SE500550C2 - Methods and apparatus for reducing gas re-breathing from the harmful space - Google Patents

Abstract

PCT No. PCT/SE91/00435 Sec. 371 Date Dec. 10, 1992 Sec. 102(e) Date Dec. 10, 1992 PCT Filed Jun. 18, 1991 PCT Pub. No. WO91/19526 PCT Pub. Date Dec. 26, 1991.In a method and apparatus for reducing rebreathing of gas from the dead space (i.e., the volume of used gas, which during expiration has filled the airways and is brought back to the alveus at the following inspiration), at least during the final phase of expiration, a flow of used breathing gas is artificially evacuated from the patient through a gas conduit inserted into the patient's airway, the flow rate of evacuated gas being greater than the flow rate of the expiration gas which is being exhaled by the patient at the time. A flow of breathable gas is simultaneously supplied to the patient through gas conduit inserted in the airway, which may be the same conduit as is used for evacuation or a different conduit.

Description

.511 0 10 15 20 25 30 35 550 2 elimination of carbon dioxide, but such measures are extremely resource-intensive and of limited medical applicability.

Positive airway pressures also cause other disadvantages in addition to barotrauma: in circulatory disorders, circulation is often inhibited to a detrimental extent by positive intrapulmonary pressures. In such cases, it is important to try to reduce the positive pressure, and one way to do this is to reduce the volumes by which a patient is ventilated in a respirator.

A well-known principle for the treatment of respiratory insufficiency is to reduce the harmful space, and this can be done by the patient being tracheotomized, which means that a ventilation heel is placed on the neck, which connects the trachea to the outer space, but it is obvious that this action is associated with major disadvantages.

Another previously known principle for the treatment of respiratory insufficiency is that during respiratory treatment via a special gas line a certain amount of respiratory gas is supplied to a point in the airway during the latter part of the exhalation, whereby the volume of gas thus supplied displaces the used respiratory gas. gas from the airway above the mentioned supply point and the harmful space is thereby reduced. This principle, which can be called airway flushing, is useful but has certain limitations and even in some cases certain disadvantages. Thus, the extra gas supply causes a certain increase in the airway pressure, which can be harmful in severe circulatory insufficiency. In mainly obstructive airways disease, there is an abnormally high flow of gas from the alveoli throughout the exhalation. If one then tries to free the airway from used gas by means of airway rinsing, some of the positive effect is lost in that the continued flow of gas from the alveoli eats tends to fill the airway with used gas. gas. It is true that by rinsing with a high flow a strong dilution of the gas flow from the alveoli can be achieved, but then other disadvantages arise, for example further elevated airway pressure.

A further limitation of previously known methods and devices for airway rinsing is that they are connected to a respirator and thus cannot be used by non-respiratory patients.

In order to eliminate or in any case considerably reduce the above-mentioned disadvantages of known methods for reducing gas respiration from the harmful space, the method according to the invention has obtained the features as stated in claim 1.

According to the invention, the device as claimed in claim 8 is proposed for practicing the method.

For a more detailed explanation of the invention, the method according to the invention will be described in connection with the accompanying drawings, in which FIGS. 1 is a diagram showing an embodiment of the device according to the invention for use in connection with respiratory treatment, and FIG. 2 is a diagram. showing an embodiment of the device according to the invention for use in spontaneous breathing.

In FIG. 1. to which reference is first made, two lines are shown for the supply of breathing gases under overpressure, namely a line 10 for the supply of, for example, air and a line 11 for the supply of, for example, oxygen. The lines are connected to a gas mixer 12 for mixing the gases in desired, adjustable proportions. and from the gas mixer a line 13 leads to a respirator 14, which here is assumed to be a respirator of the type Servo fan 900C from Siemens soo sso 4 10 15 20 25 30 35 Elema AB, Solna. The line 13 is also connected via branch lines 15 and 16 to two electrically controlled valve systems 17 and 17, respectively. 18, consisting of a plurality of parallel-connected normally closed micro-valves of the LIF LF AA l200ll8H type from The Lee Company, Westbrook, Connecticut, USA. The respirator 14 has an outlet line 19 for inhalation gas with a humidifier and heater 20, and from this an inhalation hose 21 goes to one leg on a Y-piece 22, the other leg of which is connected to the respirator via an exhalation hose 23. The Y-piece connects the inhalation and exhalation tubes to a tracheal tube 24 which is provided with an inflatable cuff 25 and is intended to be inserted into the patient's trachea, which is indicated at 26. Instead of the tracheal tube, a tracheal cannula may be used. arranged for connection of the respirator to the patient's airway. The valve system 17 is connected to the outlet line 19 via a line 27 via a flow meter 28.

The line 27 is provided with a mechanical non-return valve 29, which constitutes a safety valve for admitting external air into the inhalation hose 21, should there be a negative pressure in this hose, which is about 5 cm of water column. The valve system 18 is connected to a conduit 30, which opens near the mouth of the tracheal tube 24 and which may be a thin catheter, which is placed inside the tracheal tube, or may be designed as an intramural cavity in the tracheal tube in the manner found at Hi Lo. Jet Tracheal Tube from Mallincrodt.

A further conduit 31 is arranged in the same manner as the conduit 30 and also has its mouth near the mouth of the tracheal tube 24, and this conduit is connected via a trap 32 for secretions and a bacteria-tight filter 33. to a unit, connected to a conduit 34, which is connected to a vacuum source, not shown in more detail here, which may be a central evacuation plant or a vacuum pump. Arranged in the line 34 is a flow meter 35 and a flow regulator 36, the latter of which can in principle be of the same type as the valves which control the inhalation and exhalation flows in the respirator of the manufacturer specified here.

The described device includes an electronic control unit 37, which may be of the INTEL type and comprises, among other things, a microprocessor and an analog-to-digital converter. It is connected via a line stem 38 to the respirator 14 in order to obtain signals therefrom which indicate the breathing phase, flows and pressure in the inhalation and exhalation lines 19, 21 and 21, respectively. 23. The flow meters 28 and 35 are also connected to the control unit via lines 39 and 39, respectively. 40 to supply to the control unit signals representing the flows in line 27 and line 34, respectively, while from the control unit a line 41 to the flow regulator 36 and lines 42 and 43 to the valve system 17 resp. 18 for delivering electrical signals to these units from the control unit, when the microvalves are to be opened. The valve systems 17 and 18 are also connected to respective pressure sensors 44 and 44, respectively. 45 via a line 46 resp. 47.

In the respirator 14, pressure sensors 48 and 49 are located in the inhalation line 19, 21 and 21, respectively. the exhalation line 23, which in the respirator is connected to an automatic monitoring system to interrupt the exhalation in the event of an inappropriate negative pressure, for example -2 cm water column. in the exhalation circuit and to interrupt the inhalation, if an inappropriately high overpressure occurs, and also these pressure sensors are connected to the control unit 37 via lines 50 resp. 51.

Using the described device, the method according to the invention is practiced as follows: The respirator 14 operates in the conventional manner, during which gas flows to 5001550 during the inhalation phase! 5001 10 15 20 25 30 35 sso 6 the patient's respiratory system through the conduit 19 via the humidifier and heater 20 and further through the inhalation tube 21, the branch piece 22 and the tracheal tube 24, while during the exhalation phase used gas flows through the tracheal tube and the exhalation tube 23. In accordance with known principles, parts of the harmful space can be flushed out during the latter part of the exhalation by opening one or more valves in the valve system 18 by signal from the control unit 37 via the line 43 and passing a constant or pulsed air flow through the gas line 30 to emit an air jet near the mouth of the tracheal tube 24. Initially, the gas flow through the exhalation hose 23 is used gas, but in the man used gas does not continue to flow up from the lungs, parts of the patient's airway and tracheal tube 24 and Y-piece 22 are filled with fresh from the gas line 30, whereby the efficiency of gas leaching is reduced.

This inconvenience is eliminated by comparing the current exhalation flow in the control unit with a flow programmed in this unit, so that when the falling exhalation flow falls below a predetermined value, it must leave the control unit via the line. 41, a signal is provided to the flow regulator 36, thereby causing it to open to such an extent that a pre-selected and programmed flow is controlled from the patient's respiratory system via line 31, separator 33 and flow meter 35 through the suction source connected to line 34. This flow should preferably be selected to be of the same order of magnitude as the exhalation flow which triggers the function just described. Thereby, the flow from the patient's respiratory system during the latter part of the exhalation phase will be evacuated via the line 31 and the corresponding flow through the tracheal tube 24 will cease.

At the same time as the described evacuation is started, a signal is sent from the control unit via the line 42 to the valve system 17 so that during the exhalation phase this valve system is allowed to release a preset flow through the line 27 via the flow meter 28 to the ventilator 14 outlet line 19 and via the humidifier and heater 20 to the inhalation hose 21. As the flow of exhaled gas through the trachea 26 during the advancing exhalation phase further falls during the last part of the exhalation phase, this latter flow will fall below the flow sucked out via the line 31, which causes sequence. that there is a flow from the inhalation tube 21 via the Y-piece 22 and the tracheal tube 24. Fresh heated and humidified gas will thus be supplied to the breathing circuit down to the lower end of the tracheal tube 24 during the latter part of the exhalation phase. If the flow of gas supplied to the respiratory circuit in this way is not judged sufficient to flush the entire respiratory circuit down to the lower end of the tracheal tube, the flow evacuated through line 31 and the flow supplied through line 27 via valve system 17 may be increased. to an appropriate extent. It has been found appropriate to control these two flows in such a way that the flow through the line 27 is slightly higher than the flow through the line 31. since this has the advantage that the flow through the exhalation hose 23 is affected in small men. The size of the latter flow is, among other things, important for the monitoring systems which are included in the device for checking that the patient receives adequate ventilation and whose function is to be described in more detail below. At the same time, however, a certain flow is also obtained. which rinses both legs of the Y-piece 22 and prevents re-breathing via gas turbulence, 5Û0w 10 15 20 25 30 35 559 8 which is located in the exhalation leg of the Y-piece. Furthermore, the advantage is gained that a final respiratory pressure set on the respirator 14 is better maintained in the presence of minor leakage, which may occur mainly in the connection between the tracheal tube 24 and the trachea 26 at the cuff 25.

When applying the method according to the invention using it in connection with FIG. In the device described in Fig. 1, fresh gas will be brought during the exhalation phase to fill the airway down to the tip of the tracheal tube 24 by control by means of the valve system 17 for rinsing out the harmful space. Further flushing is effected by the gas jet supplied through the conduit 30 by control by means of the valve system 18, and the gas jet thus supplied at the mouth of the conduit 30 at the lower end of the tracheal tube will reach down into the trachea and the nearest generations of airways, which can thus be flushed out. In this case, the gas flow which is extracted via the line 31 should preferably be regulated by means of the regulator 36 in such a way that its size corresponds mainly to the sum of the flows supplied via the valve system 17 and 18. The control is controlled by means of the control unit 37.

In order not to create inappropriately high airway pressures in the airway when the device according to FIG. 1 or in the event of a malfunction of this device, the device has several safety systems. Mention has previously been made of the two pressure sensors in the respirator 14, which are connected to the control unit 37 and which, in the event of an inappropriately high overpressure as a result of more gas being sucked out through the line 31 than supplied by the patient's exhalation and through valve systems 17 and 18, the exhalation is interrupted, whereby the valve systems 17 and 18 and the flow regulator 36 10 15 20 25 30 35 9 i + 5so sso are caused to close by signals from the control unit 37, which are initiated by signals from the pressure sensors 48 and 49 via the lines 50 and 51. If this should occur a negative pressure due to improperly set respirator 14 or malfunction thereof, there is a safety function built into the control unit 37, in that the valve systems 17 and 18 and the flow regulator 36 are closed due to signals from the pressure sensors 48 and 49 via the lines 50 and 51 to the control unit 37, if the pressure sensors indicate a value corresponding to -4 cm water column. The previously mentioned mechanical valve 29 comes into operation and opens at a negative pressure of -5 cm water column, should both pressure sensors 48 and 49 be faulty or a fault should occur in the control unit 37.

The pressure sensors 44 and 45, which are connected via the lines 46 and 47 to the valve system 17 and 17, respectively. valve system 18, causes these valve systems to close if the pressure in the tracheal tube 24 should exceed a preset value for each valve system.

This safety function must be such that manual reset is required for the valve systems to eat open.

The embodiment of the device according to the invention, shown in FIG. 2, is intended for use by patients during spontaneous breathing. In this case, a subcutaneous type catheter 52 is connected to the trachea 26. but instead a catheter could be inserted via the natural airway and have its mouth in any place in the airway, for example in the nasopharynx. Connected to the catheter is a two-way valve 53, by means of which a pressure sensor 54 of the type used in measuring pressure inside body cavities can be connected to measure either the atmospheric pressure or the pressure in the catheter. The catheter is connected via an artificial nose 55 and a branch piece 56 to two lines 57 and 58, of which line 57 leads to an evacuation system 59 and line 58 leads to a system 60 for gas supply. The artificial nose is made according to previously known principles and contains a porous hygroscopic material, which takes advantage of heat and moisture, when hot and moist exhaled gas passes through the artificial nose to the evacuation system 59, to then return during inhalation. heat and moisture to the inhaled gas.

Each system 59 resp. 60 comprises a pressure sensor 61 resp. 62 of the type included in the above-mentioned respirator of type Servoventilator 9OOC, and a flow meter 63 resp. 64, also of the same type as in Servo fan 900C. Furthermore, each system includes 59 resp. 60 a plurality of parallel-connected micro-valves of the type LIF LF AA 1200118H from The Lee Company, which are marked with a valve symbol 65 resp. 66. The evacuation system 59 is connected via the valves 65 to a line 67. not shown source of negative pressure, which may be for instance a central system for gas evacuation or an evacuation pump for gases, while the system which goes to one in FIG. 2 for gas supply via the valves 66 is connected to a line 68, which comes from one in FIG. 2 not shown source of respiratory gas under overpressure.

The pressure sensors 61 and 62 are via lines 69 and 69, respectively. 70 connected to an electronic control unit 71, which comprises, inter alia, an analog / digital converter and a microprocessor. The control unit is also via lines 72 resp. 73 connected to the two flow sensors 63 and 64. Via the lines 69, 70, 72 and 73 the control unit receives signals which indicate pressure resp. flow in lines 57 and 58. The control unit is also connected to lines 65 and 75 via lines 74 and 75, respectively. 66 10 15 20 25 30 35 1, 2: 5 @@ = sso to give signals via these lines, whereby a suitable number of the normally closed valves are caused to assume an open position. A line 76 is provided from the pressure sensor 54 to the control unit 71 for delivering a pressure signal to the control unit, which has a line 77 to the two-way valve 53 for switching it between its two setting positions, the atmosphere resp. the catheter.

To line 58 is also upstream of the flow meter 64 via a valve system, in FIG. 2 marked with a valve symbol 78, of the same type as the valve systems 65 and 66 connected to a line 79, which via a pressure regulator 80 is connected to a source of oxygen or other gas. The normally closed valves 78 are connected through a line 81 to the control unit 71 in order for a suitable number of valves to be opened on a signal from the control unit.

The device according to FIG. 2 operates according to routines, which must be programmed in the control unit 71 according to the examples given below.

In a first phase, which according to the program is repeated at a suitable interval, the pressure sensor 54 is connected to the atmosphere by a pulse transmitted via the line 77 from the control unit 71 diverts the two-way valve 53. During the following period the control unit 71 reads the signal from the pressure sensor 54. which corresponds to atmospheric pressure. Thereafter, the two-way valve 53 is reset so that the pressure sensor 54 is connected to the airway via the catheter S2.

In a second phase, the microprocessor, which enters the control unit 71, reads the signals from all three pressure sensors 54, 61 and 62, for a period of time corresponding to a number of breaths. The pressure signals are then compared with each other by linear regression. In the case where the three signals do not show congruence, an error message is issued and further functions are inhibited until the error has been rectified and a manual restart of the system has taken place.

In normal cases, the numerical constants are stored in the microprocessor, which allow direct comparison between the measured pressure signals.

In a third phase, the pressure profile read during the second phase is analyzed to identify the beginning and end of the inhalations and exhalations. Lowest measured pressure, which is subatmospheric. on this inhalation is sought and identi- as registered. controlled be identified as an inhalation. The beginning is celebrated as the zero passage of the pressure, which precedes the previously found minimum pressure. Should there be a zero pass during the loaded period, the onset of inhalation is left unidentified. Additional pressure minima and the preceding zero passages are searched for to identify additional inhalations and their onset throughout the entire period read during the second phase. Appropriate filters and "eye-closing" periods are used to eliminate double identification of an inhalation. In the next step of phase three, pressure maxima are sought between successive inhalations. It is checked that pressure maxima are above atmospheric pressure, after which maxima are identified as exhalation.

The beginning of each exhalation is identified as the zero crossing of the pressure signal that precedes the respective pressure maximum. The duration of inhalation and exhalation are tabulated in the microprocessor together with the respective pressure minima and pressure maxima. The course of a typical inhalation and exhalation is determined as the end result of the process during phase three, and the typical pressure course in curve form together with numerical information, including in particular the duration of different phases of the breathing cycle, is presented on a screen.

During a fourth phase, the course of a therapist, who is presumed to be a doctor or respiratory therapist, is studied in the registered 10 15 20 25 30 35 _5ÛÛ. This determines the volumes that are to be evacuated during the breathing cycle via line 57, and during which phase of the breathing cycle this is to take place. Furthermore, the therapist determines the volumes to be delivered via line 58 and during which phase of the breathing cycle this is to take place.

The therapist also sets maximum values for negative pressure in catheter 52 during the evacuation phase, as well as maximum values for overpressure in the catheter during gas supply. Limits with regard to deviations from the typical breathing pattern studied during phase three are also established.

During a fifth phase, which is a therapeutic phase, the device is made to function in accordance with the principles of the invention and in accordance with the routine established during phase four. Throughout the therapeutic phase, the control system continuously reads pressure values from the three pressure sensors 54, 61 and 62, as well as flow values from the flow meters 63 and 64. The digital values are stored in a circle buffer in the microprocessor memory, which circle buffer comprises a period of time covering several breathing cycles. A subatmospheric pressure minimum is sought and identified as an inhalation. Then a supermospheric pressure maximum is sought, which defines an exhalation. When this has been found, the computer searches for the beginning of the current exhalation, which is identified as the immediately preceding zero crossing of the pressure and is found in the circle buffer. The processor checks that the time relationships between the previous inhalation pressure minimum, the beginning of the current exhalation and its identified pressure maximum correspond to what has been determined in phase four to constitute a normal breathing pattern for the patient. If this is the case, after a period of time defined during phase four, the processor sends a signal to the 50050 valve system 65, which transmits an evacuation flow, which is aspirated via the catheter 52, the artificial nose 55. the line 57 , the flow meter 63, the valve system 65 and out through the line 67. The size of the evacuation flow is compared according to known servo feedback principles with the flow which corresponds to that required for the evacuation volume determined during the fourth phase to be extracted for the determined period. Occurring deviations are corrected by connecting or disconnecting parallel-connected valves in the valve system 65. As described, during the latter part of the exhalation a flow will be sucked out of the airway from the point where the catheter 52 opens. As the flow of gas from the lungs during exhalation decreases and approaches zero, it will at some point fall short of the flow with which gas is aspirated via the catheter 52. Thereafter, gas will flow from the airway orifice, which depending on the patient's breathing may be nasal. or mouth, down the airway toward the mouth of the catheter 52 therein. The airway will thus be filled from above with fresh breathing gas during the latter part of the exhalation as a result of gas from the harmful presence of evacuated used gas being extracted from the airway. It should be noted, beneficial effect until during the inhalation the separation zone between used gas and fresh gas has passed the mouth of the catheter 52, the latter in which all used gas above this mouth has not already been sucked out during the exhalation.

The function during the fifth therapeutic phase can be varied according to the therapeutic program established during phase four. After a certain volume of gas has been evacuated during a portion of the final phase of the expiration, according to a program, the valves in system 65 close. The control system then checks that a superatmospheric or atmospheric pressure prevails in the airway. as a sign that inhalation has not yet begun. by reading the signal from the very fast pressure sensor 54. During the last part of the exhalation pulses of gas are given according to a regime determined during phase four by the control system 71 transmitting signals through the line 75, which lead to the opening of valves in the system 66 during further control of a servo-reconnected system, so that the flow measured by the flow meter 64 corresponds to that determined.

Alternating with the flow pulses thus obtained, an evacuation of corresponding volumes of gas takes place by the control system causing valves in the system 65 to open. Through this procedure, additional volumes of spent gas can be flushed out of the airway during the final stage of exhalation.

It is common in patients with respiratory failure to use a catheter 52 of the type shown in FIG. 2, and using catheters which are inserted through the natural airway. The purpose of these catheters is to supply the patient with respiratory gases other than air, usually oxygen. The device according to FIG. 2 offers significant advantages in this respect compared with previously known systems for gas supply.

It absorbs heat and moisture from the extracted gas and reproduces this heat and moisture to the gas, which is then supplied to the patient. This eliminates the need for complicated devices for heating and humidifying the supplied gases. The construction offers a very economically great advantage in that it allows gas supply to be controlled so that it takes place only during an early part of the inhalation, whereby the supplied gas, typically oxygen, will be supplied in its entirety to the alveolar space to promotion of blood oxygenation. This advantage can be utilized without influencing the functions described above by additional supply of oxygen through line 58. After evacuation and rinsing of the airway during the fifth therapeutic phase above, the pressure in the airway is read by pressure. the sensor 54. When the pressure has dropped to the subatmospheric level, which means that an inhalation has started, the control unit 71 sends signals via the line 81, which causes valves in the valve system 78 to open during further servo-controlled control, so that the intended flow of gas is administered to the patient for the intended time, which is suitably limited to the earlier part of the inhalation, so that the entire volume of gas supplied safely reaches the alveolar space during the inhalation. Thereafter, the control system returns to the task of identifying the following exhalation as described above.

The device according to FIG. 2 has a number of built-in safety systems. Checking that the piping system works involves measuring the pressures at the three points where the pressure sensors 54, 61 and 62 are located.

The pressure differences are set in relation to the simultaneously measured flows, which allows the resistance in the catheter 52, the artificial nose 55 and in the lines 57 and 58 to be calculated. in the control unit 71 with previously established guide values.

These resistances are compared when deviating from the limit values based on them, the function of the device is interrupted and an alarm is issued. An additional safety test is performed in connection with the current in line 57 and 58 being interrupted momentarily. The interruption shall correspond to a corresponding step response in the pressure measured with the rapid pressure sensor 54. If this response is not the expected one, the catheter may have been dislocated and the function of the device interrupted. An important safety function is to interrupt the evacuation of gas if the patient has closed the airway above the point from which gas is extracted. This gives rise to an abnormally low pressure, registered by the pressure sensor 62.

Claims (13)

10 15 20 25 30 35 '_5Û "í @' f155-Û 1? PATENTKRAV A method of reducing the re-breathing of gas from the harmful space, characterized in that during at least the final phase of the exhalation a flow of used breathing gas is sucked out through a gas line introduced into the airway, this flow being greater than the flow of breathing gas leaving the respiratory system during the final phase of the exhalation / and that a flow of gas is supplied to the airway mainly at the same time through a separate gas line introduced into the airway. 2. A method according to claim 1, characterized in that the extraction of breathing gas is initiated at a predetermined flow of exhaling gas. 3. A method according to claim 2, characterized in that the extraction of breathing gas and the supply of gas takes place alternately with each other through one and the same gas line. 4. A method according to claim 3, characterized in that extracted and supplied gas volumes are controlled to be in a predetermined mutual relationship. 5. A method according to any one of claims 2 - 4, characterized in that the flow of supplied gas is heated and humidified. 6. A method according to claim 5, characterized in that the flow of supplied gas is supplied with heat and moisture, which is delivered by exhaled gas. 7. A method according to claim 6, characterized in that heat and moisture are taken from the extracted flow of used breathing gas. Device for reducing the re-breathing of gas from the harmful space, combined with a respirator, characterized by a conduit arranged for insertion into the respiratory tract, which is connected to or arranged 10 15 20 25 500 550/3 as a separate channel in a tracheal tube connected to the respirator for supplying and diverting respiratory gas, means connected to the line for producing negative pressure in the line, means for determining an end phase in the exhalation of the patient to be treated, means for initiating negative pressure in the line in dependent of such determination and means for supplying gas to the tracheal tube during the exhalation phase of the respirator. Device according to claim 8, characterized in that said means for determining a final phase in the exhalation consists of means for measuring the exhaled flow in the respirator and comparing this flow with a predetermined value. 10. Device according to claim 9, characterized in that said means for determining a final phase in the exhalation comprises a pressure sensor arranged on the line. 11. ll. Device according to claim 10, characterized in that the line is arranged with a branch for connection to an evacuation device and a device for supplying gas via shut-off valves, respectively. Device according to claim ll, characterized in that the conduit is provided with an artificial nose. Device according to claim 12, characterized in that means are provided for alternating actuation of the valves to the open position.