This invention relates to respiratory therapy apparatus including a patient breathing interface having a gas inlet and a gas outlet connected with a pressure relief valve that is opened to atmosphere when pressure within the interface rises above a set therapeutic level, the gas inlet being connected to an outlet of a gas entrainment device having an atmospheric inlet and an enlraining inlet arranged to be connected to a supply of elevated gas pressure such that gas supplied to the entraining inlet entrains air from the atmospheric inlet to the outlet of the entrainment device and to the gas inlet of the breathing interface.

Patients suffering from respiratory ailments such as asthma or COPD may be treated with a respiratory therapy device incorporating a continuous positive air pressure (CPAP) or a bi-level positive pressure therapy function. This can be achieved using a demand valve that provides a pressure above atmosphere to the patient only when he breathes in. Alternatively, an air entrainment device run from a pressurised source of oxygen, such as a low-flow oxygen therapy line, may be used to provide a gas jet that entrains air from the atmosphere to deliver a continuous mix of air and oxygen above atmospheric pressure to the patient. Both arrangements extend the alveoli in the lungs thereby improving gaseous exchange and blood saturation without the need for the patient to extend his thoracic muscles as much on each breath.

Devices that deliver oxygen via a demand valve do this only during the inspiratory phase and thereby conserve the use of oxygen. However, devices that deliver a gas mix continuously use oxygen continuously but this typically only makes up about one third of the gas mix whilst giving a total concentration of oxygen in the mix of about 50%. This helps conserve the oxygen, which is particularly important where this is obtained from an oxygen cylinder.

Although the increased concentration of oxygen may be beneficial to the patient, the primary mechanism that achieves the therapy is the elevated pressure produced by the CPAP or bi-level positive pressure devices. One problem with conventional air entrainment apparatus is that the only way of increasing the patient back pressure is by increasing the jet flow, which leads to an increased consumption of oxygen from the compressed gas cylinder. This can be a particular problem where the therapy device is used in locations where replacement oxygen cylinders may not be readily available. This may mean delays in providing patients with the therapy they need.

It is an object of the present invention to provide alternative respiratory therapy apparatus.

According to one aspect of the present invention there is provided respiratory therapy apparatus of the above-specified kind, characterised in that the supply of gas at elevated pressure to the entraining inlet of the entrainment device is controlled by breathing of the patient such that gas flow to the entrainment device is enabled during inspiration and is hindered during exhalation.

The respiratory therapy apparatus preferably includes a control valve connected in line between the entraining inlet of the entrainment device and the supply of elevated gas pressure, the control valve being connected with the pressure relief valve such that the control valve is controlled to hinder flow of gas from the supply of elevated pressure when the pressure relief valve is open during exhalation. The control valve may be connected with the pressure relief valve by a drive rod, the drive rod being displaced by the pressure relief valve when the pressure relief valve is opened thereby to close the control valve. The breathing interface preferably includes a face mask. The apparatus may include a bag reservoir connected between the gas inlet of the breathing interface and the outlet of the entrainment device.

According to another aspect of the present invention there is provided a respiratory therapy system including apparatus according to the above one aspect of the present invention and a supply of gas at elevated pressure. The supply of gas at elevated pressure preferably includes a source of oxygen at higher than atmospheric concentrations. The supply of gas at elevated pressure preferably includes a cylinder of compressed gas.

A respiratory therapy system including respiratory therapy apparatus and a source of elevated gas pressure, both according to the present invention, will now be described, by way of example, with reference to the accompanying drawing which shows the system schematically.

The respiratory therapy system includes respiratory therapy apparatus 100 and a source 200 of gas at elevated pressure. The apparatus 100 is arranged to deliver a continuous mixture of air and oxygen at an elevated pressure (CPAP) to a patient. The apparatus includes a patient breathing interface device in the form of a face mask 1, although alternative interfaces would be possible, such as a modified mouthpiece. The mask 1 has a separate inlet 10 and outlet 11, although it could instead have a single opening connected away from the mask to an inlet and outlet. The inlet 10 is connected in line with the patient end 13 of a conventional gas entrainment device 14. The machine end of the entrainment device 14 is open to atmosphere to provide an atmospheric inlet 15, which may be flared outwardly and supports coaxially within it an entraining inlet in the form of a gas nozzle 16 directed downstream towards the patient end 13 of the device. The gas nozzle 16 opens into an entrainment chamber 17 of conventional form where gas from the nozzle interacts with air from atmosphere drawn in to the device from its open, machine end 15. The nozzle 16 is connected via a tube 18 to an entraining inlet in the form of a spigot 19 on the outside of the housing of the entrainment device 14.

The apparatus 100 further includes a control or shut-off valve 23 that is connected in series between the source 200 of gas at elevated pressure and the spigot 19 on the entrainment device 14 by means of tubing 20. The tubing 20 extends to the low-flow output of a regulator 21 on a cylinder 22 of compressed oxygen.

The apparatus 100 also includes an optional bag reservoir 25 in communication with one branch of a T-piece 26 connected between the inlet 10 of breathing interface 1 and the patient end 13 of the entrainment device 14. The bag reservoir 25 contains a varying volume of the air and oxygen mixture to accommodate variations in patient demand levels.

The outlet 11 of the mask 1 is connected to the inlet 30 a pressure relief valve 31. The relief valve 31 has a natural closed state (so that gas cannot flow out from the outlet 11) until pressure at its inlet rises above a desired therapy level when it opens to allow gas to flow through the valve from its inlet 30 to atmosphere via its outlet 32. The pressure relief valve 31 is preferably adjustable so that the opening pressure can be set by the clinician at a suitable value that the patient can achieve for the desired therapy period and that will produce a therapy effect on the patient.

The pressure relief valve 31 is mechanically connected with the control or shut-off valve 23 such as by means of a pilot or drive rod 33, or some other link, which may be mechanical or electrical, so that the rod is displaced when the shut-off valve changes state. More particularly, the shut-off valve 23 and pressure relief valve 31 are arranged such that the shut-off valve is closed to mainly prevent flow (entirely or mainly) of gas through the valve when the relief valve is opened by patient exhalation.

It can be seen that the apparatus of the present invention enables elevated level pressure therapies to be delivered to the patient with very little waste of the driving gas since flow of this gas is blocked during patient exhalation.

Instead of driving the control or shut-off valve directly from the patient relief valve as described above it could be piloted via a pressure line connected with the breathing interface so that a negative (inspiratory) pressure within the interface causes the shut-off valve to open and driving gas to be supplied to the entrainment device. When pressure in the patient breathing interface rises, towards the end of the inspiratory phase or during the expiratory phase, the shut-off valve is closed via the pilot pressure line to prevent driving gas from being supplied to the entrainment device. Alternatively, the apparatus could include an electrical pressure transducer connected in the patient outlet to be responsive to pressure exerted by the patient. The output of the transducer would then be used to control operation of a solenoid valve connected between the source of compressed oxygen and the inlet of the air entrainment device such that oxygen is only supplied to the air entrainment device during the inspiratory phase, as indicated by an output from the pressure transducer, which is in turn indicative of a fall in pressure below a threshold level.

Although oxygen would be the usual driving gas used as the source at elevated pressure, it would be possible to use other gases or gas mixtures since the main therapeutic effect derived from use of the apparatus arises from the elevated pressure rather than from the oxygen enrichment. The pressurised gas could be a gas mixture containing oxygen at higher than atmospheric concentrations.