module, for example a therapy engine module <NUM>, and may be depicted as shown for example in <FIG>.

In one form of the present technology, the output values include the interface or mask pressure Pm, the respiratory flow rate Qr, and the leak flow rate Ql.

In various forms of the present technology, the pre-processing module <NUM> comprises one or more of the following algorithms: pressure compensation <NUM>, vent flow rate estimation <NUM>, leak flow rate estimation <NUM>, and respiratory flow rate estimation <NUM>.

In one form of the present technology, a pressure compensation algorithm <NUM> receives as an input a signal indicative of the pressure in the pneumatic path proximal to an outlet of the pneumatic block. The pressure compensation algorithm <NUM> estimates the pressure drop through the air circuit <NUM> and provides as an output an estimated pressure, Pm, in the patient interface <NUM>.

In one form of the present technology, a vent flow rate estimation algorithm <NUM> receives as an input an estimated pressure, Pm, in the patient interface <NUM> and estimates a vent flow rate of air, Qv, from a vent <NUM> in a patient interface <NUM>.

In one form of the present technology, a leak flow rate estimation algorithm <NUM> receives as an input a total flow rate, Qt, and a vent flow rate Qv, and provides as an output an estimate of the leak flow rate Ql. In one form, the leak flow rate estimation algorithm estimates the leak flow rate Ql by calculating an average of the difference between total flow rate Qt and vent flow rate Qv over a period sufficiently long to include several breathing cycles, e.g. about <NUM> seconds.

In one form, the leak flow rate estimation algorithm <NUM> receives as an input a total flow rate Qt, a vent flow rate Qv, and an estimated pressure, Pm, in the patient interface <NUM>, and provides as an output a leak flow rate Ql, by calculating a leak conductance, and determining a leak flow rate Ql to be a function of leak conductance and pressure, Pm. Leak conductance is calculated as the quotient of low pass filtered non-vent flow rate equal to the difference between total flow rate Qt and vent flow rate Qv, and low pass filtered square root of pressure Pm, where the low pass filter time constant has a value sufficiently long to include several breathing cycles, e.g. about <NUM> seconds. The leak flow rate Ql may be estimated as the product of leak conductance and a function of pressure, Pm.

A sudden change in leak is a change on a time scale that is shorter than the leak flow rate estimation algorithm <NUM> can initially keep up with, i.e. of the order of a breathing cycle or less. In certain therapy modes such sudden changes in leak need special handling, as described below.

In one form of the present technology, a respiratory flow rate estimation algorithm <NUM> receives as an input a total flow rate, Qt, a vent flow rate, Qv, and a leak flow rate, Ql, and estimates a respiratory flow rate of air, Qr, to the patient, by subtracting the vent flow rate Qv and the leak flow rate Ql from the total flow rate Qt.

In one form of the present technology, a therapy engine module <NUM> receives as inputs one or more of a pressure, Pm, in a patient interface <NUM>, and a respiratory flow rate of air to a patient, Qr, and provides as an output one or more therapy parameters.

In one form of the present technology, a therapy parameter is a treatment pressure Pt.

In one form of the present technology, therapy parameters are one or more of an amplitude of a pressure variation, a base pressure, and a target tidal volume.

In various forms, the therapy engine module <NUM> comprises one or more of the following algorithms: phase determination <NUM>, waveform determination <NUM>, tidal volume estimation <NUM>, and therapy parameter determination <NUM>.

In one form of the present technology, the RPT device <NUM> may determine breathing phase.

In one form of the present technology, a phase determination algorithm <NUM> receives as an input a signal indicative of respiratory flow rate, Qr, and provides as an output a phase Φ of a current breathing cycle of a patient <NUM>.

In some forms, known as discrete phase determination, the phase output Φ is a discrete variable. One implementation of discrete phase determination provides a bi-valued phase output Φ with values of either inhalation or exhalation, for example represented as values of <NUM> and <NUM> revolutions respectively, upon detecting the start of spontaneous inhalation and exhalation respectively. RPT devices <NUM> that "trigger" and "cycle" effectively perform discrete phase determination, since the trigger and cycle points are the instants at which the phase changes from exhalation to inhalation and from inhalation to exhalation, respectively. In one implementation of bi-valued phase determination, the phase output Φ is determined to have a discrete value of <NUM> (thereby "triggering" the RPT device <NUM>) when the respiratory flow rate Qr has a value that exceeds a positive threshold, and a discrete value of <NUM> revolutions (thereby "cycling" the RPT device <NUM>) when a respiratory flow rate Qr has a value that is more negative than a negative threshold. The inhalation time Ti and the exhalation time Te may be estimated as typical values over many respiratory cycles of the time spent with phase Φ equal to <NUM> (indicating inspiration) and <NUM> (indicating expiration) respectively.

Another implementation of discrete phase determination provides a tri-valued phase output Φ with a value of one of inhalation, mid-inspiratory pause, and exhalation.

In other forms, known as continuous phase determination, the phase output Φ is a continuous variable, for example varying from <NUM> to <NUM> revolutions, or <NUM> to 2π radians. RPT devices <NUM> that perform continuous phase determination may trigger and cycle when the continuous phase reaches <NUM> and <NUM> revolutions, respectively. In one implementation of continuous phase determination, the phase Φ is first discretely estimated from the respiratory flow rate Qr as described above, as are the inhalation time Ti and the exhalation time Te. The continuous phase Φ at any given instant may be determined as the half the proportion of the inhalation time Ti that has elapsed since the previous trigger instant, or <NUM> revolutions plus half the proportion of the exhalation time Te that has elapsed since the previous cycle instant (whichever instant was more recent).

In one form of the present technology, the therapy parameter determination algorithm <NUM> provides an approximately constant treatment pressure throughout a respiratory cycle of a patient.

In other forms of the present technology, the therapy control module <NUM> controls the pressure generator <NUM> to provide a treatment pressure Pt that varies as a function of phase Φ of a respiratory cycle of a patient according to a waveform template Π(Φ).

In one form of the present technology, a waveform determination algorithm <NUM> provides a waveform template Π(Φ) with values in the range [<NUM>, <NUM>] on the domain of phase values Φ provided by the phase determination algorithm <NUM> to be used by the therapy parameter determination algorithm <NUM>.

In one form, suitable for either discrete or continuously-valued phase, the waveform template Π(Φ) is a square-wave template, having a value of <NUM> for values of phase up to and including <NUM> revolutions, and a value of <NUM> for values of phase above <NUM> revolutions. In one form, suitable for continuously-valued phase, the waveform template Π(Φ) comprises two smoothly curved portions, namely a smoothly curved (e.g. raised cosine) rise from <NUM> to <NUM> for values of phase up to <NUM> revolutions, and a smoothly curved (e.g. exponential) decay from <NUM> to <NUM> for values of phase above <NUM> revolutions. In one form, suitable for continuously-valued phase, the waveform template Π(Φ) is based on a square wave, but with a smooth rise from <NUM> to <NUM> for values of phase up to a "rise time" that is less than <NUM> revolutions, and a smooth fall from <NUM> to <NUM> for values of phase within a "fall time" after <NUM> revolutions, with a "fall time" that is less than <NUM> revolutions.

In some forms of the present technology, the waveform determination algorithm <NUM> selects a waveform template Π(Φ) from a library of waveform templates, dependent on a setting of the RPT device. Each waveform template Π(Φ) in the library may be provided as a lookup table of values Π against phase values Φ. In other forms, the waveform determination algorithm <NUM> computes a waveform template Π(Φ) "on the fly" using a predetermined functional form, possibly parametrised by one or more parameters (e.g. time constant of an exponentially curved portion). The parameters of the functional form may be predetermined or dependent on a current state of the patient <NUM>.

In some forms of the present technology, suitable for discrete bi-valued phase of either inhalation (Φ = <NUM> revolutions) or exhalation (Φ = <NUM> revolutions), the waveform determination algorithm <NUM> computes a waveform template Π "on the fly" as a function of both discrete phase Φ and time t measured since the most recent trigger instant. In one such form, the waveform determination algorithm <NUM> computes the waveform template Π(Φ, t) in two portions (inspiratory and expiratory) as follows: <MAT>
where Πi(t) and Πe(t) are inspiratory and expiratory portions of the waveform template Π(Φ, t). In one such form, the inspiratory portion Πi(t) of the waveform template is a smooth rise from <NUM> to <NUM> parametrised by a rise time, and the expiratory portion Πe(t) of the waveform template is a smooth fall from <NUM> to <NUM> parametrised by a fall time.

In some forms of the present technology, the central controller <NUM> executes one or more tidal volume estimation algorithms <NUM> for the estimation of tidal volume using the values returned by one or more of the other algorithms in the therapy engine module <NUM>.

In one form of the present technology, the tidal volume estimation algorithm <NUM> receives as an input a signal indicative of respiratory flow rate Qr and the phase Φ determined by the phase determination algorithm <NUM>, and returns an estimate of the tidal volume VT of the most recent breath. The tidal volume VT may be estimated as the inspiratory (tidal) volume Vi for the breath, the expiratory (tidal) volume Ve for the breath, or some combination of the two, e.g. the mean or average. The inspiratory volume Vi may be estimated as the integral of the respiratory flow rate Qr over the inspiratory portion of the breath (indicated by phase Φ being less than <NUM>). The expiratory volume Ve may be estimated as the integral of the respiratory flow rate Qr over the expiratory portion of the breath (indicated by phase Φ being greater than or equal to <NUM>).

In some forms of the present technology, the central controller <NUM> executes one or more therapy parameter determination algorithms <NUM> for the determination of one or more therapy parameters using the values returned by one or more of the other algorithms in the therapy engine module <NUM>.

In one form of the present technology, the therapy parameter is an instantaneous treatment pressure Pt. In one implementation of this form, the therapy parameter determination algorithm <NUM> determines the treatment pressure Pt using the equation <MAT>
where:.

If the waveform determination algorithm <NUM> provides the waveform template Π(Φ, t) as a lookup table of values Π indexed by phase Φ, the therapy parameter determination algorithm <NUM> applies equation (<NUM>) by locating the nearest lookup table entry to the current value Φ of phase returned by the phase determination algorithm <NUM>, or by interpolation between the two entries straddling the current value Φ of phase.

The values of the amplitude A and the base pressure P<NUM> may be set by the therapy parameter determination algorithm <NUM> depending on the chosen respiratory pressure therapy mode in the manner described below.

The therapy control module <NUM> in accordance with one aspect of the present technology receives as inputs the therapy parameters from the therapy parameter determination algorithm <NUM> of the therapy engine module <NUM>, and controls the pressure generator <NUM> to deliver a flow of air in accordance with the therapy parameters.

In one form of the present technology, the therapy parameter is a treatment pressure Pt, and the therapy control module <NUM> controls the pressure generator <NUM> to deliver a flow of air whose mask pressure Pm at the patient interface <NUM> is equal to the treatment pressure Pt.

In one form of the present technology, the central controller <NUM> executes one or more methods <NUM> for the detection of fault conditions. The fault conditions detected by the one or more methods <NUM> may include at least one of the following:.

Upon detection of the fault condition, the corresponding algorithm <NUM> signals the presence of the fault by one or more of the following:.

An air circuit <NUM> in accordance with an aspect of the present technology is a conduit or a tube constructed and arranged to allow, in use, a flow of air to travel between two components such as the RPT device <NUM> and the patient interface <NUM>.

In particular, the air circuit <NUM> may be in fluid connection with the outlet of the pneumatic block <NUM> and the patient interface. The air circuit may be referred to as an air delivery tube. In some cases, there may be separate limbs of the circuit for inhalation and exhalation. In other cases, a single limb air circuit is used.

In one form of the present technology there is provided a humidifier <NUM> (e.g. as shown in <FIG>) to change the absolute humidity of air or gas for delivery to a patient relative to ambient air. Typically, the humidifier <NUM> is used to increase the absolute humidity and increase the temperature of the flow of air (relative to ambient air) before delivery to the patient's airways.

The humidifier <NUM> may comprise a humidifier reservoir <NUM>, a humidifier inlet <NUM> to receive a flow of air, and a humidifier outlet <NUM> to deliver a humidified flow of air. In some forms, as shown in <FIG>, an inlet and an outlet of the humidifier reservoir <NUM> may be the humidifier inlet <NUM> and the humidifier outlet <NUM> respectively. The humidifier <NUM> may further comprise a humidifier base <NUM>, which may be adapted to receive the humidifier reservoir <NUM> and comprise a heating element <NUM>.

<FIG> shows a model typical breath waveform of a person while sleeping. The horizontal axis is time, and the vertical axis is respiratory flow rate. While the parameter values may vary, a typical breath may have the following approximate values: tidal volume VT <NUM>, inhalation time Ti <NUM>, peak inspiratory flow rate Qpeak <NUM>/s, exhalation time Te <NUM>, peak expiratory flow rate Qpeak -<NUM>/s. The total duration of the breath Ttot is about <NUM>. The person typically breathes at a rate of about <NUM> breaths per minute (BPM), with Ventilation Vent about <NUM>/min. A typical duty cycle, the ratio of Ti to Ttot, is about <NUM>%.

Various respiratory pressure therapy modes may be implemented by the RPT device <NUM> depending on the values of the parameters A and P<NUM> in the treatment pressure equation (<NUM>) used by the therapy parameter determination algorithm <NUM> in one form of the present technology.

In some implementations of this form of the present technology, the amplitude A in the treatment pressure equation (<NUM>) is identically zero, so the treatment pressure Pt is identically equal to the base pressure P<NUM> throughout the respiratory cycle. Such implementations are generally grouped under the heading of CPAP therapy. In other implementations of this form of the present technology, the value of amplitude A in equation (<NUM>) is positive. Such implementations are known as bi-level therapy, because in determining the treatment pressure Pt using equation (<NUM>) with positive amplitude A, the therapy parameter determination algorithm <NUM> oscillates the treatment pressure Pt between two values or levels in synchrony with the spontaneous respiratory effort of the patient <NUM>. That is, based on the typical waveform templates Π(Φ, t) described above, the therapy parameter determination algorithm <NUM> increases the treatment pressure Pt to P<NUM> + A (known as the IPAP) at the start of, or during, or inspiration and decreases the treatment pressure Pt to the base pressure P<NUM> (known as the EPAP) at the start of, or during, expiration.

In some forms of bi-level therapy, the amplitude A is large enough that the RPT device <NUM> does some or all of the work of breathing of the patient <NUM>. Such forms may be referred to as providing ventilatory support to the patient <NUM>. In such forms, known as pressure support or pressure controlled ventilation therapy, the amplitude A is referred to as the pressure support, or swing. In pressure support ventilation therapy, the IPAP is the base pressure P<NUM> plus the pressure support A, and the EPAP is the base pressure P<NUM>.

In some forms of pressure support ventilation therapy, known as fixed pressure support ventilation therapy, the pressure support A is fixed at a predetermined value, e.g. <NUM> cmH<NUM>O. The predetermined pressure support value is a setting of the RPT device <NUM>, and may be set for example by hard-coding during configuration of the RPT device <NUM> or by manual entry through the input device <NUM>.

In other forms of pressure support ventilation therapy, broadly known as servo-ventilation, the therapy parameter determination algorithm <NUM> takes as input some currently measured or estimated parameter of the respiratory cycle and a target value of that respiratory parameter, and continuously adjusts the parameters of equation (<NUM>) to adjust the current measure of the respiratory parameter towards the target value. One example of servo-ventilation in which the respiratory parameter is tidal volume VT is sometimes referred to as safety volume mode.

In some forms of servo-ventilation, the therapy parameter determination algorithm <NUM> applies a servo-control methodology to repeatedly compute the pressure support A so as to adjust the current measure of the respiratory parameter towards the target value. One such servo-control methodology is Proportional-Integral (PI) control. In one implementation of PI control for safety volume mode, an adjustment ΔA to the current pressure support A is computed as: <MAT>
where G is the servo-control gain, Cnom is a nominal compliance constant (which is typically set to <NUM> / cmH<NUM>O for adults and to <NUM> / cmH<NUM>O for pediatrics, but may be varied for different patient sub-types) and VT(target) is the target tidal volume (in millilitres). The gain G is typically a constant value of one.

Other servo-control methodologies that may be applied by the therapy parameter determination algorithm <NUM> include proportional (P), proportional-differential (PD), and proportional-integral-differential (PID).

The value of the pressure support A computed via equation (<NUM>) may be clipped to a range defined as [Amin, Amax]. In this implementation, the pressure support A sits by default at the minimum pressure support Amin until the measure of tidal volume VT falls below the target tidal volume VT(target), at which point A starts increasing, only falling back to Amin when VT exceeds VT(target) once again.

The pressure support limits Amin and Amax are settings of the RPT device <NUM>, set for example by hard-coding during configuration of the RPT device <NUM> or by manual entry through the input device <NUM>.

Sudden change in leak (either the sudden appearance of a leak or its sudden resolution) may cause the estimate of leak flow rate Ql, and hence the respiratory flow rate estimate Qr, to be temporarily inaccurate while the leak flow rate estimation algorithm <NUM> "catches up" with the sudden change. When the leak appears, the respiratory flow rate Qr is overestimated for a period lasting perhaps a few breaths. Then, when the leak is resolved, the respiratory flow rate Qr is underestimated for a period. In addition, the phase determination algorithm <NUM> may be caused to overestimate or underestimate the inspiratory portions of the breaths respectively. The result is that when the leak appears, the inspiratory volume Vi tends to be temporarily overestimated and the expiratory volume Ve tends to be temporarily underestimated. When the leak is resolved, the expiratory volume Ve tends to be temporarily overestimated and the inspiratory volume Vi tends to be temporarily underestimated. In either case, the estimate of tidal volume VT by the tidal volume estimation algorithm <NUM> tends to be temporarily higher than the actual tidal volume. The result in safety volume mode is that pressure support A is either inappropriately reduced, or increased more slowly than it should be. <FIG> contains a graph <NUM> illustrating an example of such behaviour. The traces <NUM> to <NUM> in the graph <NUM> represent direct measurements of various breathing parameters, rather than those parameters as estimated by the RPT device <NUM> using the algorithms <NUM>. The top trace <NUM> represents the treatment pressure Pt, oscillating with amplitude equal to the pressure support A. The middle trace <NUM> represents the respiratory flow rate Qr, oscillating between positive (inspiration) and negative (expiration) portions. The lower trace <NUM> represents the integral of respiratory flow rate Qr, i.e. the instantaneous volume. The peak value of the peaks in the trace <NUM> therefore represents the tidal volume VT of each successive breath.

A leak suddenly appears at <NUM>. The pressure support falls significantly soon afterwards as the tidal volume is overestimated, before recovering to its previous value after a dozen or so breaths. The result is a temporary fall in the delivered tidal volume VT. The leak is resolved at <NUM>, and once again the pressure support falls significantly as the tidal volume is once again overestimated, taking many breaths to recover its previous value, while the delivered tidal volume VT also falls significantly.

In one form of the present technology, the servo-control gain G in equation (<NUM>) may be adjusted dynamically so that this effect of a sudden change in leak is reduced. As mentioned above, one effect of sudden leak appearance or resolution is to cause the estimates of inspiratory volume Vi and expiratory volume Ve to diverge temporarily. In one implementation, the servo-control gain G is therefore adjusted based on a difference between the estimates of inspiratory volume Vi and expiratory volume Ve, so as to generally decrease as the difference increases. In one such implementation, the servo-control gain G is adjusted linearly between its default value and a lower value Gmin as a relative differential tidal volume dv varies between a low value dvmin and a default value, e.g. <NUM>. <FIG> illustrates one example of such an adjustment of the servo-control gain G, where the default value is one, the low value Gmin is <NUM>, and the low value dvmin is also <NUM>. The relative differential tidal volume dv may be computed from the most recent breath as <MAT>
with adjustments to ensure the denominator is never zero.

By this implementation, the rate of adjustment of pressure support A is reduced as a sudden leak appearance or resolution causes the estimates of inspiratory volume Vi and expiratory volume Ve to diverge temporarily. Once these estimates converge as the leak flow rate estimation algorithm <NUM> catches up with the sudden leak change, the servo-control gain G returns to its normal value of one. The effects of the sudden leak change on the servo-control of pressure support are thus smoothed out, giving a more stable therapy in the face of sudden changes in leak.

<FIG> contains a graph <NUM> illustrating of the behaviour of the therapy parameter determination algorithm <NUM> in one such implementation of the present technology. As in <FIG>, the traces <NUM> to <NUM> in the graph <NUM> represent direct measurements of various breathing parameters, rather than those parameters as estimated by the RPT device <NUM> using the algorithms <NUM>. The top trace <NUM> represents the treatment pressure Pt, the middle trace <NUM> represents the respiratory flow rate Qr, and the lower trace <NUM> represents the integral of respiratory flow rate Qr, i.e. the instantaneous volume.

A leak suddenly appears at <NUM>, but the pressure support A falls far less than in the trace <NUM> at the same stage. As a result, the delivered tidal volume also falls by less than in the trace <NUM> at the same stage. The leak is resolved at <NUM>, and once again the pressure support A falls far less than in the trace <NUM>, resulting in a smaller fall in the delivered tidal volume than in the trace <NUM> at the same stage. The delivered tidal volume VT therefore varies significantly less in the face of the sudden leak changes.

<FIG> shows a high level flow chart of a method <NUM> of dynamically adjusting the servo-control gain G in the form of an algorithm that may be implemented in, or as a separate module of, a therapy engine module <NUM> in a respiratory therapy apparatus such as RPT <NUM>. At block <NUM>, the algorithm is invoked upon detection of a sudden change in leak. As shown in <FIG>, sudden leak detection may be made dependent on a change in pressure support or tidal volume. A sudden leak may be determined based on a rise in the relative differential tidal volume dv (see equation (<NUM>)) between the estimates of inspiratory volume Vi and expiratory volume Ve above some threshold dvmin over some predetermined time period (e.g., a single or multiple breaths). Upon detection of the sudden leak, the servo-control gain G of the apparatus is adjusted at block <NUM> based on a difference between estimated volume values Vi and Ve. As shown in <FIG> and as defined in equation (<NUM>), the adjustment may vary linearly between a default or normal upper value and a lower minimum value, Gmin based on a relative differential tidal volume dv. The gain G is thus adjusted dynamically in response to sudden leak which improves the performance of apparatus incorporating the technology by servo-controlling the degree of support in response to the sudden leak. Thus, the effect of the leak is reduced and therefore the impact of the leak on the operation in safety volume mode is also reduced and may be reflected in the change of ventilatory support provided.

At decision diamond <NUM>, the difference between Vi and Ve is examined to determine whether there has been convergence, e.g., the difference between Vi and Ve has converged within some predetermined limit such as relative difference of <NUM>% or less. If there is convergence, the gain G is then returned to its normal or default value (e.g. <NUM>) at block <NUM>. If there has been no convergence, then the gain G may be further adjusted at block <NUM> depending on the relative difference between the estimated inspiratory and expiratory volumes Vi, Ve. This allows for an additional level of dynamic adjustment. For example, until the convergence criterion is met, the gain G may be adjusted linearly based on the computed relative differential tidal volume dv as illustrated in <FIG>.

In an alternative implementation, blocks <NUM>, <NUM>, and <NUM> are not used, and block <NUM> is repeatedly invoked to adjust the servo-control gain G of the apparatus based on a difference between estimated volume values Vi and Ve.

As an example, a respiratory therapy apparatus that includes a pressure generator, transducer and controller may be configured to operate in accordance with an aspect of the present technology. In this example, the pressure generator would generate a flow of air or gas useful in providing ventilatory support to a patient. The transducer may they then generate a signal that represents one or more properties of the flow of air. A controller would then process or analyse the signal to estimate values for inspiratory and expiratory volumes of one or more patient breaths. The controller would also be configured to servo-control the ventilatory support to adjust an estimated tidal volume toward a target volume using a gain that dynamically adjusts based on a difference between the estimated values for inspiratory and expiratory volumes. This results in improvement relating to the adjustment of the estimated tidal volume in the presence of sudden leaks.

Ambient: In certain forms of the present technology, the term ambient will be taken to mean (i) external of the treatment system or patient, and (ii) immediately surrounding the treatment system or patient.

For example, ambient humidity with respect to a humidifier may be the humidity of air immediately surrounding the humidifier, e.g. the humidity in the room where a patient is sleeping. Such ambient humidity may be different to the humidity outside the room where a patient is sleeping.

In another example, ambient pressure may be the pressure immediately surrounding or external to the body.

In certain forms, ambient (e.g., acoustic) noise may be considered to be the background noise level in the room where a patient is located, other than for example, noise generated by an RPT device or emanating from a mask or patient interface. Ambient noise may be generated by sources outside the room.

Automatic Positive Airway Pressure (APAP) therapy: CPAP therapy in which the treatment pressure is automatically adjustable, e.g. from breath to breath, between minimum and maximum limits, depending on the presence or absence of indications of SDB events.

Continuous Positive Airway Pressure (CPAP) therapy: Respiratory pressure therapy in which the treatment pressure is approximately constant through a respiratory cycle of a patient. In some forms, the pressure at the entrance to the airways will be slightly higher during exhalation, and slightly lower during inhalation. In some forms, the pressure will vary between different respiratory cycles of the patient, for example, being increased in response to detection of indications of partial upper airway obstruction, and decreased in the absence of indications of partial upper airway obstruction.

Flow rate: The volume (or mass) of air delivered per unit time. Flow rate may refer to an instantaneous quantity. In some cases, a reference to flow rate will be a reference to a scalar quantity, namely a quantity having magnitude only. In other cases, a reference to flow rate will be a reference to a vector quantity, namely a quantity having both magnitude and direction. Flow rate may be given the symbol Q. 'Flow rate' is sometimes shortened to simply 'flow' or 'airflow'.

In the example of patient respiration, a flow rate may be nominally positive for the inspiratory portion of a breathing cycle of a patient, and hence negative for the expiratory portion of the breathing cycle of a patient. Total flow rate, Qt, is the flow rate of air leaving the RPT device. Vent flow rate, Qv, is the flow rate of air leaving a vent to allow washout of exhaled gases. Leak flow rate, Ql, is the flow rate of leak from a patient interface system or elsewhere. Respiratory flow rate, Qr, is the flow rate of air that is received into the patient's respiratory system.

Humidifier: The word humidifier will be taken to mean a humidifying apparatus constructed and arranged, or configured with a physical structure to be capable of providing a therapeutically beneficial amount of water (H<NUM>O) vapour to a flow of air to ameliorate a medical respiratory condition of a patient.

Leak: The word leak will be taken to be a flow of air to or from ambient other than through the elements of the air circuit. In one example, leak may occur as the result of an incomplete seal between a mask and a patient's face. In another example leak may occur in a swivel elbow to the ambient. Leak may also encompass the air exhaled to ambient around a tracheostomy tube in invasive ventilation.

Noise, conducted (acoustic): Conducted noise in the present document refers to noise which is carried to the patient by the pneumatic path, such as the air circuit and the patient interface as well as the air therein. In one form, conducted noise may be quantified by measuring sound pressure levels at the end of an air circuit.

Noise, radiated (acoustic): Radiated noise in the present document refers to noise which is carried to the patient by the ambient air. In one form, radiated noise may be quantified by measuring sound power/pressure levels of the object in question according to ISO <NUM>.

Noise, vent (acoustic): Vent noise in the present document refers to noise which is generated by the flow of air through any vents such as vent holes of the patient interface.

Patient: A person, whether or not they are suffering from a respiratory condition.

Pressure: Force per unit area. Pressure may be expressed in a range of units, including cmH<NUM>O, g-f/cm<NUM> and hectopascal. <NUM> cmH<NUM>O is equal to <NUM>-f/cm<NUM> and is approximately <NUM> hectopascal. In this specification, unless otherwise stated, pressure is given in units of cmH<NUM>O.

The pressure in the patient interface is given the symbol Pm, while the treatment pressure, which represents a target value to be achieved by the mask pressure Pm at the current instant of time, is given the symbol Pt.

Respiratory Pressure Therapy (RPT): The application of a supply of air to an entrance to the airways at a treatment pressure that is typically positive with respect to atmosphere.

Ventilator: A mechanical device that provides pressure support to a patient to perform some or all of the work of breathing.

Apnea: According to some definitions, an apnea is said to have occurred when flow falls below a predetermined threshold for a duration, e.g. <NUM> seconds. An obstructive apnea will be said to have occurred when, despite patient effort, some obstruction of the airway does not allow air to flow. A central apnea will be said to have occurred when an apnea is detected that is due to a reduction in breathing effort, or the absence of breathing effort, despite the airway being patent. A mixed apnea occurs when a reduction or absence of breathing effort coincides with an obstructed airway.

Breathing rate: The rate of spontaneous respiration of a patient, usually measured in breaths per minute.

Duty cycle: The ratio of inhalation time, Ti to total breath time, Ttot.

Effort (breathing): The work done by a spontaneously breathing person attempting to breathe.

Expiratory portion of a breathing cycle: The period from the start of expiratory flow to the start of inspiratory flow.

Flow limitation: Flow limitation will be taken to be the state of affairs in a patient's respiration where an increase in effort by the patient does not give rise to a corresponding increase in flow. Where flow limitation occurs during an inspiratory portion of the breathing cycle it may be described as inspiratory flow limitation. Where flow limitation occurs during an expiratory portion of the breathing cycle it may be described as expiratory flow limitation.

Hypopnea: According to some definitions, a hypopnea is taken to be a reduction in flow, but not a cessation of flow. In one form, a hypopnea may be said to have occurred when there is a reduction in flow below a threshold rate for a duration. A central hypopnea will be said to have occurred when a hypopnea is detected that is due to a reduction in breathing effort. In one form in adults, either of the following may be regarded as being hypopneas:.

Hyperpnea: An increase in flow to a level higher than normal.

Inspiratory portion of a breathing cycle: The period from the start of inspiratory flow to the start of expiratory flow will be taken to be the inspiratory portion of a breathing cycle.

Patency (airway): The degree of the airway being open, or the extent to which the airway is open. A patent airway is open. Airway patency may be quantified, for example with a value of one (<NUM>) being patent, and a value of zero (<NUM>), being closed (obstructed).

Positive End-Expiratory Pressure (PEEP): The pressure above atmosphere in the lungs that exists at the end of expiration.

Peak flow rate (Qpeak): The maximum value of flow rate during the inspiratory portion of the respiratory flow waveform.

Respiratory flow rate, patient airflow rate, respiratory airflow rate (Qr): These terms may be understood to refer to the RPT device's estimate of respiratory flow rate, as opposed to "true respiratory flow rate" or "true respiratory flow rate", which is the actual respiratory flow rate experienced by the patient, usually expressed in litres per minute.

Tidal volume (VT): The volume of air inhaled or exhaled during normal breathing, when extra effort is not applied. In principle the inspiratory volume Vi (the volume of air inhaled) is equal to the expiratory volume Ve (the volume of air exhaled), and therefore a single tidal volume VT may be defined as equal to either quantity. In practice the tidal volume VT is estimated as some combination, e.g. the mean, of these two quantities.

(inhalation) Time (Ti): The duration of the inspiratory portion of the respiratory flow rate waveform.

(exhalation) Time (Te): The duration of the expiratory portion of the respiratory flow rate waveform.

(total) Time (Ttot): The total duration between the start of one inspiratory portion of a respiratory flow rate waveform and the start of the following inspiratory portion of the respiratory flow rate waveform.

Typical recent ventilation: The value of ventilation around which recent values of ventilation Vent over some predetermined timescale tend to cluster, that is, a measure of the central tendency of the recent values of ventilation.

Upper airway obstruction (UAO): includes both partial and total upper airway obstruction. This may be associated with a state of flow limitation, in which the flow rate increases only slightly or may even decrease as the pressure difference across the upper airway increases (Starling resistor behaviour).

Ventilation (Vent): A measure of a rate of gas being exchanged by the patient's respiratory system. Measures of ventilation may include one or both of inspiratory and expiratory flow, per unit time. When expressed as a volume per minute, this quantity is often referred to as "minute ventilation". Minute ventilation is sometimes given simply as a volume, understood to be the volume per minute.

Adaptive Servo-Ventilator (ASV): A servo-ventilator that has a changeable, rather than fixed target property. The changeable target property may be learned from some characteristic of the patient, for example, a respiratory characteristic of the patient.

Backup rate: A parameter of a ventilator that establishes the minimum breathing rate (typically in number of breaths per minute) that the ventilator will deliver to the patient, if not triggered by spontaneous respiratory effort.

Cycled: The termination of a ventilator's inspiratory phase. When a ventilator delivers a breath to a spontaneously breathing patient, at the end of the inspiratory portion of the breathing cycle, the ventilator is said to be cycled to stop delivering the breath.

Expiratory positive airway pressure (EPAP): a base pressure, to which a pressure varying within the breath is added to produce the desired mask pressure which the ventilator will attempt to achieve at a given time.

End expiratory pressure (EEP): Desired mask pressure which the ventilator will attempt to achieve at the end of the expiratory portion of the breath. If the pressure waveform template Π(Φ) is zero-valued at the end of expiration, i.e. Π(Φ) = <NUM> when Φ = <NUM>, the EEP is equal to the EPAP.

Inspiratory positive airway pressure (IPAP): Maximum desired mask pressure which the ventilator will attempt to achieve during the inspiratory portion of the breath.

Pressure support: A number that is indicative of the increase in pressure during ventilator inspiration over that during ventilator expiration, and generally means the difference in pressure between the maximum value during inspiration and the base pressure (e.g., PS = IPAP - EPAP). In some contexts pressure support means the difference which the ventilator aims to achieve, rather than what it actually achieves.

Servo-ventilator: A ventilator that measures or estimates some parameter of the patient's respiratory cycle and adjusts the level of pressure support to adjust the measured parameter towards a target value of the parameter.

Spontaneous/Timed (S/T): A mode of a ventilator or other device that attempts to detect the initiation of a breath of a spontaneously breathing patient. If however, the device is unable to detect a breath within a predetermined period of time, the device will automatically initiate delivery of the breath.

Swing: Equivalent term to pressure support.

Triggered: When a ventilator delivers a breath of air to a spontaneously breathing patient, it is said to be triggered to do so at the initiation of the respiratory portion of the breathing cycle by the patient's efforts.

All publications mentioned herein describe the methods and/or materials which are the subject of those publications. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present technology is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed.

The terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced.

Although the technology herein has been described with reference to particular examples, it is to be understood that these examples are merely illustrative of the principles and applications of the technology. In some instances, the terminology and symbols may imply specific details that are not required to practice the technology. For example, although the terms "first" and "second" may be used, unless otherwise specified, they are not intended to indicate any order but may be utilised to distinguish between distinct elements. Furthermore, although process steps in the methodologies may be described or illustrated in an order, such an ordering is not required. Those skilled in the art will recognize that such ordering may be modified and/or aspects thereof may be conducted concurrently or even synchronously.

It is therefore to be understood that numerous modifications may be made to the illustrative examples and that other arrangements may be devised without departing from the scope of the technology.

Claim 1:
A non-transitory computer readable storage medium (<NUM>) with program instructions that, when executed by a controller (<NUM>), cause the controller (<NUM>) to perform a method of operating a respiratory treatment apparatus (<NUM>), the method comprising:
controlling generation, by a pressure generator (<NUM>) of the respiratory treatment apparatus (<NUM>), of a flow of air so as to provide ventilatory support to a patient; and
adjusting a servo-control gain for the ventilatory support based on a difference between an estimated inspiratory volume and an estimated expiratory volume of a breath of the patient, upon detection of a sudden leak in the respiratory treatment apparatus (<NUM>).