EP2214763A1

EP2214763A1 - Respiratory gas humidifier for use in mr tomography

Info

Publication number: EP2214763A1
Application number: EP08848820A
Authority: EP
Inventors: Torsten Hertz
Original assignee: LMT Lammers Medical Tech GmbH
Current assignee: LMT Lammers Medical Tech GmbH
Priority date: 2007-11-13
Filing date: 2008-11-13
Publication date: 2010-08-11
Also published as: DE202007015930U1; US20110227237A1; WO2009062715A1

Abstract

The invention relates to a respiratory gas humidifier for heating and humidifying respiratory air, having a humidifier module (9) through which water and respiratory air flow, the water and respiratory air flows being separated by flat elements that are permeable to water vapor, said respiratory gas humidifier having a fluid pump (2) and a heating element (4) for the water, characterized in that the fluid pump (2) is a piezo pump.

Description

Breathing gas humidifier for use on MR tomographs

The invention relates to a respiratory gas humidifier for heating and humidifying the respiratory air for use in combination with transport and / or intensive care ventilators according to the preamble of claim 1. In particular, the invention also relates to a respiratory gas humidifier, which is suitable for use in MR tomographs.

Adult or neonatal ventilators are supplied with compressed gas (oxygen and compressed air) from bottles or via the wall connections in the hospital room. This compressed gas is dry and after the relaxation of line pressure

Ventilation pressure also cold. Since dry, cold air from the ventilator would damage the patient's lungs and cause additional heat loss, the intensive care unit uses humidifiers that allow air heating and humidification to physiological conditions.

A hitherto very common concept for moistening and warming the breathing gases is the Kocherprinzip, in which the respiratory gas flow is passed over heated water. An electric heater ensures water heating. through

Temperature sensors is performed in a closed loop system monitoring. In another concept, water is passed through hollow fiber elements with an electric fluid pump (DC drive) which are heated via AC heating elements. These fibers are flowed around outside of warm water and inside of the breathing air. The pump operates to maintain the volume flow at a constant speed.

In any case, the conversion of electrical into kinetic energy is based on temporally and / or spatially variable magnetic fields. It is not surprising that this drive concept reaches its limits in the environment of strong external magnetic fields when the field of application of the motor is superimposed on the external interference field and the required continuous rotational movement is disturbed or prevented. This is precisely the case when introducing a humidifier in the homogeneous field of an MRI magnet (magnet of a Magnet_resonanzt_omographen or magnetic resonance imaging) the case. Furthermore, the control electronics are not suitable for use in the vicinity of the radiofrequency fields of a magnetic resonance tomograph.

Known technical approaches for use in magnetic resonance tomographs are limited to e.g. The use of magnetic shielding of the motor and the electronics as well as spatial displacement of the motor to a point of lower interference field strength, so as far as possible away from the homogeneous

Field and stray field of the magnet to try to avoid these problems. However, none of the measures provide satisfactory results for the humidification of respiratory gases for newborns and adults with regard to:

1. MRI magnetic field strengths from 1.5 Tesla

2. Impairment of MRI imaging 3. Achievement of physiological respiratory humidity and breathing gas temperature

4. Transport incubator and humidifier, if they are designed to avoid the above disorders as separate and objected to each other equipment.

The object of the invention is to provide a controlled humidification and warming for respirators in which the problems of the magnetic components and the problems of electrical interference are avoided.

The solution according to the invention is characterized by the fact that it completely dispenses with magnetic components and uses a piezo pump for circulating the water.

The known piezoelectric effect is based on displacement of the spatial crystal structure of certain crystals and ceramics when an electrical voltage is applied. It is used industrially and commercially, especially for quick and accurate positioning, or as a linear drive for relatively slow processes.

The use as a pump was long unrealizable due to limited lifetime, poor efficiency, low flow. In most cases, the linear movement of the piezo element with mechanical elements was converted into a circular motion for motors.

According to the invention, it has now been found that, surprisingly, the piezoelectric effect can be used to drive the liquid pump of a respiratory gas humidifier. Recent developments in materials and technologies have mitigated all the above limitations. An industrially available piezo pump according to the so-called ultrasonic principle is provided by the company Nitto Kohki / Japan. Integrated electronics with this operating principle ensure a constant number of strokes at a given mains frequency and thus a constant delivery volume per minute.

According to the invention, it has now been found that such a piezo pump can be advantageously used in particular as a liquid pump in devices which are to be introduced into the magnetic field of an MR tomograph.

An essential feature of an embodiment of this invention düng is the integration of hollow fiber elements for humidification, water heating, hose heating, the piezo pump and sensors (pressure, temperature and lack of water) as a medical device for use in MRI and the combination with respiratory or anesthetic equipment, for. for adults or children and for combination with neonatal respirators and an MRI incubator while maintaining both MR compatibility and the constancy of physiological temperature and humidity in the respiratory gas.

In the following, the functional structure as well as delimitations and differences to conventional breathing gas humidifiers will be explained on the basis of advantageous embodiments with reference to the accompanying drawings, for example. Show it:

1 principle of the humidifier in block diagram (air and water flow) 2 shows the basic structure of an advantageous embodiment in conjunction with an MR incubator.

3 shows the basic structure of an advantageous embodiment as a stand-alone device;

4 shows an electrical circuit with source and drain;

FIG. 5 shows the circuit of FIG. 4 with a blocking filter; FIG.

Fig. 6 shows the frequency response of the notch filter of Figure 5;

Fig. 7a for fastening the Atemgasbefeuchters on the

MR-incubator suitable holder;

FIG. 7b shows the attachment of the ventilator to the holder and the attachment of this arrangement to the MR incubator; FIG.

FIG. 7c shows the attachment of the respiratory gas humidifier to the holder; FIG.

8 shows the display and operating interface for the humidifier integrated in the incubator control panel;

9 shows the stand-alone version of the humidifier; and

Fig. 10, the embedding of the electronic control and monitoring device in the humidifier.

The advantageous embodiment of the invention shown in Fig. 1 comprises a water reservoir 1, which contains a supply of water for the heating and humidification of the breathing air. This water is circulated through a liquid pump 2, which is designed according to the invention as a piezo pump. For this purpose, the temperature of the circulating water is first measured in a temperature measuring device 3, to which water is added from the water reservoir 1 when water is consumed. Behind the piezo pump 2, the water passes through a heat exchanger 4, in which it is electrically heated. Subsequently, it passes through a multi-lumen tube 5 in which the water circulates outside in the direction of the arrows 6, thereby heating the respiratory gas flowing through the inner lumen 7. The water and the respiratory gas flow through a measuring device 8 for water and breathing gas pressure, which are connected together with the other electronic components to a control circuit, not shown in Fig. 1. After passing through the measuring device 8, the water flows through a moistening module 9 and flows around a tube or tube 10 which is permeable to water vapor and through which the respiratory gas flows, which is thereby moistened. In a device 11 for detecting air bubbles, it is checked during continuous passage through the circuit system whether the system still has enough water.

The MR compatibility from the point of view of the electrical properties is generally achieved by spatial separation of the magnetically sensitive power supply unit (PSU in Fig. 2) from the non-magnetic piezo pump (included in PANFEUCHTER) and by the appropriate shielding of the electronic and electrical components. The connection cables required for this purpose are shielded and earthed, and the signals conducted in them are filtered. These measures are described in detail below. The system control SYSTEM of the incubator is used for setpoint input, the display of the actual values and any alarm messages.

The breathing gas humidifier according to the invention can also be used for other purposes, in Fig. 3, the stand-alone version is shown. In this case, the control panel is attached to the humidifier (SYSANFEUCHTER) itself and not to the incubator or to another control unit.

Achieving the electrical adaptation

i. Shielding: As a basic measure, the shielding of all involved components and their connections is carried out.

ii. Earthing: Each enclosing shield ends at a grounding point; the presence of ground loops impairs imaging and is therefore essential to avoid.

iii. Filtering: The third and most important measure is the filtering of the signals between PSU, SYSTEM and PANFEUCH. General: Each signal is between source (Q) and

Sink (S) along a path (usually an electrical cable) out, s. Fig. 2. The source is shown on the left side and the sink on the right. The frequency spectrums applied by the MRT are narrowband in the respective device class, so that by looping in a selective barrier filter of higher order along each signal path between PSU, SYSTEM and PANFEUCHTER, the above interferences are minimized. Such a notch filter can be easily realized as an LC element (2nd order passive filter) as shown in FIG. In the case of piezo technology, it is advantageous to note that in this application, the useful frequency range of the pump used (50 Hz or 60 Hz) is far enough away from that of the MRT (42-300 MHz) that the filtering does not cause any side effects. 4 shows the frequency response when using the notch filter according to FIG. 3. The resonance frequency was tuned for an MRT system with 1.5T magnetic field strength, this corresponds to a Lamor frequency of 63.9 MHz. In this range, the insertion loss is better than 40 dB. This filtering is now to be applied to each of the above-mentioned signal paths on both ends of the VKABEL and on the SYSTEM-side end of AKABEL.

NKABEL: Shielded power cable (3-core: L, N, PE) Length approx. 30 cm. (Already present in FIG. 2, being necessary as an AC supply cable for the incubator.)

POWER SUPPLY: Shielded box containing the switching power supply. Is spatially separated from the rest of the device and is operated in an area where the residual stray field of the MRI is very weak (flux density in the air B <20 Gauss). Thus, no impairment of the function of the switching power supply. (In Fig. 2 already exists, since as DC voltage generation (12V) necessary for the incubator.

PSTEUER: control electronics for the humidifier. This electronics is supplied directly from the power supply with 5V. The output via VKABEL are the power signals for the heat exchanger the input are the signals of the temperature sensors All lines of input and output are provided with a blocking filter of FIG. 3.

VKABEL: Shielded connection cable containing the cables described under POWER SUPPLY. This cable has a sufficient length (L = 4.5 m) to achieve the physical separation of the POWER SUPPLY from the device.

HUMIDIFIER: The humidification unit. The latter takes the power signals from the POWER SUPPLY and the control signals from the SYSTEM and sends the measured values back to the SYSTEM.

AKABEL: Shielded connection cable from the breathing gas humidifier to the SYTEM. Returns the power signals and the actual values of the sensors (temperature) and error messages back to the SYSTEM.

SYSTEM: The system electronics of the incubator. The signals arriving from the HUMIDIFIER are evaluated and displayed; in case of deviations, the user is alerted by the device.

Incidentally, the mains voltage and the DC voltage PANFEUCHTER and power supply are looped through and each provided with blocking filters according to FIG. 3.

Achieving mechanical adaptation

The drawings in Fig. 7 show stepwise the adaptation of the respiratory gas humidifier to the MR incubator. Basic connection element in Fig. 7a is the holder 12 made of the non-magnetic material aluminum. This holder has a fork-shaped geometry in order to be suitably plugged from above onto the operating part of the incubator 19, FIG. 7b. The knurled screw 17 serves for the fixation. The three bolts 16 serve to lock in the final position. With the four fastening screws 13, the ventilator 18 can be fastened from the rear side of the holder. The cutout 14 in the holder positively receives the front-side mounting plate 21 of the respiratory gas humidifier 20, Fig. 7c; 21, a force-locking connection is achieved with the spring preloaded draw bolt 15 and the matching bore in FIG. 21. Accordingly, the assembly also takes place from above, by pulling 15 the disassembly of the humidifier 20 can be initiated without additional tools, eg for an intended post-processing, cleaning or if the humidifier is not to be used for the application or examination.

The connection cable required for supply and control

(AKABEL in Fig. 2) between humidifier and incubator is not shown in Fig. 7 for the sake of clarity.

Achieving interaction with the user

The general system outlined in FIG. 1 is extended by FIG. 8 in terms of input-output elements to the user. In the first case, which belongs to FIG. 2, these elements are embedded in the already existing control panel 23 of the incubator.

The numerical display 29 is used to display the actual temperature of the heated breathing gas. The display 30 represents the user set and effective setpoint temperature. A change in this setpoint temperature is initiated by pressing the button 24; the adjustment (turning) as well as confirmation (pressing) of the new setting value is achieved by the rotary encoder 22 already present in the incubator. The signal lamp 25 indicates that the heating control circuit is active. The other indicators indicate that the humidifier is in an alarm state: The indicator light 26 is active in the context of alarms for which the corresponding sections must be observed in the operating manual; the signal light 27 indicates an empty water reservoir; the signal light 28 indicates an excessively high actual temperature relative to the setpoint; the signal light 31 indicates kinked hoses or other obstructions. All alarms are audibly sounded.

In the second case, Fig. 9 shows - the arrangement corresponding to the systematic structure in Fig. 3 - the stand-alone execution of the respiratory gas humidifier. Its front side is provided with a control panel according to FIG. 8, supplemented by the rotary encoder 33. The control and alarm concept corresponds exactly to that of the variant embedded in the incubator. For energy supply a sufficiently long supply line 34 (corresponding to VKABEL in Fig. 3) is used. The spatially remote (at least 2.5 m away from the MR magnet) power supply unit 35 (corresponds to the POWER SUPPLY in FIG. 3) and the power cable with plug 26 (corresponds to NKABEL in FIG. 3) complete the supply path.

Reaching the regulated breathing gas temperature

In Fig. 10, the block image described in Fig.l expanded by the required elements for temperature control. These can be roughly divided into the categories sensor, controller and actuators.

sensors: - The sensor for the actual value of the temperature is the thermistor (NTC) 37.

The pressure in the respiratory air path is measured with the electronic pressure sensor 39. The pressure in the water circuit is measured by the electronic pressure sensor 40.

- The detection of air bubbles (which corresponds to an insufficiently filled water cycle or lack of water) is achieved with the optical sensor 38, which is realized as a light barrier, applied to the transparent piece of tubing.

actuators:

- The manipulated variable as a controller output is the pulse width modulated (PWM) mains voltage (0 ... 100%), which is applied to the heating cartridge 41 and outputs a corresponding thermal power (0 ... 150W) to the heat exchanger.

The piezo pump 42 can be switched on or off to perform maneuvers such as Fill or rinse the humidifier.

controller:

- The control device 43 calculates the control variable (PWM) for the heater 43 from the difference between the actual and setpoint by means of a PID algorithm. In addition, alarm conditions are determined from the additional sensors 38 (air bubbles in the water circuit), 39 and 40 (pressure increase due to kinked hose). and the linearization of the thermistor characteristic curve. The user interface 44 serves as a source (setpoint input) and sink (measured value display, alarm display).

Claims

claims

A respiratory gas humidifier for heating and humidifying respiratory air with a humidification module (9) through which water and respiratory air streams are separated by water-permeable sheet-like elements, with a liquid pump (2) and a heater (4) ) for the water, characterized in that the liquid pump (2) is a piezo pump.

2. Breathing gas humidifier according to claim 1, characterized in that the moistening module (9) has a hollow fiber element (10).

3. breathing gas humidifier according to claim 1 or 2, characterized in that it contains a multi-lumen hose (5) for the separate guidance of the breathing gas and the water for hose heating.

4. Breathing gas humidifier according to one of claims 1 to 3, characterized in that it contains integrated sensors for temperature and pressure and has control devices.

5. Breathing gas humidifier according to one of claims 1 to 4, character- ized in that it contains an optical sensor (11) for the water shortage monitoring.

6. breathing gas humidifier according to claim 1 to 5, characterized in that the device is supplied in combination with the MR incubator via the incubator with power and the incubator contains the display and controls in the control electronics of the incubator.

7. breathing gas humidifier according to claim 1-6, characterized in that it contains matching and suitable mounting surfaces and elements with the incubator.

8. Breathing gas humidifier according to one of claims 1 to 5, characterized in that the device includes its own display and a stand-alone power supply.

9. breathing gas humidifier according to one of claims 1 to 8, character- ized in that it comprises a front of the liquid pump arranged temperature measuring means (3) for the recirculated water.

10. Breathing gas humidifier according to one of claims 1 to 9, character- ized in that it has pressure sensors (8) for the water and breathing gas pressure.

11. Breathing gas humidifier according to one of claims 1 to 9, characterized in that it comprises alarm means for reporting malfunctions.