Patent Description:
<CIT> discloses a ventilator comprising a venturi tube which can be connected to the patient and has a proximal end and a distal end, high-pressure gas connections for breathing gases, a control device for setting ventilation parameters, and a device for dosing the ventilation gases, characterized in that the ventilation channel of a Venturi tube has an area with a variable cross section below an injector nozzle.

<CIT> discloses a device for respiratory assistance comprising a tube which forms a main channel, connected at a distal end to an airway of a patient so that the respiratory system is connected to the outside. At least one auxiliary channel is connected to a source of respirable gas to insufflate a jet of the gas into the respiratory system. Deflection means for the gas are also provided to create a pressure zone inside the main channel.

Throughout this specification the following non-SI units are used, which may be converted to the respective SI or metric unit according to the following conversion table:.

The invention in its various aspects is defined in the appended independent claims, to which reference should be made. Preferred features are set out in the dependent claims.

According to an aspect of the invention, there is provided a variable throat jet venturi according to claim <NUM>.

With the plenum in a first pressurization state, the variable throat jet venturi may achieve a pressure Pshutoff , with the gas outlet occluded, of at least <NUM> cmH<NUM>O at a jet nozzle pressure Pn of <NUM> psig and a jet nozzle flow V'n equal to or less than <NUM> slpm. With the plenum in a second pressurization state, the variable throat jet venturi may achieve a pressure Paw , with the gas outlet open, of <NUM> cmH<NUM>O at a jet nozzle flow V'n of less than <NUM> slpm, e.g. less than <NUM> slpm. With the plenum in the first pressurization state, a ratio At/An of a cross-sectional area of the deformable throat body to a cross-sectional area of the jet nozzle may be between <NUM> and <NUM>. With the plenum in the second pressurization state, the ratio At/An may be between <NUM> and <NUM>.

A distal tip of the jet nozzle may be outside the entrainment opening.

According to another aspect of the invention, there is provided a patient ventilation interface according to claim <NUM>. The nasal coupler may comprise a nasal pillow.

According to another aspect of the invention, there is provided a non-invasive ventilation system according to claim <NUM>. The non-invasive ventilation system may comprise a controller programmed to energize the pilot pressure line to constrict the deformable throat body during an exhalation phase of positive end-expiratory pressure (PEEP) therapy. The non-invasive ventilation system may comprise a multi-lumen tube having a ventilation gas lumen terminating in the nozzle and a pilot pressure lumen in fluid communication with the pilot pressure line.

According to another aspect of the invention, there is provided a method according to claim <NUM>.

The pressurizing of the plenum may include energizing a pilot pressure line fluidly coupled to a pilot pressure port defined by the housing.

The pressurizing of the plenum may comprise pressurizing the plenum from a first pressurization state, in which the variable throat jet venturi achieves a pressure Pshutoff , with the gas outlet occluded, of at least <NUM> cmH<NUM>O at a jet nozzle pressure Pn of <NUM> psig and a jet nozzle flow V'n equal to or less than <NUM> slpm, to a second pressurization state, in which the variable throat jet venturi achieves a pressure Paw , with the gas outlet open, of <NUM> cmH<NUM>O at a jet nozzle flow V'n of less than <NUM> slpm, e.g. less than <NUM> slpm. With the plenum in the first pressurization state, a ratio At/An of a cross-sectional area of the deformable throat body to a cross-sectional area of the jet nozzle may be between <NUM> and <NUM>. With the plenum in the second pressurization state, the ratio At/An may be between <NUM> and <NUM>.

The present disclosure encompasses various embodiments of a variable throat jet venturi for delivering ventilation gas to a patient, along with systems and methods for varying a ratio between a throat diameter and a jet nozzle diameter thereof. The detailed description set forth below in connection with the appended drawings is intended as a description of several currently contemplated embodiments and is not intended to represent the only form in which the disclosed invention may be developed or utilized. The description sets forth the functions and features in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions may be accomplished by different embodiments that are also intended to be encompassed within the scope of the present invention (provided they fall within the scope of the claims). It is further understood that the use of relational terms such as first and second and the like are used solely to distinguish one from another entity without necessarily requiring or implying any actual such relationship or order between such entities.

<FIG> shows an exemplary non-invasive ventilation system <NUM> according to an embodiment of the present disclosure, including a patient ventilation interface <NUM> that incorporates a variable throat jet venturi <NUM> for delivering ventilation gas to a patient. Due to the increased velocity of the ventilation gas at a constriction of the variable throat jet venturi <NUM>, there is a decrease in pressure that causes ambient air to be entrained via one or more entrainment ports <NUM>. By amplifying the ventilation gas output by a jet nozzle <NUM> in this way, the variable throat jet venturi <NUM> may serve as an efficient flow generator when providing ventilation therapy to the patient. Meanwhile, so that it may also serve as an efficient PEEP generator, the variable throat jet venturi <NUM> may include a deformable throat body <NUM> to serve as the constriction, with a housing <NUM> of the variable throat jet venturi <NUM> defining a pilot pressure port <NUM> for pressurizing a plenum <NUM> surrounding the deformable throat body <NUM> (e.g. via a feed and bleed circuit). By selectively pressurizing the plenum <NUM>, the plenum <NUM> can be transitioned between a first pressurization state for maximizing airflow to the patient (e.g. during inhalation) and a second pressurization state in which the deformable throat body <NUM> is more constricted. In the latter state, the reduced cross-sectional area of the deformable throat body <NUM> may significantly reduce the required nozzle flow for achieving a desired output pressure, making it possible to efficiently generate PEEP.

As shown by way of example in <FIG>, the patient ventilation interface <NUM> in which the variable throat jet venturi <NUM> is integrated may be a nasal interface having a pair of nasal couplers <NUM> (e.g. nasal pillows) for fluidly coupling a gas outlet of the deformable throat body <NUM> to the nostrils of the patient. Examples of such a nasal interface are described in <CIT>, entitled METHODS, SYSTEMS AND DEVICES FOR NON-INVASIVE VENTILATION INCLUDING A NON-SEALING VENTILATION INTERFACE WITH AN ENTRAINMENT PORT AND/OR PRESSURE FEATURE, <CIT>, entitled METHODS, SYSTEMS AND DEVICES FOR NON-INVASIVE OPEN VENTILATION WITH GAS DELIVERY NOZZLES IN FREE SPACE, <CIT>, entitled METHODS, SYSTEMS AND DEVICES FOR NON-INVASIVE VENTILATION INCLUDING A NON-SEALING VENTILATION INTERFACE WITH A FREE SPACE NOZZLE FEATURE, and <CIT>, entitled PATIENT INTERFACE WITH INTEGRATED JET PUMP. For example, the variable throat jet venturi <NUM> may be disposed within or constitute a manifold assembly <NUM> of the patient ventilation interface <NUM>, with the jet nozzle <NUM> integrated therewith or attachable to an end thereof. The manifold assembly <NUM> may be configured to fit between the patient's nose and upper lip and may serve to direct exit flow from the variable throat jet venturi <NUM> to the patient's nostrils.

With reference to <FIG>, it is contemplated that the variable throat jet venturi <NUM> may be integrated in or otherwise provided at one side of the manifold assembly <NUM> only, with the exit flow thereof being directed simultaneously to both of the patient's nostrils as shown. Along these lines, as indicated above, the manifold assembly <NUM> of the patient ventilation interface <NUM> may be outfitted with the spaced, identically configured pair of the nasal couplers <NUM> (e.g. nasal pillows) engageable to and placeable into fluid communication with respective ones of the patient's nostrils, and the manifold assembly <NUM> may place the variable throat jet venturi <NUM> into fluid communication with both such nasal couplers <NUM> by a single flow passage. Alternatively, the manifold <NUM> may define separate flow passages for each of the patient's left and right nostrils, in which case the variable throat jet venturi <NUM> and some or all of its features described herein may be duplicated for each side of the manifold <NUM>.

In order to provide for the pressurization of the plenum <NUM> as described above, the non-invasive ventilation system <NUM> includes a pilot pressure line <NUM> fluidly coupled to the pilot pressure port <NUM>. A controller <NUM> may be programmed to energize the pilot pressure line <NUM> to constrict the deformable throat body <NUM> during an exhalation phase of PEEP therapy. In the illustrated example, the non-invasive ventilation system <NUM> includes a multi-lumen tube <NUM> having a ventilation gas lumen <NUM> terminating in the jet nozzle <NUM> and a pilot pressure lumen <NUM> in fluid communication with the pilot pressure line <NUM>. The ventilation gas lumen <NUM> may receive ventilation gas from a ventilator or an oxygen concentrator, for example. The pilot pressure line <NUM> may extend from the multi-lumen tube <NUM> forward past the jet nozzle <NUM> to the pilot pressure port <NUM> of the variable throat jet venturi <NUM>.

Additional lumens of the multi-lumen tube <NUM> may include, for example, a low-pressure gas lumen for oxygen (which may terminate in a low-pressure jet nozzle outlet port near the jet nozzle <NUM>), a pressure sensing lumen (which may extend farther downstream to terminate nearer to the patient's nostril, such as at the base of the nasal coupler <NUM> closest the variable throat jet venturi <NUM> , for example), lumens for medicaments, etc. However, it is contemplated that in a preferred implementation, a second tube <NUM> may be provided which routes one or more of these lumens to the other side of the manifold assembly <NUM> (i.e., the side opposite that having the variable throat jet venturi <NUM> integrated therein). Such a pair of tubes <NUM> may branch upstream from a single multi-lumen tube using a wye connector such as that described in <CIT>. In <FIG>, for example, a second tube <NUM> is shown having, as its only lumen, a pressure sensing lumen <NUM> that extends to the base of one of the nasal couplers <NUM> in order to desirably measure pressure downstream of the variable throat jet venturi <NUM>. In this example, the first tube <NUM> will have no pressure sensing lumen. Along these lines, it is contemplated that any of the above-described lumens may be provided individually or in some prescribed combination at one or both sides of the interface <NUM> using the first tube <NUM> with or without the second tube <NUM>.

In a case where the non-invasive ventilation system <NUM> may include only a single multi-lumen tube <NUM> extending to the patient ventilation interface <NUM>, it is also contemplated that the multi-lumen tube <NUM> may interface with the manifold <NUM> at a central position equidistant from the nasal couplers <NUM>. For example, the multi-lumen tube <NUM> may connect to the manifold <NUM> between the nasal couplers <NUM> on the bottom or the front of the manifold <NUM> as viewed in <FIG>. In such case, this same central area, near the bases of the nasal couplers <NUM>, may house a single variable throat jet venturi <NUM> that is fed by the multi-lumen tube <NUM> and whose output flow is directed simultaneously to both nasal couplers <NUM>. As another possibility, the disclosed variable throat jet venturi <NUM> may be embodied in a detachable connector that interfaces the multi-lumen tube <NUM> with a mask or other patient interface at any appropriate position (and in some cases may be universally usable with multiple different patient interfaces). Examples of such connectors that can be equipped with the disclosed variable throat jet venturi <NUM> are the adaptors disclosed in <CIT>, entitled JET PUMP ADAPTOR FOR VENTILATION SYSTEM.

The controller <NUM> may be a standalone device dedicated to energizing the pilot pressure line <NUM> during PEEP therapy (e.g. based on sensor input indicative of an exhalation phase of a patient's breathing) or may be a controller of a ventilator or oxygen concentrator, for example. In this regard, exemplary ventilators and oxygen concentrators that may be used with the disclosed embodiments include, in addition to those mentioned above, those described in <CIT>, entitled MODULAR VENTILATION SYSTEM, <CIT>, entitled MODULAR VENTILATION SYSTEM, and <CIT> and entitled O2 CONCENTRATOR WITH SIEVE BED BYPASS AND CONTROL METHOD THEREOF". The controller <NUM> may energize the pilot pressure line <NUM> by controlling the pressure in the pilot pressure lumen <NUM> of the multi-lumen tube <NUM>, for example, by controlling a valve of a pilot pressure output port of a ventilator, oxygen concentrator, or other gas source that houses or is connected to the controller <NUM>.

<FIG> are cross-sectional views of the variable throat jet venturi <NUM> with the plenum <NUM> in the first pressurization state and the second pressurization state, respectively. <FIG> are additional perspective, exploded and exploded sectional views of the variable throat jet venturi <NUM>. As can be seen in <FIG>, when pressure increases in the plenum <NUM> (e.g. by activation of a pilot pressure line <NUM>, see <FIG>), the plenum <NUM> transitions from the first pressurization state (<FIG>) to the second pressurization state (<FIG>), with the buildup of pressure in the plenum <NUM> causing the deformable throat body <NUM> to become constricted. More specifically, a cross-sectional area At of the deformable throat body <NUM> (e.g. a smallest cross-sectional area corresponding to a diameter Dt in <FIG>) decreases from the first pressurization state to the second pressurization state. Given a nozzle having a fixed cross-sectional area An (corresponding to a diameter Dn), the ratio At/An thus decreases, reducing the required nozzle flow for achieving PEEP.

The deformable throat body <NUM> defines a gas inlet <NUM> and a gas outlet <NUM> and may have a generally tubular shape in its relaxed (e.g. as-molded) state as best shown in <FIG>. Flanges <NUM> may be defined at either end. Referring back to <FIG>, when the deformable throat body <NUM> is disposed within the housing <NUM>, the flanges <NUM> may function to position the deformable throat body <NUM> in a cavity defined therein. The flanges <NUM> may also serve to delineate a longitudinal extent of the plenum <NUM> between an outer wall <NUM> of the deformable throat body <NUM> and an inner wall <NUM> of the housing <NUM>. As the plenum <NUM> is pressurized as shown in <FIG>, the pressure may cause the deformable throat body <NUM> to constrict about its center while the flanges <NUM> remain firmly against the inner wall <NUM> of the housing <NUM> (with or without the use of adhesive). Thereafter, as the plenum <NUM> is depressurized, the deformable throat body <NUM> may return to its relaxed state as shown in <FIG>. The deformable throat body <NUM> may be a thermoplastic elastomer (TPE) or a thermoset produced by liquid injection molding (LIM) using liquid silicone rubber (LSR), for example.

The housing <NUM> may be assembled from one or more pieces <NUM>, <NUM> as shown, which may be attached to each other by ultrasonic welding, for example. The pieces <NUM>, <NUM> of the housing <NUM> may similarly be made of a thermoplastic or thermoset but may typically (but not necessarily) have greater rigidity than the deformable throat body <NUM>. In the illustrated example, there is an entry piece <NUM> and an exit piece <NUM>. In more detail, as shown in <FIG>, the entry piece <NUM> of the housing <NUM>, according to the invention, includes a generally frustoconical portion which flares outwardly away from the plenum <NUM> and defines an entrainment opening <NUM> open to ambient air. The exit piece <NUM> includes the inner wall <NUM> that defines the plenum <NUM>, and likewise includes a generally frustoconical portion which flares outwardly away from the plenum <NUM> and serves as a diffuser <NUM> that may provide the desired airflow and/or pressure to the patient, e.g. via the nasal couplers <NUM> (see <FIG>). According to the invention, the deformable throat body <NUM> receives the ventilation gas output by the jet nozzle <NUM> via the entrainment opening <NUM> of the housing <NUM>, in addition to ambient air which is drawn through the entrainment port <NUM> of the manifold assembly <NUM> and likewise introduced into the entrainment opening <NUM>. In this regard, as seen in <FIG>, the entrainment opening <NUM> (and hence the deformable throat body <NUM>) fluidly communicates with both the jet nozzle <NUM> and entrainment port <NUM> of the manifold assembly <NUM>. The distal tip of the jet nozzle <NUM> is outside the entrainment opening <NUM> as shown, with the entrainment of ambient air occurring around the periphery of the jet nozzle <NUM>.

In the implementation shown in <FIG> wherein the manifold assembly <NUM> includes the entrainment port <NUM> and the distal tip of the jet nozzle <NUM> is radially aligned with a portion of the entrainment port <NUM>, it is contemplated that the entrainment opening <NUM> may likewise be radially aligned with a portion of the entrainment port <NUM>, or located downstream therefrom.

The geometry of the variable throat jet venturi <NUM>, including the cross-sectional area of the nozzle <NUM> and in particular the geometry of the deformable throat body <NUM> when the plenum <NUM> is in the first and second pressurization states, may be selected to achieve desired performance characteristics. For purposes of illustration, maximum ventilator output capabilities may dictate a nozzle flow V'n ≤ <NUM> slpm and a nozzle pressure Pn = <NUM> psig, which, in turn, may limit the range of possible nozzle diameters. Using each of a plurality of possible nozzle diameters, candidate venturi geometries may be tested with the deformable throat body <NUM> in the relaxed state (plenum <NUM> in the first pressurization state as shown in <FIG>) to determine a shutoff pressure Pshutoff at the gas outlet <NUM> of the deformable throat body <NUM> and a maximum output flow V'aw-max at the maximum nozzle pressure Pn = <NUM>. In this way, it can be confirmed whether the candidate venturi geometry meets desired Pshutoff-V'aw-max performance. The same candidate venturi geometries may then be tested with the deformable throat body <NUM> in the constricted state (plenum <NUM> in the second pressurization state as shown in <FIG>) to determine the nozzle flow V'n needed to achieve PEEP, e.g. P'aw = <NUM> cmH<NUM>O, and the maximum output flow V'aw-max at that same nozzle flow V'n.

Exemplary data illustrating results of such a testing procedure is shown below in Tables <NUM> and <NUM>, for a first nozzle <NUM> having a nozzle diameter Dn = <NUM> inches (cross-sectional area An = <NUM> in<NUM>) and a second nozzle <NUM> having a nozzle diameter Dn = <NUM> inches (cross-sectional area An = <NUM> in<NUM>), respectively. In Tables <NUM> and <NUM>, the test numbers "#" are in the form "x. y" where x denotes different candidate venturi geometries <NUM>, <NUM>, <NUM>, and <NUM> and y denotes relaxed ("<NUM>") and constricted ("<NUM>") states of the deformable throat body <NUM> thereof, as depicted in <FIG>. The venturi geometries themselves are defined by a minimum cross-sectional diameter Dt (and minimum cross-sectional area At) of the deformable throat body <NUM>, a length Lt from the gas inlet <NUM> to the gas outlet <NUM> of the deformable throat body <NUM>, and a length Ld from the gas outlet <NUM> to the end of the diffuser <NUM>. In the example data of Tables <NUM> and <NUM>, the deformable throat body <NUM> is assumed to receive the ventilation gas output by the jet nozzle <NUM> through the entrainment opening <NUM> of the housing <NUM> as shown in <FIG>, with the length between the nozzle <NUM> and the gas inlet <NUM> of the deformable throat body <NUM> being <NUM> inches.

An exemplary test procedure for generating data like that of Tables <NUM> and <NUM> may be as follows for each test number "#". First, the gas outlet <NUM> (or the end of the diffuser <NUM>) is occluded and the nozzle flow V'n is increased until the outlet pressure Paw is equal to the target PEEP, e.g. Pshutoff = <NUM> cmH2O. The nozzle flow V'n and nozzle pressure Pn are recorded in the first row. The gas outlet <NUM> is then opened and the outlet pressure Paw and output flow V'aw are recorded in the same row. Next, the nozzle pressure Pn is set to the target maximum <NUM> psig. The nozzle flow V'n, outlet pressure P'aw, and output flow V'aw are now recorded in the second row. Lastly, the gas outlet <NUM> is again occluded, and the shutoff pressure Pshutoff corresponding to the maximum nozzle flow V'n is recorded in the second row. The procedure can be repeated for different nozzles and candidate venturi geometries with the deformable throat body <NUM> in both relaxed and constricted states (corresponding to the first and second states of the plenum <NUM> shown in <FIG>).

To calculate the maximum output flow V'aw-max, the measured output flow V'aw taken at the target maximum nozzle pressure Pn of <NUM> psig can be multiplied by the corresponding shutoff pressure Pshutoff and divided by the difference between the shutoff pressure Pshutoff and the corresponding measured outlet pressure P'aw, as follows: V'aw-max = V'aw * Pshutoff / (Pshutoff - Paw). The ratio Xmax of the maximum output flow V'aw-max to the maximum nozzle flow V'n can be calculated as follows: Xmax = V'aw-max / V'n.

The performance characteristics of interest can then be tabulated from the combined data of the relaxed and constricted states of the deformable throat body <NUM> of each candidate venturi geometry, as summarized in Tables <NUM> and <NUM> below for nozzle diameters Dn = <NUM> inches and Dn = <NUM> inches, respectively:.

An exemplary venturi geometry that achieves desired performance characteristics is shown in Table <NUM>, below, with unused data omitted, for a nozzle <NUM> having a nozzle diameter Dn = <NUM> inches (cross-sectional area An = <NUM> in<NUM>). Again, the deformable throat body <NUM> is assumed to receive the ventilation gas output by the jet nozzle <NUM> through the entrainment opening <NUM> of the housing <NUM> as shown in <FIG>, with the length between the nozzle <NUM> and the gas inlet <NUM> of the deformable throat body <NUM> being <NUM> inches.

The tabulated performance characteristics of interest from the combined data of the relaxed and constricted states of the deformable throat body <NUM> of the above candidate venturi geometry #<NUM> are summarized in Table <NUM> below:.

As can be seen from Tables <NUM> and <NUM> (and as graphically depicted in <FIG>), a variable throat jet venturi <NUM> having candidate venturi geometry #<NUM> achieves a shutoff pressure Pshutoff at the gas outlet <NUM> of <NUM> cmH<NUM>O (meeting target performance characteristics of at least <NUM> cmH<NUM><NUM>) at a jet nozzle pressure Pn of <NUM> psig and a jet nozzle flow V'n of <NUM> lpm (which is less than or equal to <NUM> slpm) while the plenum <NUM> is in a first pressurization state (uninflated) corresponding to the relaxed state of the deformable throat body <NUM>. A maximum output flow V'aw-max = <NUM> is achieved. Meanwhile, when the plenum <NUM> is in a second pressurization state (inflated) corresponding to the constricted state of the deformable throat body <NUM>, the same variable throat jet venturi <NUM> achieves PEEP (gas outlet pressure Paw = <NUM> cmH<NUM>O) at a jet nozzle flow V'n of <NUM> slpm. Thus, using a variable throat jet venturi <NUM> having a deformable throat body <NUM> as described herein, PEEP (e.g. gas outlet pressure Paw = <NUM> cmH<NUM>O) can be achieved at a jet nozzle flow V'n of less than <NUM> slpm, which is less than half of the <NUM> slpm that is typically required with conventional NIOV devices and, in some cases, at a jet nozzle flow V'n of less than <NUM> slpm, which is less than a quarter of typical requirements. It is worth noting, however, that energizing a pilot pressure line <NUM> as used in some implementations of the disclosed deformable throat body <NUM> may use some airflow, e.g. <NUM> slpm.

Equivalent testing can be performed to select a venturi geometry that meets design constraints of any patient interface <NUM>, for example, one in which one or more entrainment openings <NUM> have a side-by-side relationship with the jet nozzle <NUM> and/or for different lengths between the nozzle <NUM> and the gas inlet <NUM> of the deformable throat body <NUM>. Along the same lines, the venturi geometry can be selected to meet different performance characteristics, including different maximum ventilator output capabilities other than nozzle flow V'n ≤ <NUM> slpm and nozzle pressure Pn = <NUM> psig, different PEEP other than <NUM> mmH<NUM>O, different target shutoff pressure Pshutoff and maximum output flow V'aw-max at the maximum nozzle pressure Pn, etc..

The controller <NUM> of the non-invasive ventilation system <NUM> (which may be a controller of an oxygen concentrator or ventilator as noted above) may be implemented with a programmable integrated circuit device such as a microcontroller or control processor. Broadly, the device may receive certain inputs, and based upon those inputs, may generate certain outputs. The specific operations that are performed on the inputs may be programmed as instructions that are executed by the control processor. In this regard, the device may include an arithmetic/logic unit (ALU), various registers, and input/output ports. External memory such as EEPROM (electrically erasable/programmable read only memory) may be connected to the device for permanent storage and retrieval of program instructions, and there may also be an internal random access memory (RAM). Computer programs for implementing any of the disclosed functionality of the controller <NUM> may reside on such non-transitory program storage media, as well as on removable non-transitory program storage media such as a semiconductor memory (e.g. IC card), for example, in the case of providing an update to an existing device. Examples of program instructions stored on a program storage medium or computer-readable medium may include, in addition to code executable by a processor, state information for execution by programmable circuitry such as a field-programmable gate arrays (FPGA) or programmable logic device (PLD).

In the above examples, a variable throat jet venturi <NUM> is implemented with a deformable throat body <NUM> whose cross-sectional area At is selectively changed relative to a fixed cross-sectional area An of a jet nozzle <NUM>. However, it is also contemplated that the cross-sectional area An of the jet nozzle <NUM> may itself be selectively decreased or increase instead of or in addition to the cross-sectional area At of a deformable throat body <NUM>. For example, the cross-sectional area An of the jet nozzle <NUM> may be selectively changed by translating a tapered pin axially along the nozzle <NUM> or pressurizing an inflatable bladder similar to the plenum <NUM> described above. As another possibility, two jet nozzles <NUM> may be used, one for achieving PEEP at low nozzle flow V'n and the other for achieving desired Pshutoff-V'aw-max performance. Exemplary data of candidate jet nozzle diameters Dt for use with the disclosed embodiments is shown in Table <NUM>, below:.

For ease of explanation, the above disclosure assumes that the variable throat jet venturi <NUM> has a single jet nozzle <NUM>. As such, the cross-sectional area An is described as corresponding to the diameter Dn of the jet nozzle <NUM>. However, the disclosure is not limited in this regard. For example, the variable throat jet venturi <NUM> may include a plurality of jet nozzles <NUM> arranged in a ring or other pattern. In this case, the cross-sectional area An may refer to the total cross-sectional area of the plurality of jet nozzles <NUM> for purposes of evaluating the ratio At/An.

Claim 1:
A variable throat jet venturi (<NUM>) for delivering ventilation gas to a patient, the variable throat jet venturi (<NUM>) comprising:
a jet nozzle (<NUM>);
a deformable throat body (<NUM>) arranged to receive ventilation gas output by the jet nozzle (<NUM>) and defining a gas inlet (<NUM>) and a gas outlet (<NUM>); and
a housing (<NUM>) containing the deformable throat body (<NUM>), the housing (<NUM>) defining a pilot pressure port (<NUM>) for pressurizing a plenum (<NUM>) between an outer wall (<NUM>) of the deformable throat body (<NUM>) and an inner wall (<NUM>) of the housing (<NUM>),
characterised in that the housing (<NUM>) has a frustoconical portion that flares outwardly away from the plenum (<NUM>) and defines an entrainment opening (<NUM>) which is open to ambient air, and in that the deformable throat body (<NUM>) is arranged to receive the ventilation gas output by the jet nozzle (<NUM>) through the entrainment opening (<NUM>) of the housing (<NUM>).