GB2136298A

GB2136298A - Respiratory apparatus

Info

Publication number: GB2136298A
Application number: GB08404441A
Authority: GB
Inventors: Uwe Kuhl; Eckhardt Muller
Original assignee: Draegerwerk AG and Co KGaA
Current assignee: Draegerwerk AG and Co KGaA
Priority date: 1983-03-12
Filing date: 1984-02-20
Publication date: 1984-09-19
Also published as: JPS59168859A; GB8404441D0; DE3308819A1; SE454951B; JPS6319188B2; GB2136298B; FR2542204A1; SE8306413L; FR2542204B1; SE8306413D0; CH661210A5

Abstract

A respiratory apparatus comprises, in the direction of flow of gas, a high frequency valve (3), a respiratory gas heater (4) and a jet outlet (5). Between the heater (14) and the outlet (5), steam from a steam generating device (10, 14) is injected via steam line (9) into a respiratory gas line (2) this injection being carried out as a function of the respiratory gas pulses. The steam has a high temperature and water content, making it possible to ensure-a high relative moisture in the expanded respiratory gas mixture at the desired temperature of 37 DEG C. Only a low heat capacity is required for further heating of the respiratory gas. The low volume in the respiratory gas and the steam line guarantee the sharpness of the high frequency pulses in the respiratory gas mixture. <IMAGE>

Description

SPECIFICATION Respiratory apparatus This invention relates to a respiratory apparatus.

A major problem in connection with respiratory apparatus for effecting high frequency jet ventilation (HFJV) arises over the control of the mositening and temperature of respiratory gas.

The gas mixture supplied to a patient comprises two portions: the respiratory gas introduced under high admission pressure through a jet or hollow needle (jet-ventilation); and an additional gas drawn in by injection action. Gas pressure pulses are thus produced in the respiratory gas flow during the high frequency ventilation.

A known device for supporting respiration or artificial ventilation of humans is disclosed in German Offenlegungsschrift No. 26 03 063. This device comprises a thin jet pipe which is arranged parallel to the axis of an endotracheal tube. The respiratory gas is supplied under pressure to this jet pipe via a control device. The gas jet directed into the endotracheal tube inflates the lungs. In the region of the opening of the jet pipe and at one side thereof, a supply pipe for moisture is provided in the wall of the endotracheal tube. Moisture is drawn off from the supply pipe by the injector action of the respiratory gas jet. The moisture may be supplied as atomised water, moist air or steam.

However, the use of atomised water results in undesirable cooling of the patient's body as a result of the latent heat of evaporation of the water. The moisture content of moist air is reduced by the respiratory gas jet so that the required high degree of moisture cannot be attained. The introduction of steam directly into the endotracheal tube involves high risks because of the temperature of the steam.

In a known ventilator with high frequency ventilation, (described in Respiratory Care, November 1982, Vol. 27, No. 11, pages 1386-1391) a respiratory gas source in the form of an oxygen-air mixer is connected to a respiratory gas line via a first heat exchanger, a solenoid valve and a second heat exchanger having a jet outlet. The jet outlet is arranged in an endotracheal tube. A metering pump is connected via a non-return valve to the respiratory gas line between the solenoid valve and the second heat exchanger. The pump delivers a prescribed flow of liquid water into the respiratory gas line. The solenoid valve is driven at high frequency by a control system, conducting respiratory gas pulses under pressures of up to 3.5 bars from the respiratory gas source to the jet outlet.During its passage this respiratory gas is pre-heated in the first heat exchanger, is provided with the required amount of water downstream of the solenoid valve and is subsequently heated in the second heat exchanger until the added water vaporises.

When it leaves the jet outlet the respiratory gas should be at body temperature and be saturated with moisture. However, this cannot be achieved by vaporisation in the second heat exchanger of the water which has been added to the pressurised respiratory gas because, as a result of the conditions of equilibrium during pre-heating to normal temperatures, the respiratory gas does not contain sufficient moisture when the pressure is removed; or, with greater preliminary heating, the moisture is increased in the required manner, but at the same time the temperature rises unjustifiably. Moreover, as a result of the spaces in the second heat exchanger, a buffer volume is produced which equalises the high frequency respiratory gas pulses produced by the solenoid valve and thus undesirably alters their effect.

In accordance with the present invention there is provided a respiratory apparatus comprising: a steam generating device having an inlet for water and an outlet for steam; a control device; a respiratory gas line; and, arranged in the respiratory gas line, a high frequency valve, for supplying pulsed respiratory gas to the patient from a respiratory gas source, and a heater, the respiratory gas line being in communication with the outlet for steam downstream of the heater wherein the control device is such as to control the steam generating device in dependence on the operation of the high-frequency valve.

The form of the steam generating device is optional. For example, it may comprise: a hollow coil to which water is supplied, the coil being heated to produce the steam; and a metering pump which supplies water to the coil in response to the control device.

Alternatively, it may comprise a pressure vessel to which water is supplied, and an open-shut valve disposed between the outlet for steam and the respiratory gas line, the valve being operated in response to the control device.

In an embodiment of the invention a steam generating device, to which water is supplied, is connected, via a steam line and between the heater and a jet outlet of the respiratory gas line, to the respiratory gas line; and the control device switches the steam generating device as a function of the high frequency valve.

The advantages of an apparatus in accordance with the present invention lie in the fact that gas is available for the patient in an unpressurised state at a temperature of 370C and with a high relative moisture content, without the pulse sharpness of the respiratory gas pulses being essentially impaired.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which .~ Figure 1 shows the high pressure end of a respiratory apparatus in accordance with one embodiment of the present invention, the steam being produced in a steam coil; and Figure 2 shows the high pressure end of a respiratory apparatus according to another embodiment of the present invention, the steam being produced in a pressure vessel.

The apparatus comprises a high frequency/high pressure end for respiratory gas (shown in the drawing) and provision (not shown) for an additional gas component connected to the jet outlet 5 to the patient.

The respiratory gas under high pressure is introduced from a respiratory gas source at 1 into a respiratory gas line 2, and then passes through a high frequency valve 3, a respiratory gas heater 4 and the jet outlet 5. Here the pressure is released and the gas is blown at 6 in the direction of the patient.

The high frequency valve 3 is controlled by control means 7.

Between the respiratory gas heater 4 and the jet outlet 5, a steam line 9 is connected at 8 to the respiratory gas line 2 and the steam produced in a steam generating device (10, 14) is injected through this steam line 9, controlled by the control means 7 dependent on the action of the high frequency valve 3.

Figure 1 shows a steam generating device comprising a narrow steam coil 10, which may be a metal pipe with an internal diameter of between 0.3 mm and 1.5 m, heated in a conventional manner from the outside, and a metering pump 12. The water to be evaporated is supplied at 1 1 and forced by the metering pump 12, controlled by the control means 7, through a water line 13 into the steam coil 10. Here it is evaporated and injected, as steam, through the steam line 9 into the respiratory gas line 2. It mixes here with the respiratory gas heated in the respiratory gas heater 4.

Figure 2 shows a steam generating device which comprises a pressure vessel 14, to which water is supplied at 11 , and a connected openclosed valve 15. Steam is produced constantly in the pressure vessel 14 and is then injected into the respiratory gas line 2 through the steam line 9 via the open-close valve 15 which is controlled by the control means 7 in dependence on the action of the high frequency valve 3.

The temperature of the steam produced in the steam generating devices and which is injected by the pressure of the respiratory gas in the respiratory gas line 2 into this line, is adapted according to the pressure prevailing in the respiratory gas line 2, for example the temperature may be 1 600C. The steam then contains a volume of water which, after the release of the pressure of the steam mixture downstream of the jet outlet 5, and a at a temperature of 370C, represents the desired high relative moisture content. The temperature of the mixture of the supplied respiratory gas and the steam is only slightly below the subsequently required temperature of 370C. Only a slight heating capacity is therefore necessary in the respiratory gas heater 4 in order to reach this temperature.The short period the gas mixture spends in the respiratory gas line 2 means that there is no interfering recondensation of the water.

The steam is injected into the respiratory gas line at least at the pressure prevailing there, and at a correspondingly high temperature. Thus, when the pressure decreases a high relative moisture content at the desired temperature for the patient of 37 OC is achieved. As most of the energy required for moistening and heating the respiratory gas is yielded with this process by the steam, only a small additional heating capacity is required to heat the respiratory gas mixture to the required 370C. This allows the geometric layout of the respiratory gas heater to be such that the heater has a small internal volume and low flow resistance so that the respiratory gas pulses are only slightly attenuated. As the individual respiratory gas pulses spend only a short time in the respiratory gas line, any re-condensation~is prevented. In the event of a partial condensation, the respiratory gas is heated up to such a degree that after the pressure is removed, there is enough heat energy to re-evaporate the small concentration of droplets.

Claims

1. A respiratory apparatus comprising: a steam generating device having an inlet for water and an outlet for steam; a control device; a respiratory gas line: and, arranged in the respiratory gas line, a high frequency valve, for supplying pulsed respiratory gas to the patient from a respiratory gas source, and a heater, the respiratory gas line being in communication with the outlet for steam downstream of the heater wherein the control device is such as to control the steam generating device in dependence on the operation of the high-frequency valve.

2. A respiratory apparatus as claimed in claim 1 , wherein the respiratory gas line has a jet outlet through which the pulsed respiratory gas is supplied to the patient.

3. A respiratory apparatus as claimed in claim 1, wherein the steam generating device comprises a hollow coil to which water is supplied under the control of the control device, the coil being heated to produce the steam.

4. A respiratory apparatus as claimed in claim 3, further comprising a metering pump which supplies water to the hollow coil in response to the control device.

5. A respiratory apparatus as claimed in claim 3 or 4, wherein the coil comprises a metal pipe having an internal diameter of between 0.3 mm to

1.5 mm.

6. A respiratory apparatus as claimed in claim 1, wherein the steam generating device comprises a pressure vessel to which water is supplied, and an open-shut valve disposed between the outlet for steam and the respiratory gas line, the valve being operated in response to the control device.

7. A respiratory apparatus substantially as hereinbefore described with reference to, and as shown in, Figure 1 or 2 of the accompanying drawing.