GB2593586A

GB2593586A - Air flow system

Info

Publication number: GB2593586A
Application number: GB2101893.2A
Authority: GB
Inventors: John Beckett Oliver
Original assignee: Johnson Matthey PLC
Current assignee: Johnson Matthey PLC
Priority date: 2020-03-27
Filing date: 2021-02-11
Publication date: 2021-09-29
Also published as: GB202101893D0; WO2021191580A1; GB202004482D0

Abstract

A ventilator system to aid human or animal respiration comprising a cylinder 3 orientated in a substantially vertical direction; a piston 4 disposed within the cylinder and slidable up and down the cylinder to provide an upstroke and a downstroke respectively; and a drive coupling 19 configured to be connected to a drive mechanism to drive the upstroke of the piston by drawing the piston up the cylinder. A control system is configured to release the piston at the top of the upstroke, allowing the piston to fall down the cylinder under its own weight such that air is forced out of the cylinder below the piston through an outlet 13. The control system then re-engages the drive mechanism at the bottom of the downstroke to drive the upstroke of the piston and draw air into the cylinder below the piston from outside the cylinder, wherein the piston has a size and weight sufficient to drive the downstroke under gravity, or is biased by a spring, delivering air to the patient. The drive mechanism may be a suction device whose connection to the cylinder may be selectively engaged using valves.

Description

AIR FLOW SYSTEM

Field

The present specification relates to an air flow system and particularly to a ventilator system to aid human respiration in the event of respiratory illness. This may be as a result of acute respiratory distress syndrome (ARDS) or in the event of any other medical condition where a patient is struggling to breath unaided. The present specification is particularly directed to a simplified, optionally portable, ventilator system to aid human respiration in the situation where more complex ventilator systems are not available and where continuous respiratory ventilation may be required over a prolonged time period such that manually operated respirator systems are not suitable.

Background

Respirator systems are a well-known for use in aiding human respiration in the event of a medical condition which results in a patient struggling to breath unaided.

Respirator systems are usually located within a hospital environment and comprise a dedicated power supply configured to power an electro-mechanical device for providing a regular, periodic air flow to a patient's lungs to mimic the air flow into a person's lungs under normal breathing conditions.

Portable respiratory systems are also known in the art for use in the field. These can be manually operated devices. For example, they may comprise a mouth-piece for placing over a patient's mouth and a compressible bulb made of a resilient material which can be squeezed by a paramedic to compress the bulb and force air into the patient's lungs and then released to enable air to flow out of the patient's lungs. Since such simple respirator systems require continual manual operation, they are only intended for temporary use until the patient can be transferred to a powered respirator system.

Battery powered portable respirator systems are also known in the art. However, these are relatively complex systems with a dedicated electrical power supply system.

In certain circumstances, complex ventilator systems may not be available. This may be the case, for example, in remote environments, poor countries, or in the event of extreme medical emergencies when the number of patients exceeds the number of available respirators, e.g. in an epidemic or global pandemic which causes respiratory problems in a large number of people.

Another related problem is that known ventilator systems can be complex, time consuming, and/or expensive to manufacture. In this regard, 3D printing techniques are known for manufacturing complex devices. However, the complexity of the device can slow the 3D printing process. The rate limiting step for 3D printing a ventilator is that a complex drive control system is required for powering the device.

The present specification describes a solution to the aforementioned problem.

Summary

The present specification provides a ventilator system to aid human or animal respiration comprising: a cylinder orientated in a substantially vertical direction with a top end and a bottom end; a piston disposed within the cylinder and slidable up and down the cylinder to provide an upstroke and a downstroke respectively; a drive coupling configured to be connected to a drive mechanism to drive the upstroke of the piston by drawing the piston up the cylinder; a control system configured to release the piston at the top of the upstroke enabling the piston to move down the cylinder under its own weight for the downstroke such that during the downstroke of the piston air is forced out of the cylinder below the piston through an outlet coupling and into the patient's lungs, the control system being configured to re-engage the drive mechanism at the bottom of the downstroke to drive the upstroke of the piston and draw air into the cylinder below the piston from outside the cylinder, wherein the piston has a size and weight sufficient to drive the downstroke delivering air to the patient on the downstroke.

Such a ventilator system is based on a vertically orientated, weighted free piston concept in which the weight of the piston drives the air flow to a patient on a downstroke of the piston and a drive mechanism lifts the weighted piston on an upstroke. A control system in the form of a valve, switching, latching or coupling system is provided in order to couple and de-couple the drive mechanism and the piston in a periodic manner to switch between upstroke and downstroke at a rate which mimics the breathing rate of a patient.

Such a weighted free piston ventilator configuration can have one or more of the advantages as outlined below.

First, it can readily be coupled to a variety of drive mechanisms. For example, in one configuration the ventilator system can be couple to a standard domestic vacuum cleaner as the drive mechanism with suction from the vacuum cleaner raising the piston and a valve system releasing the suction at the top of the upstroke thus enabling the piston to fall downwards under its own weight for the downstroke. The valve system can be configured to move back to the suction position at the bottom of the downstroke such that the piston is then sucked back up the piston cylinder. As vacuum cleaner devices are ubiquitous, such a ventilator system can be utilized in the field without the requirement for a dedicated power source. Alternatively, the drive mechanism can be a mechanical drive mechanism. Alternatively still, the drive mechanism may be a manually actuated drive mechanism.

Secondly, the configuration is inherently safe for the patient. The maximum pressure of air which can be delivered to a patient is limited by the weight of the piston. The system is not reliant on regulating a high-pressure air flow in a direction towards the patient, which could be hazardous in the event of a failure in the air flow regulating system. Furthermore, the pressure and volume of air delivered to the patient is not reliant on the specific power of the drive mechanism but rather is controlled only by the size and weight of the piston. As such, the ventilator system can be driven off a range of driving mechanisms with varying power ratings without any variation in the flow pressure and volume delivered to the patient.

Thirdly, the system is simple, quick, and cheap to manufacture and does not require complex parts made to precise tolerances.

Fourthly, while the system can be actuated and controlled using electrical components, it is also possible to provide a purely mechanical ventilator system using the weighted free piston concept. As such, the system can be manufactured easily and quickly, e.g. using 3D printing techniques. Furthermore, the system can be made to be robust without delicate parts which could be damaged during transport and use. Further still, the system can be used in a variety of environments including outdoors and in wet conditions without problems of electrical faults.

Fifthly, it is simple to adjust the weight of the piston and/or limit the stroke length of the piston and/or include one or more flow regulators in the air flow path to a patient to provide a variety of pressures, tidal volumes, and cadence rates to suit a range of human/animal patient requirements.

The ventilator systems as described herein can be used to aid respiration of a human or animal patient in medical and veterinary applications. A method of aiding human or animal respiration is thus provided, the method comprising: coupling a ventilator system as described herein to the airway of a human or animal patient; and operating the ventilator system to deliver air to the patient to aid respiration.

While the aforementioned ventilator systems are based on a vertically orientated, weighted free piston concept, it is also envisaged that other configurations could be provided which are powered off a continuous suction device such as a domestic vacuum cleaner. It is also envisaged that the ventilator systems as described herein may be configured to be operated off a blowing device rather than a suction device. For example, a blowing device can be coupled to a vertically orientated, weighted free piston with the system re-configured such that air is blown into the cylinder below the piston to raise the piston and then de-coupled to enable the piston to drop to deliver the air to the patient. Further still, the ventilator systems as described herein may be powered by a mechanical drive mechanism rather than a suction or blowing device. For example, a mechanical drive mechanism may be provided for a vertically orientated, weighted free piston system which is re-configured such that piston is mechanical lifted (rather than sucked upwards or blown upwards) and then released to enable the piston to drop to deliver air to the patient.

In another configuration a ventilator system may be based on a biased piston concept rather than a weighted free piston concept while still retaining several of the benefits as described above. For example, a ventilator system can be provided to aid human or animal respiration comprising: a cylinder; a piston disposed within the cylinder and slidable along the cylinder to provide an outstroke and an instroke respectively; a drive coupling configured to be connected to a drive mechanism to drive the outstroke of the piston by drawing the piston along the cylinder; a biasing means, such as a spring or equivalent, to bias the piston to drive the instroke; and a control system configured to release the piston at the end of the outstroke enabling the piston to move along the cylinder under biasing force from the biasing means for the instroke such that during the instroke of the piston air is forced out of the cylinder through an outlet coupling and into the patient's lungs, the control system being configured to re-engage the drive mechanism at the end of the instroke to drive the outstroke of the piston and draw air into the cylinder from outside the cylinder, wherein the biasing means generates sufficient force to drive the instroke delivering air to the patient on the instroke.

In this arrangement, the biasing means drives air delivery rather than the weight of the piston. The configuration still has the advantage that the pressure and volume of air delivered to the patient is controlled by the configuration of the system and not the power of the drive mechanism. As such, operational parameters such as pressure, volume and cadence can be safely selected and controlled by selection of a suitable biasing means and selection of a piston configuration having a piston size, weight, and stroke length to achieve the desired air delivery.

Brief Description of the Drawings

For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a schematic cross-sectional view of the core components of a ventilator system according to one embodiment described herein; and Figure 2 shows another schematic cross-sectional view of the ventilator system, orientated at a 900 angle relative to the cross-sectional view shown in Figure 1.

It is to be noted that the illustrated embodiment is just one example of a configuration implementing the inventive concepts as described herein and it is possible to implement the invention in a variety of different ways. For example, while a particular valve system configuration is illustrated, the required functionality of the valve system can be achieved using a variety of mechanical or electromechanical configurations based on conventional engineering components.

Detailed Description

As described in the summary section, in accordance with one configuration the present specification provides a ventilator system based on a vertically orientated, weighted free piston concept in which the weight of the piston drives the air flow to a patient on a downstroke of the piston and a drive mechanism lifts the weighted piston on an upstroke. Such a ventilator system comprises: a cylinder orientated in a substantially vertical direction with a top end and a bottom end; a piston disposed within the cylinder and slidable up and down the cylinder to provide an upstroke and a downstroke respectively; a drive coupling configured to be connected to a drive mechanism to drive the upstroke of the piston by drawing the piston up the cylinder; a control system configured to release the piston at the top of the upstroke enabling the piston to move down the cylinder under its own weight for the downstroke such that during the downstroke of the piston air is forced out of the cylinder below the piston through an outlet coupling and into the patient's lungs, the control system being configured to re-engage the drive mechanism at the bottom of the downstroke to drive the upstroke of the piston and draw air into the cylinder below the piston from outside the cylinder, wherein the piston has a size and weight sufficient to drive the downstroke delivering air to the patient on the downstroke.

It should be noted that the cylinder and piston arrangement is not necessarily required to be orientated in a precisely vertical fashion. For example, the cylinder may be oriented within an angle of +/-450, 350, 25°, 15°, 100, or 5° to vertical. It is sufficient that the orientation is such as to allow the piston to fall under its own weight in this example. Indeed, in certain configurations tilting the cylinder and piston orientation can be used as a means of moderating the output pressure of the system. As such, in certain configurations the system may comprise a tilting mechanism for controllably tilting the orientation of the piston and cylinder configuration.

The drive mechanism can be an integral part of the ventilator system. For example, the drive mechanism may be housed within the ventilator system in a common housing with the cylinder and piston components. Alternatively, the drive mechanism can be a separate device which is detachably couplable to the drive coupling of the ventilator system, e.g. a domestic vacuum cleaner, industrial suction pump, hair dryer, or other air flow or mechanical driving device.

In one configuration, the drive mechanism is a suction device (e.g. a vacuum cleaner) and the drive coupling is configured to be connected to the suction device to drive the upstroke of the piston by sucking air out of the cylinder above the piston thus drawing the piston up the cylinder. In this configuration, the control system may comprise a valve system which is configured to couple suction from the suction device to the piston to drive the upstroke of the piston and decouple suction from the piston enabling the piston to move down the cylinder under its own weight for the downstroke. The piston has a size and weight such that the suction from the suction device is sufficient to drive the upstroke and the weight of the piston is sufficient to drive the downstroke delivering air to the patient on the downstroke.

The suction device may be configured to provide a continuous suction to the drive coupling and the valve system is configured to couple the continuous suction from the suction device to the piston to drive the upstroke of the piston and then release the piston from the continuous suction of the suction device such that the piston is free to move down the cylinder under its own weight for the downstroke. In an alternative arrangement, the suction device may be configured to turn on and off the suction to the drive coupling.

The control system can be a mechanically actuated control system or may comprise an electrical switching system. The control system can be configured to be actuated by the piston at the bottom of the downstroke to engage the drive mechanism and configured to be actuated by the piston at the top of the upstroke to disengage the drive mechanism.

The ventilator system can be configured such that the cylinder comprises two one-way ports located below the piston including a first one-way port which enables air to flow out of the cylinder during the downstroke to the patient and a second one-way port which enables air to flow into the cylinder below the piston during the upstroke. Furthermore, the cylinder may comprise a port located above the piston which enables air to flow into the cylinder above the piston during the downstroke thus allowing the piston to move down the cylinder under its own weight during the downstroke without generating a negative pressure above the piston which would otherwise impede the downward motion of the piston. In this configuration, and when a suction device is used to raise the piston, the control system is configured to close the upper port during the upstroke thus sealing the upper chamber of the cylinder above the piston to enable the suction device to suck the piston up the cylinder. The control device is then configured to open the upper port during the downstroke. In this configuration, the cylinder thus comprises at least two upper ports: one connected to the suction device; and another connecting to outside the cylinder allowing air to flow in to reduce or eliminate the pressure differential on the piston and allowing the piston to drop down the cylinder.

The system components are configured to achieve operational parameters suitable for aiding respiration of a human or animal patient. For example, the size and weight of the piston is selected to generate an outlet air pressure in a range 50 to 1000 mm of water. The outlet air pressure may be: at least 50, 100, 200, or 250 mm of water; no more than 1000, 800, 600, or 400 mm of water; or within a range defined by any combination of the aforementioned lower and upper limits.

The size of the cylinder and the stroke length of the piston can be selected to deliver a volume of air to the patient on the downstroke in a range 50 ml to 1.5 litres. The volume of air delivered to the patient may be: at least 50, 100, 200, 300, 400, or 500 ml; no more than 1500, 1000, 800, or 700 ml; or within a range defined by any combination of the aforementioned lower and upper limits.

The size of the cylinder and the stroke length of the piston can selected to deliver a volume of air to the patient on the downstroke in a range 1 to 15 ml per Kg body weight of the patient. The volume of air delivered to the patient may be: at least 1, 2, 3,4, or 5 ml per Kg body weight of the patient; no more than 15, 10, 8, or 7 ml per Kg body weight of the patient; or within a range defined by any combination of the aforementioned lower and upper limits.

The ventilator system can be configured to have a cadence in a range 5 to 40 breaths per minute. The ventilator system can have a cadence of: at least 5, 8, 10 or 12 breaths per minute; no more than 40, 30, 25, or 20 breaths per minute; or within a range defined by any combination of the aforementioned lower and upper limits.

It may be noted that while the aforementioned values are typical for human patients, the values may differ for use on various different animals in veterinary applications.

Further still, a single drive mechanism can be provided for each ventilator or alternatively more than one ventilator can be coupled to a single drive mechanism.

Figures land 2 show cross-sectional views of an example of such a ventilator system. In the Figures, parts are labelled according to the following key: 1. Vacuum Valve Housing 2. Vacuum Valve 3. Cylinder Body 4. Piston 5. Piston Sealing Rings 6. Valve Actuator 7. Breathing Air Valve Housing 8. Valve Actuator Tie Rod 9. Sealing Rings -all small black circles (optional) 10. Valve Retaining Plate 11. Magnet 12. Magnet Anchor 13. Breathing Air Output Port 14. One-way Valve Plate 15. One-way Valve Seal 16. Breathing Air Inlet Port 17. Atmospheric Air Port 18. Vacuum Port (Low pressure air, not actually vacuum) 19. Optional Additional Port -Vents vacuum port to atmosphere as well as cylinder top.

A weighted free piston 4 is placed in an air filled, vertically orientated, open ended cylinder 3. The piston 4 is sealed against the cylinder walls 3 with relatively low friction seals S. If the pressure above the piston is lowered such that the pressure differential causes a net force on the piston exceeding its weight, the piston will rise against gravity. If the pressures above and below the piston are allowed to equalize, the piston will fall under its own weight, driving air out through the bottom of the cylinder. If air flow out of the bottom of the cylinder is restricted, the air below the piston will reach a maximum gauge pressure of Piston weight / Piston Cross Sectional Area.

At the top of the cylinder there is provided a vacuum valve housing 1 including a vacuum valve 2. By vacuum we don't require an absolute vacuum but rather a pressure reduction causing suction of the piston up the cylinder. The vacuum valve housing 1 includes an atmospheric air port 17 for releasing pressure for the downstroke and a vacuum port 18 (Low pressure air, not actually vacuum) for connection to the suction device. There may also be provided an optional additional port 19 which vents the vacuum port to atmosphere or to the cylinder top depending on position.

Also provided at the top of the cylinder are valve retaining plate 10, a magnet 11, and a magnet anchor 12. These components function to hold the vacuum valve 2 in position during the downstroke of the piston with the atmospheric air port 17 open.

At the lower end of the cylinder is a valve actuator 6 which is actuated by the piston at the bottom of its downstoke. A valve actuator tie rod 8 pulls down on the vacuum valve 2 switching to close the atmospheric air port 17 and engage suction through the vacuum port 18 to raise the piston. Part 7 is the breathing air valve housing with sealing rings 9 disposed around various parts of the apparatus for sealing (these are optional depending on the precision and fit of the components.

Also located at the bottom end of the cylinder are breathing air output port 13 (to patient on downstroke), breathing air inlet port 16 (for drawing air in on the upstroke) and one-way valve plate 14 and one-way valve seal 15 for ensuring that ports 13 and 16 function in one direction only as required.

The World Health Organization (WHO) recommend a pressure of 300 mm of H20 equivalent to support patients with Acute Respiratory Distress Syndrome. Continuous positive airway pressure (CPAP) machines typically operate at around 100 mm H2O equivalent pressure. In the ventilator system of the present specification, the air pressure may be moderated by adjusting the weight of the piston or using a pressure modulator to suit the patient and the condition being treated. Ventilators are typically set to a "tidal volume" of 5-7m1 per kg of ideal body weight, although this may be altered to suit the patient and the condition. For example, a simple adjustable stopper system can be located within the cylinder to limit the stroke length of the piston and thus adjust the tidal volume of air.

The bottom of the cylinder may be capped off and a pair of opposing one-way valves sealed into openings in the cap. If the pressure above the piston is alternated between "low" and atmospheric pressure, the piston will repeatedly rise and fall. As the piston rises, it will draw air into the bottom of the cylinder from outside through one of the one-way valves. As the piston it falls it will push air out through the other of the one-way valves towards the patient. The volume of air drawn in and pushed out of the cylinder will be proportional to the travel distance of the piston. The air above the piston may also be controlled to be above or below atmospheric pressure to moderate output pressure. A breathing circuit may be connected to the air out port to allow a patient to be ventilated by such a device. Additional gases may be fed into the intake port, or directly into the breathing loop to modify the gas mixture received by the patient. As such, while the present specification refers to air flow, the term "air" should not be interpreted to be limited to only the standard gas composition of air, but rather should be understood to include modified gas compositions. For example, additional oxygen may be incorporated into the gas mixture to aid the patient. Other gases may alternatively or additionally be introduced such as nitrous oxide to alleviate pain.

An additional valve may be configured to control the pressure at the top of the cylinder, switching between a supply of low-pressure air and one of atmospheric pressure. If this valve is switched to low pressure when the piston is at, or near to, the bottom of its stroke and to atmospheric at the top, the piston will cycle between the top and bottom of the cylinder. Valve actuation may be performed mechanically or electromechanically by means of sensors and actuators, solenoids motors, etc.. Alternatively, this effect may also be achieved by switching on and off a vacuum pump or other supply accordingly.

In the case that the valve is electronically controlled, the ventilator may be configured to support a breathing patient, by releasing the piston when a drop in pressure due to the patient inhaling is detected at the intake port or in the breathing circuit.

The cadence or cycle time for the ventilator system is controlled by a number of factors. During the upstroke the acceleration, maximum velocity, and therefore upstroke time, are determined by low pressure supply pressure, low pressure flow rate, and air inlet flow rate. During the downstroke the acceleration, maximum velocity, and therefore downstroke time, are determined by a combination of, atmospheric pressure port flow rate, and air outlet flow rate. Additionally, "dwell time" may be created at the stroke ends by introducing a time delay. Cadence = 1 / cycle time. The aforementioned variables may be readily adjusted individually or collectively to control breathing rate. A typical ventilator cadence range is 12-20 breaths per minute. A pulse oximeter or similar device may be used to measure the patient's blood oxygen concentration and used in a feedback loop to control cadence or additional gas supply.

A ventilator system as described herein may be powered as an individual stand-alone system, e.g. by a vacuum pump such as a vacuum cleaner or industrial vacuum pump. Alternatively, several (two or more) ventilators may be powered from a single power source. In this case a manifold can be provided to link two or more ventilator systems to a single power source. For example, a vacuum pump may be coupled to more than one ventilator. The example described herein is such that at least two systems can be powered by a single domestic vacuum cleaner.

As previously described, a vacuum (suction) lifts a free piston, drawing air into the bottom of the cylinder. When the piston gets to the top, it actuates a valve which closes the vacuum port and opens an air port. The piston then falls under its own weight, driving air out of the bottom of the piston through a one-way valve into a breathing loop. At the bottom of its stroke, the piston opens the vacuum valve and is lifted back up. Pressure is set by piston weight, tidal volume is set by stroke length, and cadence is controlled by several factors including vacuum/suction level.

Sensing the piston position is not necessary but can be desirable in certain configurations. For example, a simple switching system can be provided which switched the driving mechanism (e.g. suction device) on and off at set intervals. Furthermore, additional sensors can be provided to monitor performance. For example, to monitor to confirm that the system is working as desired, a pressure sensor can be provided to measure output air pressure.

It is also envisaged that air flow can be moderated. For example, vacuum/suction can be moderated either by partially occluding (obstructing/closing) the suction pipework or by opening a hole in the suction pipework or upper portion of the cylinder.

Dimensions of the various components can be varied. The illustrated embodiment was constructed using a cylinder having an outer diameter of 68 mm and an inner diameter in a range 64.3 -65.1 mm. Cross-sectional area = 6.52*pi/4 = 33.2 cm2. Assuming 100% efficiency, tidal volume is 33.2 cm3 per 1 cm of stroke, and can be adjusted to suit the patient. As previously indicated, guidelines suggest 5-7 ml tidal volume per kg of ideal body weight. For example, an 80 kg man might require 560 ml tidal volume. The WHO suggest treating ARDS with pressure of 300 mm of H20. Pressure is set by the weight of the piston, with 300mm of H20 equating to 996g assuming no friction (so the weight needs to be adjusted upwards to account for friction). The piston seals don't have to be perfect, but they do have to be low friction.

While the aforementioned ventilator system is based on a vertically orientated, weighted free piston concept, an alternative configuration provides a ventilator system based on a biased piston. Such a ventilator system comprises: a cylinder; a piston disposed within the cylinder and slidable along the cylinder to provide an outstroke and an instroke respectively; a drive coupling configured to be connected to a drive mechanism to drive the outstroke of the piston by drawing the piston along the cylinder; a biasing means, such as a spring or equivalent, to bias the piston to drive the instroke; and a control system configured to release the piston at the end of the outstroke enabling the piston to move along the cylinder under biasing force from the biasing means for the instroke such that during the instroke of the piston air is forced out of the cylinder through an outlet coupling and into the patient's lungs, the control system being configured to re-engage the drive mechanism at the end of the instroke to drive the outstroke of the piston and draw air into the cylinder from outside the cylinder, wherein the biasing means generates sufficient force to drive the instroke delivering air to the patient on the instroke.

In this arrangement, the biasing means drives air delivery rather than the weight of the piston. The configuration still has the advantage that the pressure and volume of air delivered to the patient is controlled by the configuration of the system and not the power of the drive mechanism. As such, operational parameters such as pressure, volume and cadence can be safely selected and controlled by selection of a suitable biasing means and selection of a piston configuration having a piston size, weight, and stroke length to achieve the desired air delivery. Aspects of the previously described system can also be applied to this biased piston system. It is also envisaged that elements of both systems may be combined. For example, a vertical configuration may be provided with a biasing means such that the piston drives the air flow by a combination of weight and biasing force.

Alternatively still, in another arrangement the direction of the drive mechanism and biasing means can be reversed so that the drive mechanism drives the instroke and the biasing means drives the outstroke. This has the advantage that the air parameters (pressure, volume) delivered to the patient can be controlled by controlling the drive mechanism. However, this arrangement will be more sensitive to variations in the power of the drive mechanism and so will depend on the reliability of the drive mechanism to deliver the desired power.

Alternatively, or additionally, the drive mechanism may be a manually actuated drive mechanism. In this case, manual actuation can be used to drive the upstroke or outstroke with the piston weight or biasing means used to provide a controlled instroke/downstroke to controllably deliver air to a patient with the correct pressure and volume.

The simplicity and flexibility of the presently described systems enable fast manufacturing design, tooling, and scale-up. Furthermore, the systems are inherently safe, robust, and ideally suited for use in field hospitals, hotel rooms, etc. in the event that hospitals run out of beds and ventilators.

While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Claims 1. A ventilator system to aid human or animal respiration comprising: a cylinder orientated in a substantially vertical direction with a top end and a bottom end; a piston disposed within the cylinder and slidable up and down the cylinder to provide an upstroke and a downstroke respectively; a drive coupling configured to be connected to a drive mechanism to drive the upstroke of the piston by drawing the piston up the cylinder; a control system configured to release the piston at the top of the upstroke enabling the piston to move down the cylinder under its own weight for the downstroke such that during the downstroke of the piston air is forced out of the cylinder below the piston through an outlet coupling and into the patient's lungs, the control system being configured to re-engage the drive mechanism at the bottom of the downstroke to drive the upstroke of the piston and draw air into the cylinder below the piston from outside the cylinder, wherein the piston has a size and weight sufficient to drive the downstroke delivering air to the patient on the downstroke.
2. A ventilator system according to claim 1, wherein the drive mechanism is an integral part of the ventilator system.
3. A ventilator system according to claim 1, wherein the drive mechanism is a separate device which is detachably couplable to the drive coupling of the ventilator system.
4. A ventilator system according to any preceding claim, wherein the drive mechanism is a suction device and the drive coupling is configured to be connected to the suction device to drive the upstroke of the piston by sucking air out of the cylinder above the piston thus drawing the piston up the cylinder, and the control system comprises a valve system which is configured to couple suction from the suction device to the piston to drive the upstroke of the piston and decouple suction from the piston enabling the piston to move down the cylinder under its own weight for the downstroke, wherein the piston has a size and weight such that the suction from the suction device is sufficient to drive the upstroke and the weight of the piston is sufficient to drive the downstroke delivering air to the patient on the downstroke.
5. A ventilator system according to claim 4, wherein the suction device is a vacuum cleaner.
6. A ventilator system according to claim 4 or 5, wherein the suction device is configured to provide a continuous suction to the drive coupling and the valve system is configured to couple the continuous suction from the suction device to the piston to drive the upstroke of the piston and then release the piston from the continuous suction of the suction device such that the piston is free to move down the cylinder under its own weight for the downstroke.
7. A ventilator system according to any preceding claim, wherein the control system is configured to be actuated by the piston at the bottom of the downstroke to engage the drive mechanism and the control system is configured to be actuated by the piston at the top of the upstroke to disengage the drive mechanism.
8. A ventilator system according to any preceding claim, wherein the control system is a mechanically actuated control system.
9. A ventilator system according to any one of claims 1 to 7, wherein the control system comprises an electronic control system.
10. A ventilator system according to any preceding claim, wherein the cylinder comprises two one-way ports located below the piston including a first one-way port which enables air to flow out of the cylinder during the downstroke to the patient and a second one-way port which enables air to flow into the cylinder below the piston during the upstroke.
11. A ventilator system according to any preceding claim, wherein the cylinder comprises a port located above the piston which enables air to flow into the cylinder above the piston during the downstroke thus allowing the piston to move down the cylinder under its own weight during the downstroke without generating a negative pressure above the piston which would otherwise impede the downward motion of the piston.
12. A ventilator system according to claim 11, wherein the control system is configured to close said port during the upstroke and open said port during the downstroke, and wherein the cylinder comprises a further port which is connected, or connectable to, the suction device of claim 4.
13. A ventilator system according to any preceding claim, wherein the size and weight of the piston is selected to generate an outlet air pressure in a range 50 to 1000 mm of water.
14. A ventilator system according to any preceding claim, wherein the size of the cylinder and the stroke length of the piston is selected to deliver a volume of air to the patient on the downstroke in a range 50 ml to 1.5 litres.
15. A ventilator system according to any preceding claim, wherein the size of the cylinder and the stroke length of the piston is selected to deliver a volume of air to the patient on the downstroke in a range 1 to 15 ml per Kg body weight of the patient.
16. A ventilator system according to any preceding claim, wherein the ventilator system is configured to have a cadence in a range 5 to 40 breaths per minute.
17. A ventilator system according to any preceding claims, wherein more than one ventilator is coupled to the drive mechanism.
18. A ventilator system can be provided to aid human or animal respiration comprising: a cylinder; a piston disposed within the cylinder and slidable along the cylinder to provide an outstroke and an instroke respectively; a drive coupling configured to be connected to a drive mechanism to drive the outstroke of the piston by drawing the piston along the cylinder; a biasing means, such as a spring or equivalent, to bias the piston to drive the instroke; and a control system configured to release the piston at the end of the outstroke enabling the piston to move along the cylinder under biasing force from the biasing means for the instroke such that during the instroke of the piston air is forced out of the cylinder through an outlet coupling and into the patient's lungs, the control system being configured to re-engage the drive mechanism at the end of the instroke to drive the outstroke of the piston and draw air into the cylinder from outside the cylinder, wherein the biasing means generates sufficient force to drive the instroke delivering air to the patient on the instroke.
19. Use of a ventilator system according to any preceding claim to aid human respiration.
20. Use of a ventilator system according to any one of claims 1 to 18 to aid animal respiration.
21. A method of aiding human or animal respiration, the method comprising: coupling a ventilator system according to any one of claims 1 to 18 to the airway of a human or animal patient; and operating the ventilator system to deliver air to the patient to aid respiration.