DE9105742U1 - Measuring and calibration device for comparing measurement signals determined by means of pressure sensors implantable in the bodies of living beings - Google Patents

Description

181 G25

Measuring and calibration device for comparing measurement signals determined by means of pressure sensors implantable in the bodies of living beings

The invention relates to a measuring and calibration device for adjusting measurement signals determined by means of pressure sensors implantable in the bodies of living beings according to the preamble of claim 1.

In medical technology, sensors are often only used once for reasons of sterility. This applies in particular to sensors that are implanted in the human body and are intended to remain there for a certain period of time, for example. However, in order for the measurement to be carried out, each sensor or sensor must be equipped with calibration electronics, whereby the components for temperature compensation of the zero points and sensitivities as well as for compensation of the zero point and setting of the sensitivity are switched on individually. Since these amplifier circuits are usually outside the sterile application area, it would in principle be possible to use the amplifiers several times.

Another common approach is that the calibration components for a sensor are specified on a data sheet and these values must be subsequently set for the individual sensor in a preamplifier or in a device. However, since such settings usually require technical personnel and the nurses in hospitals usually do not have such technical skills, these solutions are often rejected as unusable.

The aim of the present invention is therefore to create a possibility of using sensors without calibration electronics in the medical field, whereby the calibration of the sensor should be able to be carried out without any problems even by untrained personnel. In addition, the possibility should be promoted that the processes and techniques that work using implantable pressure sensors can be used and implemented in practice much more comprehensively than is currently the case due to the extremely simple and uncomplicated operation of the measuring and calibration device, which is also inexpensive.

In principle, it should be possible to dispense with individual data being provided to each sensor. In individual cases, however, this may seem to make sense.

The object is achieved according to the invention according to the features specified in claim 1. Advantageous embodiments of the invention are specified in the subclaims.

The present invention creates an important improvement in the field of medical technology. According to the invention, it is now possible to calibrate a sensor in extremely simple and few steps, even by hospital staff who are largely untrained or untrained in the specific field of electronics. Above all, however, the measuring and calibration device according to the invention can always continue to be used, even if the

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Reasons once used measuring sensor is thrown away after use.

Finally, the measuring and calibration device according to the invention can also be used in parallel on several patients. It can be disconnected from a sensor implanted in the human body, for example, and connected to the next sensor.

In a particularly preferred embodiment, both a reference sensor provided according to the invention and a pressure regulator are integrated in the device according to the invention.

Overall, the inventive design of the device allows both financial and application advantages to be achieved.

Further details, features and advantages of the invention will become apparent from the following description of the invention, illustrated by means of drawings.

Example of implementation. Shown in detail: 20

Figure 1 : a block diagram with the essential components

of the measuring and calibration device according to the invention;

Figure 2: a schematic functional representation of the device;

Figure 3 : a block diagram of the device according to the invention

in a first embodiment;

Figure 4: a variation of Figure 3.

Figure 1 shows the measuring and calibration device according to the invention in a top view with a display 1, an on/off switch 3, a "zero" switch 5 and a "calibration" switch 7. The switches or keys shown belong to an input keypad 4.

As is not shown in detail in Figure 1, a first interface 11 in the form of a connector is provided on the housing 9, to which an external sensor 13 for use in the medical field can be connected.

In the embodiment shown, for example, there is a piezoresistive pressure sensor 13 with an external measuring point 13' and a reference pressure measuring point 13" located on the inside of the measuring membrane, i.e. the back of the measuring membrane 15. The measuring point 13' and the reference pressure measuring point 13" are therefore hermetically separated from one another.

The reference pressure measuring point 13" is connected via a reference pressure channel 17 to a reference sensor 19 integrated in the device and via a branch line to a pressure sensor 21, for example in the form of a pump. Finally, electrical connection and measuring lines 23 are also provided, via which the external sensor 13 can be connected to the electrical and electronic systems of the measuring and calibration device.

At the interface 11, the part of the reference pressure channel 17 located outside the device, for example in the form of a hose or catheter, can be connected via a suitable connector plug 12 together with the electrical connection and measuring lines 23, which also run in an outer casing 25, and can be disconnected again at any time if required.

The pressure sensor 21, which is preferably designed in the form of a miniature pump and integrated in the device, is shown in Figure 2 in its one end position A, in which the ambient pressure 29 acts directly into the reference pressure channel 17 via a bypass 27. If the pump, i.e. in the embodiment shown the piston, is moved to the right into its position B via a suitable actuating element 31 in the piston housing, the ambient pressure 29 is cut off and a pressure lower than the ambient pressure is built up inside the reference pressure channel (which will be discussed later).

The electronics of the measuring and calibration device also include - as can be seen in particular from Figure 3 - a sensor processor 35 and a microprocessor 37. Both the reference sensor 19 and the implantable external sensor 13 are connected to the sensor processor.

The sensor processor 35 is directly connected to the microprocessor 37 in terms of circuitry and function. The microprocessor is controlled via the input and keypad 4. The display 1, which is preferably designed as a digital display, is also controlled via the microprocessor 37 like the keypad 4. Finally, a digital/analog converter 39 can also be provided in order to display an analog signal on the display panel 1 and/or to use this to place a corresponding analog signal on an analog output 41 to which a monitor can be directly connected. The so-called sensor processor 35 is therefore a link between the measuring pressure sensor 13 or the reference pressure sensor 19 and the microprocessor (μ�R) 37, whereby the sensor processor 35 essentially consists of an analog-digital converter. The analog measurement signals are digitized via it, whereby the sensor processor 35 can have a so-called multiplexer integrated for cyclical querying of the pressure signals generated by both the reference pressure sensor 19 and the measuring pressure sensor 13. The analog measurement signals can be processed in digitized form in the microprocessor 37 using the A/D converter in the sensor processor 35. The sensor processor 35 is connected to the microprocessor 37 via a bidirectional bus, for example to control the multiplexer mentioned above integrated in the sensor processor 35.

In order to calibrate an implantable sensor, e.g. an intracranial sensor for measuring brain pressure, such an external sensor 13 is connected to the measuring and calibration device 1 according to the invention before the operation, i.e. before the implantation. The pump is first brought into its first end position A shown in Figure 2. Since in the

End position A of the pump, the ambient pressure is present not only at the outer measuring point 13', but also at the rear reference pressure measuring point 13", the so-called zero point signal of the measuring pressure sensor 13 can be determined in this position of the pump, i.e. of the pressure transmitter 21. The value can be, for example, 6 mV. This value is then stored in the microprocessor or in another memory and later taken into account in all measurements taken by the implanted sensor in the sense of compensation, i.e. deducted.

The pressure sensor 21 is then set to at least a second position, e.g. position B. This can be done by adjusting the actuating member 31 shown in Figure 1, for example, which protrudes onto the top.

This cuts off the external ambient reference pressure and creates a pressure of, for example, 200 mbar, which is generated by the position of the pump. This pressure value is present at the reference pressure sensor 19 and at the reference pressure measuring point 13" of the externally connectable pressure sensor 13. The reference pressure sensor 19, also referred to as the reference sensor for short, measures this pressure and transmits this pressure via the sensor processor, also referred to as the process controller 35 for short, to the electronics of the microprocessor 37, which registers this pressure. The signal from the measuring pressure sensor 13 is also passed on to the microprocessor 37 in digitalized form via the process controller 35. The microprocessor 37 records these two pressures. Since it knows the pressure from the reference pressure sensor 19, it gives the measuring pressure sensor 13 the corresponding amplification, i.e. sensitivity factor, so that it is correctly calibrated. This new signal calculated by the microprocessor can then also be shown on the digital display 1. From the signal of the measuring sensor 13, the correct sensitivity for the desired output signal is calculated. For example, if the pressure signal of the measuring pressure sensor 13 is 80 mV and the corresponding value of the reference pressure sensor 19 is to be 100 mV, the microprocessor 37 calculates the amplification or the

Sensitivity factor of 1.25, with which all measured values of the measuring pressure sensor 13 are then multiplied. The adjustment is therefore carried out in the sense of a multiplicative setting of the gain/sensitivity factor by comparing with the corresponding value of the reference pressure sensor 19 and by taking into account a sign-dependent addition with the corresponding signal value for the zero point of the measuring pressure sensor 13. The sensitivity/gain factor is also stored in the microprocessor 35 or in another memory. During use of the measuring sensor in the implanted state, the stored adjustment values are then processed by software.

The adjustment can be carried out, for example, in position A of the pressure sensor 21 simply by pressing the adjustment button 7.

After pressing, the zero point of the measuring pressure sensor 19 is automatically determined and saved as explained above. After determining and saving the zero point value for the measuring pressure sensor 13, the message "GO TO P" appears on display 1 at the same time. This means that a reference pressure that differs from the ambient pressure should now be set. After that, a pressure that differs from the ambient pressure only needs to be set on the pressure sensor, for example by moving the pump to position B. As soon as the pressure set afterwards is stable, the electronics can automatically determine the corresponding signals from the reference pressure sensor 19 and the measuring pressure sensor 13 and set and save the gain/sensitivity factor by comparing them.

It would also be possible that the adjustment of the gain factor is not carried out automatically after a stable reference pressure is present, but after pressing the adjustment button 7 again.

In such an embodiment, the zero button 5 would have the function of short-circuiting the measuring pressure sensor 13.

This allows the zero point characteristic curve of the measuring pressure sensor 13 to be determined with a monitor connected to the analog output 41.

In this way, a well-defined position of the measuring sensor can be quickly adjusted by simply pressing a button and operating a pressure sensor (pump).

Deviating from the calibration procedure explained above, a two-button calibration would also be possible in such a way that first of all, after pressing the zero button 4, the zero point signal of the measuring pressure sensor 13 is determined and stored, and after setting a reference pressure that differs from the ambient pressure, after pressing the calibration button 7, the gain sensitivity factor for the measuring pressure sensor 13 is determined and stored.

The calibration values of the connected measuring sensor remain in the memory of the electronic device until a new measuring sensor is connected.

Alternatively, the device can be provided with a larger memory in which, for example, up to 10 sensor values can be stored. When the measuring device is alternately connected to different sensors, for example those implanted in the human body, the previously stored sensor values can be automatically retrieved without having to carry out a new calibration.

Using the measuring and calibration device described above, individual gain and zero point compensation values can be determined for an externally connected sensor in a very simple and cost-effective manner.

For certain applications, the output signal must also be able to follow dynamic pressure curves. If the signal is fed via the process controller 35 and the microprocessor 37 via the di-

gital/analog converter 39 to the analog output 41, only about 2 to 5 measurements can be transmitted per second, which is too few for dynamic applications.

In a modified version according to Figure 4, an additional programmable amplifier 43 is therefore provided. In a modification to Figure 3, the external measuring sensor 13 is controlled by the programmable amplifier 43 and is connected to it, whereby the programmable amplifier 43 is functionally connected to the keypad 4, the sensor processor 35 and, above all, the microprocessor 37, through which it receives the pressure signals from the reference sensor 19 via the downstream sensor processor 35. In this version, the signal from the externally connectable measuring sensor 13 is routed to the programmable amplifier 43. The signal from the output of the programmable amplifier 43 is routed to the analog output 41.

The microprocessor 37 controls the programmable amplifier via software so that the output signal is calibrated to the correct magnitude. The zero point signal is also programmed into the programmable amplifier 43 in this way. The calibration is carried out in the same way as explained using the example shown in Figure 3. In this way, however, signals up to 5 kHz and higher can also be read out at the output of the programmable amplifier 43.

The figures explain how, in the medical field, a pressure sensor that is to be implanted in the human body, for example, can be easily adjusted and calibrated without detailed knowledge of its functional data. This makes it possible to easily implant pressure sensors, for example as brain pressure sensors, after adjustment in order to be able to measure intracranial pressure (ICP).

The probe can be placed epidurally, for example, i.e. between the skullcap and the dura (outer membrane of the brain).

The probe placed in this way can usually remain implanted for up to 10 or 12 days.

The device according to the invention is also equally suitable for calibrating sensors which can then be used in the body, for example, to measure bladder pressure, muscle compartment pressure, ventilation pressure in the lungs, etc. and then usually remain implanted for hours and days.

In the implanted state, the ambient pressure is present on the rear side of the measuring pressure sensor 13 when the pump is in the end position A. In principle, even in the implanted state of a sensor, the functionality of the sensor could be checked by, for example, setting different reference pressures and determining the strength of the output difference signal between the two different pressures and comparing it with the theoretical value.

Claims (13)

181 G Claims: 1. Measuring and calibrating device for adjusting pressure sensors (13) that can be implanted in the bodies of living beings, which, in addition to a first pressure measuring point (13'), comprise a further reference pressure measuring point (13") that is hermetically sealed therefrom, which can preferably also be pressurized with a reference pressure via a reference pressure channel (17) in the implanted state of the pressure sensor (13), with a further reference pressure sensor (19), which can also preferably be pressurized with the reference pressure that can be applied to the reference pressure measuring point (13") of the pressure sensor (13) via the reference pressure channel (17), with a pressure transmitter (21) via which at least two different reference pressures can be set, and with electronics (35, 37, 43) in such a way that at a first preselectable reference pressure, preferably the ambient pressure, the zero point signal of the pressure sensor (13) can be measured or a corresponding previously known Zero point signal value of an individually connectable pressure sensor (13) can be entered and stored and, at a second reference pressure that can be preselected and differs from the first pressure point, the amplification/sensitivity factor of the measuring signal of the pressure sensor (13) can be adjusted depending on the calibrated pressure signal of the reference pressure sensor (19). 2. Measuring and calibrating device according to claim 1, characterized in that the pressure sensor (21) is preferably integrated in the device in the form of a miniature pump. 3. Measuring and calibration device according to claim 1, characterized in that an external pressure sensor (21) can be connected to an interface of the device to the reference pressure channel (17) extending from the interior of the device. 4. Measuring and calibrating device according to one of claims 1 to 3, characterized in that the pressure sensor (21) can be switched over to at least two end positions for generating different pressures, wherein preferably in one end position the ambient pressure is present in the reference pressure channel (17). 5. Measuring and calibration device according to one of claims 1 to 4, characterized by a microprocessor (37) and preferably a further sensor processor (35) associated at least with the reference sensor (19), which comprises an analog/digital converter. 6. Measuring and calibrating device according to one of claims 1 to 5, characterized in that a preferably programmable amplifier (43) is also provided. 7. Measuring and calibration device according to claim 6, characterized in that the preferably programmable amplifier (43) is assigned to the pressure sensor (13). 8. Measuring and calibration device according to claim 6 or 7, characterized in that an analog output (41) is provided on the programmable amplifier (43). 9. Measuring and calibration device according to one of claims 1 to 8, characterized in that the device has a resolution with respect to pressure fluctuations at least at a level of 100 Hz, at least 500 Hz, 1,000 Hz, 2, 3, 4 or at least 5 kHz. 10. Measuring and calibration device according to one of claims 1 to 9, characterized in that a digital/analog converter (39) is also provided, preferably controlled by the microprocessor, the output signal of which is at least indirectly available at a separate analog output (41). 11. Measuring and calibration device according to one of claims 1 to 10, characterized in that at least two display fields are provided on which the corresponding measuring and/or calibration signals and/or values are displayed once for the reference pressure sensor (19) and the externally connectable pressure sensor (13). 12. Measuring and calibration device according to one of claims 1 to 11, characterized in that an interface (11) for connection an external catheter (25) is provided, via which the external pressure sensor (13) with the part of the reference pressure channel (17) running in the catheter and the associated measuring and/or connecting lines (23) can be connected to the device. 20 13. Measuring and calibration device according to one of claims 1 to 12, characterized in that an electrical energy supply, preferably a rechargeable battery, is provided in the device.