Patent Application
20170304570
In respiratory medicine, ventilation devices are typically used to deliver respiratory gases for therapeutic effect. Ventilators have been used with invasive patient interface, such as endotracheal tubes. Bi-level, Bi-PAP, and CPAP devices have been used with non-invasive patient interfaces, such as respiratory masks. When an option, non-invasive respiratory systems are preferred for increased patient comfort and reduced risks. Non-invasive ventilation (NIV) systems such as Bi-Level PAP (positive airway pressure) require the use of a sealed patient interface, such as a full face mask. Systems with patient interface that seal on the patient (i.e. closed systems) can generate higher pressures with low flows or non-continuous flows. Sealed patient interfaces are not as comfortable or easy to apply as non-sealed patient interface, such as nasal cannulas. However, non-sealing nasal cannulas do not work properly with NIV systems. Nasal cannulas are typically used with basic oxygen delivery systems that have flow limitations for various reasons.
There is a need for a respiratory gas delivery system that works optimally with non-sealing patient interfaces to produce therapeutic effects to the patient similar to that of NIV systems. Because the system has a non-sealing patient interface and therefore some gas and pressure is lost to atmosphere, this respiratory gas delivery system must be able to deliver gas at high flows that are high enough to generate positive pressure in the patient's airway.
The present disclosure relates to a high flow therapy system for delivering heated and humidified respiratory gas to an airway of a patient, the system including a respiratory gas flow pathway for delivering the respiratory gas to the airway of the patient by way of a non-sealing respiratory interface; wherein flow rate of the pressurized respiratory gas is controlled by a microprocessor.
The present invention is a respiratory gas delivery system that delivers high flows (i.e. high flow therapy) through a non-sealing patient interface. This High Flow Therapy (HFT) system is comprised of a HFT device (i.e. the main device) and its accessories, which are described in further detail throughout. The HFT device can provide respiratory support for patients ranging from neonates to adults. The HFT device can lower respiratory rates, improve secretion clearance, and reduce the work of breathing. The HFT device can relieve respiratory disorders that respond to certain levels of positive airway pressures, such as asthma, bronchitis, sleep apnea, snoring, COPD, and other conditions of the respiratory tract. For example, the HFT system could deliver up to 35 cm H2O of airway pressure. The HFT device can treat hypothermia and aid in washout of anesthetics after surgery. It is envisioned that the HFT device may have applications similar to those prescribed hypobaric chambers, such as brain or head injury (e.g. concussions). The present disclosure relates to a high flow therapy system for delivering heated and humidified respiratory gas to an airway of a patient. The HFT device can generate flows that are continuous. The HFT system delivers the gases to the patient via a non-sealing patient interface (e.g. nasal cannula) utilizing an “open flow” method of delivery. “Open Flow” specifies that the cannula in the patient's nose does not create a seal or near seal.
The HFT device is an all-in-one device that allows for control of gas flow, gas oxygen concentration, gas temperature, and gas humidity in a single device or system. This includes delivering gases at flow rates up to 60 L/min, oxygen concentrations up to 100%, gases heated from 30 to 40 degrees Celsius, and humidified gases up to 100% relative humidity. The is vastly superior to basic oxygen delivery systems that are limited to gas flows of up to 8 L/min, have no gas temperature control, and have no gas humidity control. Because basic oxygen delivery systems have no gas temperature or gas humidity control, gas flows higher than 8 L/min are not well tolerated by the patient. In contrast, the HFT device can deliver higher flow rates that are easily tolerated in the nasal passages when the gas is warm and humid. The high flow also assures that the patient's inspired volume may be almost entirely derived from the gas delivered (i.e. minimized or no mixture of delivered gas with ambient air). The HFT system may generate a positive pressure in the airways during inhalation and/or exhalation, even though the system is an open system (i.e. does not use a sealing patient interface).
An all-in-one HFT device allows for more control and more accuracy of the gas conditions being delivered. It also provides the opportunity to provide feedback to the operator and to provide feedback loop control of the HFT device through for example gas sensing. Finally, an all-in-one HFT device allows for improved communications and alarms to the operator. For example, the HFT device may gather airway pressure information through its pressure sensing technology described throughout and use that information to adjust flow rates (either manually by the operator or automatically by the HFT device) in order to control airway pressures (e.g. prevent unintended high pressures).
The HFT system is a microprocessor-controlled respiratory gas delivery system that provides continuous flows of heated and/or humidified air and/or oxygen mixtures to patients. The HFT device can be controlled by a microprocessor on a main PCB (printed circuit board). The operator of the HFT device inputs settings, such as gas flow rate, gas temperature, gas oxygen concentration, gas humidity levels, etc. via the HFT device's user interface for the microprocessor to control. The user interface may be a graphical user interface (GUI). The user interface may contain information such as graphs (e.g. pressure waveform), numbers, alpha characters, help menus, etc. The user interface may be shown on a display. The display can have a touch screen that allows the operator make inputs to the HFT device. The display can be rotated, for example up to 360 degrees, to facilitate viewing or entry. The display can be pivoted or tilted, for example from 0 to 180 degrees, to facilitate viewing, entry, or shipping. The display can be removable to facilitate shipping, servicing, or to be used as a portable user interface. The HFT device can also include push buttons or knobs as part of the user interface system. In alternative embodiments, the information on the display may be projected by the HFT device (e.g. on a wall or on a table) or the information may be transmitted onto another device, such as a hand held device or computer. In another alternative embodiment a separate device, such as phone, tablet, or computer may couple with the HFT device in lieu of the display or may transmit information to the HFT device in order to serve as the user interface.
The HFT device may have a battery so that it may work, at least partially, as a portable device, without being plugged in, or without wall power (e.g. as a backup battery in a power outage). The HFT device may be mounted on a pole, on a cart, or may be configured to be placed on a table, desk, or nightstand.
Medical grade air and/or medical grade oxygen, for example from hospital gas supply systems or compressed gas tanks, may be used with the HFT system. Other gases, such as helium, may be substituted for the air or oxygen. An inlet filter (e.g. a water trap) can be connected between a gas source and the HFT device via a fitting (e.g. DISS fitting). The inlet filter could be internal or conversely external to the HFT device so it is visible and accessible for service. The pressurized gas (e.g. air or oxygen from the facility at 50 psi) then enters the HFT device and its flow system.
The HFT device can have an integrated flow adjustment system to deliver the set flow rate and/or oxygen concentrations to the patient. Flow control can be achieved automatically through the interaction between the system electronics (e.g. the microprocessor) and the flow system. The flow system can consist of valve systems. Valve systems can be used for air and/or oxygen gas flow regulating and metering. The valve systems can be partially or completely enclosed in the HFT device.
A valve system can be a manifold (e.g. a molded housing or machined block of plastic or aluminum). A manifold can have one manifold inlet, one manifold outlet, and one manifold flow path there between. In an alternate embodiment, a single manifold can have a first manifold inlet, a first manifold outlet, and a first manifold flow path there between, as well as a second manifold inlet, a second manifold outlet, and a second manifold flow path there between. In a preferred embodiment, there are two manifolds inside the unit—one for air and one for oxygen. A regulator can be mounted on the manifold. The regulator can reduce the gas pressure from its initial pressure (e.g. 50 psi) to a lower or constant pressure that is optimal for subsequent flow rate control inside the device. The pressurized gas flows from the manifold inlet to the regulator that is mounted on the manifold. After leaving the regulator, the gas flows through a proportional valve that can also be mounted on the manifold. The proportional valve can be a piezo-actuated proportional valve. The proportional valve can output a gas flow rate proportional to a signal voltage. The proportional valve is normally closed when no gas flow is required through the valve. In a preferred embodiment, each valve system can have two proportional valves, where a first proportional valve accommodates higher flow rates (e.g. 50 L/min) and a second proportional valve accommodates lower flow rates (e.g. 1 L/min). In this embodiment, the two proportional valves may work independently or may work in cooperation.
The valve system can have a mass flow sensor coupled with the manifold to measure the flow rate of the gas. The mass flow sensor is coupled to a manifold PCB, which can be mounted to the manifold. The manifold printed circuit board is electrically connected to the main PCB communicate input/output signals and power. This system can be referred to as a 2-position (i.e. on and off), 2-way (i.e. gas in and gas out) piezo-based valve system with integral mass flow metering system. This system can be described as a low-power, highly-sensitive piezo valve working in conjunction with a mass flow sensor and with control loop electronics to achieve accurate flow rates with little power consumption. The results are that the valve systems can be very quiet and cool, eliminating the needs for fans or secondary cooling devices (e.g. heat sinks) inside the HFT device. This integrated flow adjustment system described in the sections above forms a control loop by which the gas flow may be adjusted by the software of the HFT device.
Gas exists the manifold through the manifold outlet. In an embodiment with two manifolds (i.e. one for each gas), the gases exit their respective manifolds and stream together to mix. This mixing can occur in a tube, a mixing chamber, a blender, etc. In an embodiment with one manifold for two different gases, the gases may stream together within the manifold to mix prior to exiting the manifold (i.e. two manifold inlets and one manifold outlet).
In another embodiments, the HFT device can entrain air from ambient instead of receiving it from a compressed gas source. In yet another embodiment, the HFT device can have an integral blower for air to advance the gas. Both of these embodiments could replace the air valve system and integrate with the flow adjustment system. Gas from these embodiments could still mix with the oxygen downstream as previously described.
Mixed gases can then proceed towards and through an outlet adapter. Pressure inside the outlet adapter can be measured by a drive pressure sensor. The drive pressure sensor can be located on the main PCB and can be pneumatically connected to the bore of the outlet adapter by a length of flexible tubing. If the pressure inside the outlet adapter exceeds a certain pressure (e.g. 1 psi), the gas may be vented out of the outlet adapter through a relief valve.
The end of the outlet adapter may protrude outside the HFT device enclosure. The outlet adapter can feature an oxygen analyzer port into which an oxygen analyzer may be connected to for oxygen concentration (e.g. FiO2) verification purposes. The oxygen analyzer port may be closed by a valve, plug, or cap when an analyzer is not in use. Such a feature may be coupled or integral with the outlet adapter to close of the oxygen analyzer port. An analyzer adapter may be inserted into the oxygen analyzer port to allow the fit of different sizes of oxygen analyzers. This analyzer adapter may be integrated into the outlet adapter.
An outlet filter may be connected to the outlet adapter (e.g. via press fit). This outlet filter may have viral and/or anti-bacterial properties. The outlet filter serves to keep bacteria, viruses, volatile organic compounds, etc. from entering the water chamber and eventually reaching the patient. The outlet filter also serves to keep water, humidity, bacteria, viruses, etc. from entering the HFT device itself. This keeps undesirable matter from collecting inside the HFT device and potentially being transmitted to the next patient that uses the HFT device. The outlet filter therefore is a safety component to reduce risks to the HFT device and the patient from use of the HFT device. The outlet filter may have a filter gas sampling port. The outlet filter may have a straight, angled, or staggered filter body portion, filter inlet gas port, and/or filter outlet gas port. The end of the outlet adapter may be closed by a valve, plug, or cap when the outlet filter is not engaged, for example between use of the HFT device on different patients. Such a feature may be coupled or integral with the outlet adapter and would serve to protect the inside of the HFT device when an outlet adapter is not present.
The outlet filter and the other components downstream may be considered single use, single patient use, or disposable components. These components may include a water chamber, a delivery circuit, a patient interface (e.g. cannula; mask; or artificial airways such as endotracheal tubes, nasotracheal tubes, and tracheotomy tubes), a tee, and/or other fittings. It is preferred that the patient interface be a non-sealing interface (i.e. not intended to form a substantial seal with the patient), such as a non-sealing nasal cannula.
The water chamber slides into the HFT device and subsequently engages with outlet filter (via a friction fit). The HFT device has receiving flanges that couple with the water chamber. The receiving flanges can be spring loaded to facilitate securing the water chamber and/or to facilitate keeping contact between the contact plate and the base plate. The water chamber can maintain in the HFT device via an upward force and/or friction between the water chamber and the HFT device. The water chamber can be inserted or removed without having to manipulate (e.g. press down) another feature, such as latch or bar.
The water chamber has a water chamber gas inlet and an water chamber gas outlet. The water chamber gas inlet can have a water chamber gas inlet axis and the water chamber gas outlet can have a water chamber gas outlet axis. The water chamber gas inlet axis and the water chamber gas outlet axis may be parallel. Further, a plane drawn between the water chamber gas inlet axis and the water chamber gas outlet axis may be parallel to a typical table, nightstand, or desk located in the use environment, a platform on a cart or I.V. pole where the HFT device may be placed during use, or the bottom of the HFT device itself. The gas moves through the water chamber picking up heat and/or humidity and then into the delivery circuit. It is preferred that the humidified gas that exits either the water chamber not enter into or through a portion of the HFT device itself to avoid risk of contamination or the need to clean or disinfect that portion of the HFT device prior to use on another patient.
The water chamber can consist of a clear housing (e.g. made of a resin such as polystyrene) that allows the operator to see the water level inside. The water chamber can have a base plate (e.g. made of metal such as aluminum). The base plate may be bonded to the housing (e.g. UV cured adhesive). In an alternate embodiment, a gasket (e.g. an o-ring) may be used to couple and/or seal the base plate to the housing. The water chamber may have an inlet baffle on the water chamber gas inlet to prevent water from splashing towards the outlet filter. The water chamber may have an outlet baffle on the water chamber gas outlet to prevent water from splashing towards the delivery circuit, for example during movement or transportation of the HFT device.
The operator may fill the water chamber manually with water up to a maximum level, which may be indicated by markings on the water chamber. In a preferred embodiment, the water chamber may have an automatic filling system to replace the otherwise manual process of filling the water chamber with water from a sterile water bag that is suspended above the HFT system. In a manual arrangement, the operator must attend to the device periodically, as needed, in order to verify that the water chamber is being kept at a water level that is adequate for the device to function normally. If the water level is too low, water must be added to the water chamber. The manual filling process usually involves the operator physically releasing a pinch valve (or other valve mechanism) that normally impedes water flow from the sterile water bag's tubing and waiting a few moments for the water chamber to fill to the correct level before re-closing the valve. Maintaining a water level that is adequate for normal device function is necessary to prevent unwanted interruptions to therapy. If the water chamber is allowed to reach a very low level or empty water level, the device may signal an audible alert. If the low water condition is not addressed in time, the device may either continue to supply under-humidified respiratory gas or may automatically pause the gas delivery until the condition is resolved. The advantages of an automatic filling system is that it ensures an adequate water level (e.g. a continuous level, such as a predetermined minimum level) in the water chamber until the sterile bag is empty and that it eliminates the need for operator involvement in the interim. With the automatic filling system, when the water is released into the water chamber from the water bag, the water level inside the water chamber will rise until a plastic float component inside seals the fill port. As the water is consumed by the heated humidification process, the water level falls and the float lowers, allowing more water from the water bag to fill the water chamber again until the port is re-sealed. If left unattended, this process will continue until the water bag is completely empty.
The delivery circuit provides a conduit for the heated and/or humidified respiratory gas as the gas is transported from the water chamber to the patient interface. The delivery circuit may have a heating element inside, such as a heated wire. The heated wire may extend through some or all of the delivery circuit. The heated wire may be straight, coiled like a spring, or embedded in the delivery circuit. The delivery circuit actively maintains the desired humidity and temperature parameters of the gas and prevents and/or minimizes rainout or excessive moisture condensation inside the delivery circuit. Rainout is a concern for the safety of the patient.
The delivery circuit can have a first connector, a second connector, and a tube (e.g. a corrugated tube) there between. The first connector can connect the delivery circuit to the water chamber. The first connector may have a body that is rigid and provides structure, such as a plastic, and that houses electrical contacts. The electrical contacts may be integrally molded into the body. Alternatively, the body may be flexible, have a flexible portion (e.g. by overmolding), or have a flexible portion that is coupled with the rigid portion. The first connector (or its flexible portion) portion can facilitate sealing and/or coupling the first connector with the water chamber. The first connector (or its flexible portion) can facilitate coupling the delivery circuit to the enclosure of the HFT device. For example, the flexible portion conforms to a mating socket in the enclosure of the HFT device to provide a snug, secure mechanical engagement. The delivery circuit may couple with the HFT device or the water chamber via a friction fit. The first connector (through either the rigid portion or the flexible portion) can provide a hand-grip for the user to insert or remove the delivery circuit from the water chamber and/or the HFT device.
The delivery circuit can also have a long, flexible sensing conduit (and/or or a sampling conduit in other embodiments) that is internal to the delivery circuit (i.e. routed through the annular flow path through the tube). In an alternate embodiment, the sensing conduit may be external (but possibly coupled) to the delivery circuit. In another alternate embodiment, the tube could be a multiple lumen tube where a first lumen is the gas delivery path, a second lumen is the sensing conduit (or a sampling conduit), and possibly a third lumen is a sampling conduit. The sensing conduit can pneumatically connect the HFT device (via a sensor port on its enclosure) to the distal end of the patient interface. The use of a sensing conduit (or sampling conduit) can allow all electrical sensing components required for signal processing to remain inside the HFT device with the other electronics, rather than having electrical sensing components in one of the disposable components (e.g. on the distal end of the patient interface).
When the delivery circuit is coupled with the HFT device, a seal can be created between the sensor port on the HFT device and the sensing conduit in the delivery circuit. The delivery circuit or the HFT device may have a seal (e.g. o-ring) to facilitate this seal. When the delivery circuit is coupled with the enclosure of HFT device, the electrical contacts on the delivery circuit can engage with electrical contacts on the HFT device. This electrical engagement can enables the control of the thermal components in the delivery circuit by the software of the HFT device to maintain the desired temperature and humidity parameters of the gas. The delivery circuit may also have at least two temperature sensors (e.g. thermistors) internally. A first thermistor can be located near the first connector and a second thermistor can be located near the second connector. The thermistors can provide temperature feedback to the main PCB via the electrical contact engagement between the delivery circuit and the HFT device. The heated wire is powered by the HFT device via the electrical contact engagement between the delivery circuit and the HFT device.
The delivery circuit can have a holder internal and near the second connector. The holder can couple the second thermistor and/or the heating wire. The holder can provide a means for pulling the second thermistor and/or the heating wire through the delivery circuit towards the second connector. The holder can maintain a specific distance between the heated wire and the second thermistor to ensure that the gas temperature reading by the second thermistor is not influenced or made inaccurate by the temperature of the heated wire. The heated wire can bend or wrap around the holder to facilitate the return of the heated wire back to the first connector. The holder can couple to the tube, for example by having a protrusion (i.e. a ring or partial ring) that inserts into at least one of the corrugations on the tube or can couple with the second connector. The holder can provide a means for positioning the holder at a specific location within the tube or a certain distance from the second connector. The second connector can have a port to connect the sensing conduit.
The patient interface may have a nasal cannula portion that is intended to enter the nasal passages. The patient interface may have a first conduit for delivering the respiratory gas. The patient interface may have a second conduit for sensing or sampling (e.g. collecting pressure data in the nasal passages via the nasal cannula portion). The patient interface may mechanically and fluidically couple with the delivery circuit via a friction fit. The patient interface may have a patient fitting that may couple with the second connector. When the patient interface is coupled with the delivery circuit, a seal can be created between the sensing conduit in the delivery circuit and a fitting sensing conduit in the patient fitting. The fitting sensing conduit in the patient fitting pneumatically couples or communicates with second conduit. Therefore, the second conduit can be in communication with the sensing port on the HFT device. The patient interface can be described as a sensing-enabled nasal cannula patient interface. In one embodiment, the fitting sensing conduit in the patient fitting can split into two fitting sensing conduits, which can pneumatically couple with two sensing conduits. The nasal cannula and the patient fitting can be connected by one or more patient tubes. A patient tube may be single or double lumen. A double lumen patient tube may have a first lumen for gas delivery and a second lumen for sensing or sampling.
The main PCB of the HFT device may have a sensor for taking measurements at or proximal the outlet of the patient interface. In one embodiment, the sensor can be a pressure sensor for measuring the airway pressure of the user. In this embodiment, the delivery circuit and the patient interface can have a conduit system that communicates with the pressure sensor. This would allow the HFT system to monitor and/or control pressure. In an alternate embodiment, the sensor can be for sampling the gas at or proximal the outlet of the patient interface. For example, the gas exhaled by the user may be sampled for CO2 content. In a similar manner to the pressure sensor embodiment, the delivery circuit and the patient interface would have a conduit system that communicates with the sampling sensor.
Different versions of delivery circuit can couple with the HFT device. As mentioned throughout, a delivery circuit can have thermal, electrical, temperature sensing, pressure sensing, and/or gas sampling capabilities and/or conduits in addition to its gas delivery function. The HFT device can be configured to recognize what type of delivery circuit is being connected to the device. For example, when a delivery circuit with gas delivery, electrical, and pressure sensing capabilities is connected, the HFT device could recognize this type of delivery circuit and consequently activate the pressure sensing aspects of the HFT device, such as pressure sensing graphics, alarms, etc. Different delivery circuits with different capabilities then could serve to activate different and various functionality of the HFT device, which may exist in the HFT device but be dormant or inactive depending on the delivery circuit connected. The HFT device may have mechanical, electrical, or optical means for recognizing the delivery circuit type connected. In one embodiment, the delivery circuit may depress certain switch on the HFT device or may contact certain electrical contacts on the HFT device. In another embodiment, the HFT device may optically read a certain delivery circuit or may scan a feature (e.g. a barcode or serial number) on a certain delivery circuit. In one example, if an operator tried to connect a delivery circuit not authorized or compatible with the HFT device (e.g. a delivery circuit connected to a sealed patient interface), the HFT device may be programmed to have limited function or not function at all. In an alternate example, if an operator tried to connect a delivery circuit connected to a sealed patient interface, the HFT device may be programmed to switch to a bi-level or Bi-PAP mode (e.g. pressure based mode) instead of an HFT mode (e.g. flow based mode) and actually allow use with a sealed mask like a CPAP, Bi-PAP, or a ventilator.
The disposable components, such as the outlet filter, water chamber, delivery circuit, and patient interface, may be individually removed from the HFT device system after use. Alternatively, groups of these disposable devices may be removed at the same time. For example, the outlet filter may be decoupled from the HFT device in one motion to disengage the water chamber, delivery circuit, and patient interface at the same time. This is advantageous to simply the disassembly, as well as to minimize the amount of water or other contents in the disposable components that may be inadvertently leaked into the environment during disassembly.
The HFT device may further serve as a diagnostic device either during its typical HFT use or while it not being used for typical HFT treatment. The HFT device could utilize the previously mentioned sensing capabilities (e.g. pressure sensing, gas sampling, etc.) for diagnostic applications. For example, the HFT device may be used to diagnosis respiratory alignments such as sleep apnea. The HFT device could monitor, measure, record, and output the necessary information. The HFT device could incorporate functionality or accessories to include determination of stage of sleep, for example via electroencephalogram (EEG), electro-oculogram (EOG), submental electromyogram (EMG) and/or electrocardiogram/heart rate (ECG). The HFT device could incorporate functionality or accessories to include sleep parameters such as airflow, respiratory movement/effort, oxygen saturation (e.g. by oximetry), snoring, pulse rate, head movement, head position, limb movement, actigraphy, and/or peripheral arterial tone. Diagnostic accessories coupled with the HFT device could include a body sensors, pulse oximeter, a wearable wrist device, a chest or abdomen band or belt, headgear, thermistor, nasal cannula, and/or nasal/oral oral cannula, any of these which may have integrated sensors or sensing technology.
The HFT device may receive information (e.g. software upgrades) via a wired connection, USB, memory card, fiber optic, wireless connection, blue tooth, Wi-Fi, etc. The HFT device may send information (e.g. patient reports) via similar communication means. A wired connection such as USB or memory card, or a wireless connection such as blue tooth or Wi-Fi.
The bulk of the work of heating the respiratory gas can be done by the heater (e.g. PTC heater element) that is part of the HFT device. This heater can be concealed by a cover plate (e.g. stainless steel material) of the HFT device, which may be in direct contact with the base plate (e.g. aluminum material) of the water chamber during use. During the heating process, the duty cycle of the heater and/or the heated wire is precisely and continuously adjusted by the HFT device's embedded software in response to feedback supplied by a temperature sensor that is located near the heater (and in some embodiments may be in contact with the cover plate) and/or in response to the feedback supplied by the thermistors in the delivery circuit.
The HFT device may periodically decrease the gas flow rate from the set gas flow rate to allow the lungs to temporarily return to a more normal resting volume. The HFT device may automatically lower the gas flow by a certain percentage or by a certain value from the set gas flow value for a specific amount of time over a certain frequency or time period. For example, the HFT device may automatically lower the gas flow by a 20% or by 5 L/min for five seconds every ten minutes. Alternatively, the HFT device may automatically adjust the gas flow by a certain percentage, by a certain value, or a certain multiple of the expected patient tidal volume, for example based on age, weight, and/or BMI. For example, the gas flow may be decreased automatically by the HFT device to less than two times the patient expected tidal volume for five seconds every twelve breathing cycles. These types of periodic deviations from set gas flow rates could be inputted by the operator via the GUI or may be part of the programmed software. In an alternate embodiment, the HFT system may be used as a bubble CPAP system. The patient interface may have an expiratory tube connected to the nasal cannula portion for gas to exit. The distal end of the expiratory tube may be immersed in a water tank. In one embodiment, the water chamber may serve as the water tank. In an alternate embodiment, the water chamber may have a first water compartment that is fluidically coupled with the HFT device and the delivery circuit and a second water compartment that is fluidically coupled with the expiratory tube only and serves as the water tank. Water is placed in the water tank. The depth to which the expiratory tube is immersed underwater can determine the pressure generated in the airway of the patient. The gas flow may flow through the expiratory tube and bubble out into the water tank. The patient interface may be a sealed interface. The pressure sensing technology of the HFT system described throughout can be used to verify that the patient is receiving the desired pressure when the HFT system is being used as a bubble CPAP system or any embodiment described throughout. Automatic filling system technology described previously could be applied to the water tank.
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
