DEVICE FOR MONITORING AND DISPLAYING CARDIAC RHYTHM

Abstract: The equipment has a signal generating amplifying unit (10), that can provide a signal of polarity corresponding to the polarity of the major ECG wave (R) or waves (R, S) observed at the output of the signal generating amplifying unit (10), further it has a signal shaping circuit (20) connected to the first output of the signal generating amplifying unit (10) as well as a clock-signal generator (32) provided with a control input, a first counter (30) provided with parallel outputs, counting the clock signals emitted by the clock-signal generator (32), and has LED displays (41 ... 50) connected to definite outputs from among the parallel outputs of the first counter (30), the output of the signal shaping circuit (20) is connected to the other terminal of the LED displays (41 ... 50) either directly or with a driver circuit (36) inserted, and, with a starting circuit (34) inserted, to the enabling input of the first counter (30) and to the synchronising input of the clock-signal generator (32).

Description: Device for monitoring and displaying cardiac rhythm The subject of the invention is an equipment for monitoring and displaying cardiac rhythm and cardiac frequency both for general use and as an equipment in therapy, mainly as a diagnostic aid or, in certain cases, as a medical equipment. The said equipment has a signal generating amplifying unit with inputs that can be coupled to sensing electrodes, and a display. The contraction of the heart is known to be elicited by the appearance of action currents. In a healthy human body the action potential changes eliciting action currents follow one another almost periodically. The frequency of action potential changes depends on the degree the heart is loaded, under average load the cardiac frequency is mediocre, when at rest, under stress, in response to physical loading etc. the beating becomes gradually faster or slower according to the amount of blood required. When the periodicity changes, when a period substantially deviates from the expected one, for instance it becomes 0.25 s longer or shorter, a typical symptom of operational trouble, i.e. arrhythmia occurs, which usually remains unnoticed by the person in question unless he or she pays special attention to it. Consequently, monitoring the periodicity of cardiac function may be used for predicting pathological changes in the rhythm of the heart and thus it may be a method of preventing certain disease. So, in order to maintain health, it may be desirable at certain persons to monitor the periodicity of cardiac function and/or the occurrences of change in the frequency together with the extent of changes in period length in cases of changed frequency. ECG is a known equipment to monitor and record cardiac f nctions. It records the changes in time of action potentials eliciting the functioning of the heart, and provides data on cardiac frequency, on the state of the cardiac muscle and its blood supply, etc. It is a further characteristic of the equipment, that in order to obtain more exact result when measuring cardiac frequency, it measures the lengths of a definite number of periods (at least four, depending on the make) and it displays the average of the four values as the value measured for one length, then it calculates the next average from subsequent periods of the given number while displaying the former value. The disadvantage of this method is that a change in the length of one period does not essentially influence the average value displayed, consequently the arrhythmic function and its degree cannot always be determined with full certainty directly from the quantitative value of the cardiac frequency displayed. The structure of the equipment is complicated, it requires professional skills to operate it and, owing to the large amount of exact data it provides, proper use of it can be made only under the control of a medical practitioner, and also its price is rather high. Another known device is the Holter device, which uses three to four electrodes placed on suitable spots to sense and measure the action potentials. It compares the measured values with the values of the ideal ECG signal stored in its memory, and if it finds difference exceeding a prescribed level, it stores the deviating value, actually the values of the period characteristic of arrhythmic cardiac function, together with the time of measurement. The values stored can be read at the time of evaluation with the help of a reading device. A Holter device is not suitable for simultaneously displaying a short cardiac disorder. Even its variants designed to provide the most service will only signal the fact of deviation simultaneously, that is, it only alarms but gives no information e.g. as to what the deviation actually is, and what is to be done. The equipments described above have the following disadvantages: they are either very expensive and their application requires professional skills, or they are not suitable for the simultaneous signalling of functional troubles (subjective complaints) occurring from time to time left unnoticed by the person in question because they are rare and short, which can be considered as premonitory signals of later complaints (like pain, breathlessness, cardiac infarct etc.), manifested in the changing of the length of some periods or in the distortion of a characteristic wave, especially R and/or S wave, therefore these equipments are not suitable for preventing later complaints or making them avoidable. The demand for observing and displaying cardiac rhythm as well as the shortcomings of the equipments used for this purpose call for creating an equipment suitable for real time monitoring and displaying cardiac rhythm, especially for signalling the rare occurrence of some periods deviating from the normal one with more than a predetermined limiting value, and the approximate value of the difference. At the same time the structure of the equipment is simple, it is not expensive to manufacture, its handling requires no professional skills, it can be widely applied either for general use and in therapy, mainly as a diagnostic aid and as a medical equipment in certain cases. It is also required that the equipment should be able to impart information not only to the person in question but also to a supervising individual at a distance of a few meters. It was also a requirement that the equipment should be able to control the functional range of frequency of a healthy heart. The basic idea of the invention is that the equipment should be able to measure the length of the period between the occurrence of the main electric impulses generated by the heart, conveniently the period between the occurrences of the R-waves, and to display the value measured simultaneously with displaying whether the duration of the period was normal, providing thus even non-expert users with proper information without having to evaluate the data displayed, while the equipment is also able to provide specialists with sufficient pieces of information for diagnostics, therapy and rehabilitation at the same time. The equipment representing the solution of the problem, suitable for monitoring and displaying cardiac rhythm (cardiac frequency) has a signal generating amplifying unit with inputs that can be connected to sensor electrodes and a display. The essence of the equipment is that it provides a signal of polarity corresponding to the polarity of the major wave (R) or waves (R,S) of the changes in the action potential observed at the output of the signal generating amplifying unit, it also has a signal shaping circuit connected to the first output of the signal generating amplifying unit as well as a clock-signal generator provided with a control input, a first counter provided with parallel outputs, counting the clock signals emitted by the clock- signal generator, and has LED displays connected to definite outputs from among the parallel outputs of the first counter further the output of the signal shaping circuit is connected to the other terminal of the LED displays either directly or with a driver circuit inserted, and, with a starting circuit inserted, to the starter input of the first counter and to the synchronising input of the clock-signal generator. At an advantageous embodiment of the equipment a first oscillator is connected to the output terminal of the signal shaping circuit, and a sound emitter is coupled directly or indirectly to the output terminal of the oscillator. At an advantageous realisation of this embodiment the first oscillator is coupled to the first output terminal of the signal shaping circuit with a first switch inserted. It is an especially favourable embodiment where the first counter has an overflow output and an overflow indicator coupled to it. The embodiment of the equipment according to the invention designed for general use has an OR logic function circuit, an AND logic function circuit connected to the output terminal of the OR logic function circuit by its first input terminal, and a second counter coupled to the output terminal of the AND logic function circuit by its input terminal, where the input terminals of the OR logic function circuit are coupled to some of the output terminals of the first counter, conveniently to not privileged terminals, and the second input terminal of the AND logic function circuit is coupled to the output terminal of the signal shaping circuit. At another version of this embodiment sensing distortions of the wave of other polarity (S) as well, the signal generating amplifying unit has a second output terminal coupled to the input terminal of the second counter. It is a preferable embodiment where a second oscillator, reasonably tuned to a frequency other than the frequency of the first oscillator, is coupled to the output terminal of the second counter, and the output terminal of the second oscillator is coupled to the input terminal of the sound emitter, and the output terminal of the second counter is coupled to its count disabling input terminal. More effective acoustic signal can be established at an embodiment where the output terminal of the first oscillator and the output terminal of the second oscillator are connected to the input terminals of a summing circuit, and the output terminal of the summing circuit is coupled to the input terminal of the sound emitter. A further advantageous embodiment has a timing generator, and the output terminal of the timing generator is coupled to the resetting input terminal of the second counter. At this embodiment the timing generator has a timing element or timing elements, suitably timing capacitor (s) that can be connected or disconnected by a time-span selecting switch. It is a favourable embodiment where the overflow output terminal of the first counter is coupled to the input terminal of the second oscillator. An intensive warning acoustical signal can be provided at a solution where the output terminal of the timing generator is coupled to the resetting input terminal of the second counter with a controlled switch inserted, and the control input terminal of the controlled switch is coupled to the overflow output terminal of the first counter. At a favourable embodiment the equipment has a manual switch, preferably a push button, inserted between the zero setting input terminal of the second counter and/or the timing generator and a terminal of appropriate potential. The signal generating amplifying unit of the equipment according to the invention has an input differential amplifier preferably coupled to the sensing inputs with its input terminals, a level adjusting amplifier coupled to the output terminal of the input differential amplifier through an amplifier and an separating capacitor, furthermore a double signal shaping circuit coupled to the output of the level adjusting amplifier through a filter, suitably an active filter, preferably an active narrow band filter, a level amplifier and a capacitor, where the outputs of the double signal shaping circuit constitute the outputs of the signal generating amplifying unit. The essence of the equipment according to the invention is now described in detail in connection with a preferable embodiment, with reference to the accompanying drawings in which: Figure 1. shows the basic block diagram of the construction of an embodiment of the equipment providing a wide range of services, Figure 2. shows a favourable example block diagram of the signal generating amplifying unit of the equipment, Figure 3a. shows a time profile of the signal shape in case of arrhythmic operation of the heart; Figure 3b. shows the shape of the signal appearing on the first output of the signal generating amplifying unit in case of sensing the signal indicated in figure 3a., Figure 3c. shows the shape of the signal appearing on the output of the signal shaping circuit in case of sensing the signal indicated in figure 3a., Figure 4a. shows a time profile of the shape of the signal m case of cardiac action with a certain type of anomaly, Figure 4b. shows the shape of the signal appearing on the first output of the signal generating amplifying unit in case of sensing the signal shown in figure 4a., Figure 5a. shows a time profile of the shape of the signal in case of cardiac action with another type of anomaly, Figure 5b. shows the shape of the signal appearing on the first output of the signal generating amplifying unit in case of sensing the signal shown in figure 5a., and Figure 5c. shows the shape of the signal appearing on the second output of the signal generating amplifying unit in case of sensing the signal shown in figure 5. a. As can be seen in " Figure 1, the equipment has a signal generating amplifying unit 10 with sensing inputs 1, 2 and 3 which are couplable to sensor electrodes, mostly silver - silver chloride electrode bonds attached to the body of the person to be examined. A signal shaping circuit 20, comprising of a Schmitt trigger is coupled to the first output terminal of the signal generating amplifying unit 10, a possible embodiment of which can be seen in Figure 2. The first branch of the output of the shaping circuit 20 is coupled to the input terminal of a starting circuit 34, which is a differentiating circuit in this example. The starting circuit 34 is coupled to the synchronising input of a clock- signal generator 32 and to the starter input of a first counter 30. The output terminal of the clock-signal generator 32 is coupled to the input terminal of the counter 30. The clock-signal generator 32 of this example emits clock signals every 200 ms, counted by the counter 30. The counter 30 is fashioned in a way that on their parallel outputs from 1 to 10 the output bearing the serial number corresponding to the number of the impulses counted rises to active level. LED displays 41, ...43, 44, 45 ... 50 are connected to certain parallel outputs of the counter 30, in our present case to all of them. The LED coupled to the privileged output (in the present example it is LED 44) is green, while the other LED displays coupled to non privileged outputs has other colour, favourably they are red. The other - connected - terminals of LED displays 41 50 are coupled to the output terminal of a 10 driver circuit 36 connected to the first branch of the output terminal of the signal shaping circuit 20. The counter 30 has an overflow output terminal, and an overflow indicator 38 which is coupled to it. A first oscillator 24 is coupled to the second branch of the output terminal of the signal shaping circuit 20 through a manually operated first switch 22. The output terminal of this oscillator 24 is coupled to the input terminal of a sound emitter 28 through a summing circuit 26. The non-privileged outputs from the parallel outputs of counter 30 are tapped and coupled to the input terminals of an OR logic function circuit 52, in this case it is an OR gate circuit. The output terminal of this OR logic function circuit 52 is coupled to one of the input terminals of an AND logic function circuit 54, in this case it is an AND gate circuit. To the other input terminal of the AND logic function circuit 54 the third branch of the output terminal of the signal shaping circuit 20 is connected. The output terminal of the AND logic function circuit 54 is coupled to the input of a second counter 60, the output of counter 60 is coupled partly to its own count disabling input and partly to the input of a second oscillator 70. The output terminal of oscillator 70 is coupled to the other input terminal of the summing circuit 26. Further, the equipment has a timing generator 66, its output is coupled to the resetting input of counter 60 through a 11 controlled switch 56. The controlling input of switch 56 is coupled to the overflow output of the counter 30. Timing generator 66 is a variable timer, it has a timing defining first timer capacitor 64 and a second timer capacitor 65. By connecting one of them into the circuit of the timing generator 66 using a time-span selecting switch 62, the desired timing can be set. The overflow output of counter 30 is coupled to the other input of oscillator 70 as well. Further, the equipment has a push button switch 58, in this case it is inserted between the timing generator 66 and the zero adjuster input terminal of the second counter 60 and a terminal of appropriate potential. Figure 2 shows the block diagram of an example of the signal generating amplifying unit 10. It can be seen that the signal generating amplifying unit 10 has an input differential amplifier 11 coupled to the sensing inputs 1, 2 and 3 by its input terminals and, in addition, a level adjusting amplifier 14 coupled to the differential amplifier's output through an amplifier 12 and an separating capacitor 13. A double signal shaping circuit 18 is coupled to the output of the level adjusting amplifier 14 with a narrow-band active filter 15, a level amplifier 16 and a capacitor 17 inserted. The double signal shaping circuit 18 has two high-gain amplifiers, one of them amplifying the signal components of one polarity, the other one amplifying the signal components of the other polarity, and has two separate output terminals for 12 outputting positive and negative signals. These output terminals constitute the output terminals of the signal generating amplifying unit 10 at the same time. During operation, this embodiment receives the electric signal of 1-2 mV generated by the heart according to curve P- Q-R-S-T at its sensing inputs 1, 2 and 3. The differential amplifier 11 and amplifier 12 amplify the signal received together with the superimposed noise signals, the separating capacitor 13 cuts the direct current component. We can set the zero-level of the signal with the level adjusting amplifier 14. The active filter 15 separates the noise signals from the signal according to curve P-Q-R-S-T, and the resulting signal is amplified to a level of 2-3 V amplitude by the high-gain level amplifier 16. The true-to-shape signal filtered this way and amplified to the required level is further amplified by the signal shaping circuit 18 applying overdriven amplification. In case of a normal P-Q-R-S-T curve, the first output of the signal shaping circuit 18, which is the first output of the signal generating amplifying unit 10 at the same time, provides a trapezoidal signal the width of which corresponds to that of the R wave, and the second output of the signal shaping circuit 18, which is the second output of the signal generating amplifying unit 10 at the same time, it provides zero signal-level. If the cardiac disorder causes enlargement of the S wave, a trapezoidal signal will appear at the second output as well, with its width corresponding to that of the S wave. From the signal appearing at the first output terminal of the signal generating amplifying unit 10, the signal shaping 13 circuit 20, which is a comparator having hysteresis, which is a Schmitt trigger and a timing circuit in the present case, creates a signal with its width proportional to the width of the R wave. The signal created from it by the starting circuit 34, which is a differentiating circuit in the present case, enables counter 30 to reset to zero and to start counting from zero, and also starts the clock-signal generator 32 synchronised. Counter 30 keeps counting the outgoing signals of the clock-signal generator 32 until the signal originating from the next R wave elicits counter 30 to reset to zero and start counting again. With a regular heart frequency the next R wave arrives after an interval of app. 800 ms . During this period of time the clock-signal generator 32 emitted four clock signals, thus counter 30 counted four, consequently its fourth parallel output is activated resulting in forward voltage on the green LED diode 44 coupled to the fourth parallel output as privileged output. As a consequence of the voltage provided by the driver circuit 36, the green LED diode 44 is lit indicating that the last measured periodical time of the heart action was within the set limits. If the heart frequency is not the normal, counter 30 counted less or more than four, depending on whether the heartbeat was faster or slower. As a result, an other, non-privileged output of counter 30 will be activated, and a not green, usually red, LED diode connected to it, e.g. LED 43 or 45 is lit, warning that the heart frequency is deviating from normal. The equipment can be set to signal every electric impulse eliciting contraction of the heart, practically every heartbeat acoustically. In this case the first switch 22 is 14 closed, and the signal received from the output of the signal shaping circuit 20, the length of which signal is determined by the length of the R wave, operates the first oscillator 24, and the sound emitter 28 gives a definite first frequency sound signal for the duration of the signal. If the equipment does not sense a new R wave after an R wave for a period of time determined by the capacity of counter 30 and the frequency of the clock-signal generator 32, the counter 30 overflows. The equipment signals failure of the arrival of an R wave in two ways. An overflow indicator 38, which is a further LED diode is operated. At the same time, it alarms by enabling the second oscillator 70, coupled to the overflow output terminal of counter 30 and set to a second frequency, and operating the sound emitter 28 via the second oscillator 70 on the second frequency, giving a different, continuous sound signal. If the equipment signals the absence of R wave by a continuous signal, and it receives an R wave again, and the switch 22 is closed, the sound emitter 28 emits a third frequency acoustic signal for the duration of the R wave, created by the summing circuit 26 from the outgoing signals of the first and the second oscillator 24,70 of different frequencies, indicating that cardiac action continues after the interruption. The second counter 60 counts the rate of the appearance of irregularities in the periodicity of cardiac action. The OR logic function circuit 52, coupled to the non-privileged output terminals of the counter 30 by its input terminals 15 collects the signals appearing on some of the non-privileged output terminals of counter 30, activated in case of periods of irregular length. Then these signals indicating irregularities in periodicity are coupled to the AND logic function circuit 54 gated with the outgoing signal of the signal shaping circuit 20 and are entered into counter 60. Counter 60 records these signals as irregular events. The second output terminal of the signal generating amplifier 10 emits a signal when the S wave is deformed (so called ST sank) . This outgoing signal, referring to the occurrence of an irregular event, will be entered into counter 60 directly. With its second input terminal, oscillator 70 is coupled to the output terminal of counter 70 counting irregular events, thus, when the number of irregularities reach the value set by programming counter 60, the equipment emits continuous sound signal by operating oscillator 70, and simultaneously, counter 60 is reset by feeding back the output of it. The monitoring or examination time span for keeping track of the frequency of irregularities can be set. The timing of the timing generator 66 can be set by the selection and insertion of timer capacitor 64 or timer capacitor 65 by the time-span selecting switch 62. When the timing period is over, the reset signal, emitted by the generator 66 resets counter 60 to zero through the controlled switch 56. Further, the equipment has a push button switch 58 connected to a terminal of suitable potential, by which generator 66 can be restarted and counter 60 can be reset. 16 The controlling input of switch 56 is coupled to the overflow output terminal of counter 30, preventing counter 60 to be reset during overcharge is indicated. This makes it possible to determine the number of irregular events occurred in the period preceding the stopping of cardiac frequency in case if the electric operation of the heart stopped during examination and re-starting was not occured during the examination period. Figure 3a shows time profile of regular shaped P-Q-R-S-T signals. As it can be seen in the figure, the time the impulses follow each other varies, in the case shown in the figure the first periodical time is normal, the second period is longer than the normal period, and the third period is shorter than the normal period. Figure 3b shows the outgoing signals of the signal generating amplifying unit 10, figure 3c shows the outgoing signals of the signal shaping circuit 20 in case of signals according to figure 3a. Comparing the figures, it can be seen that the signals generated by the signal shaping circuit 20 are increased with time T, making it possible to obtain signals of required parameters for operating the further circuits even in case if the signals received are very narrow. With the signals of periodical times according to the figure, at the end of the first period the green LED 44 of the equipment is lit, in response to the next signal received, red LED 45 indicating an increased period is lit, and in response to the next signal received, red LED 43 indicating a shorter period is lit. 17 Figure 4a shows a signal shape indicating irregular action, so called ST wave raised. Figure 4b shows the outgoing signals of the signal shaping circuit 20 in the response to signals according to figure 4a. As a consequence of the widening of the R " wave, the flash signal and the acoustic signal emitted by the apparatus are longer, the number of subsequent LED displays lit is the same as the times the width of the RST wave is longer than the periodic time of a clock signal. Hence, even though the cardiac frequency has not changed, the equipment indicates irregular cardiac action. It is important in cases when the cardiac frequency is not changed, but the RST wave is widened due to e.g. an anginal attack. Figure 5a shows another signal shape indicating a different sort of irregularity, so called ST sank. Figure 5b displays the outgoing signals of the signal shaping circuit 20 in response to signals according to figure 5a. It can be seen that due to the relatively normal shape of the R wave, the LED displays indicate operation with normal periodical times. Figure 5c shows the signal shape appearing on the second output of the signal generating and amplifying unit 10, which signal is a wide negative impulse, not the zero-level appearing in case of regular operation. The equipment registers this shape referring to anomaly by counting with counter 60. A major advantage of the equipment according to the invention is that it provides essential information for both the person using the equipment and/or the person observing the person using the equipment. 18 It is a further advantage of the equipment that the sensor electrodes can be placed to any usual spots of the human body, e.g. to the chest or to the limbs, the equipment provides valuable " information. It is still another significant advantage of the equipment that that it measures and displays the periodical time of every single cycle of the cardiac action, displaying the cardiac frequency measured in the given period (i.e. the limiting values of the measured cardiac frequency) , indicating this way the state of the heart at the moment, and informs by light or sound or by alarm signal, depending on the need. This way the equipment is especially suitable for checking the actual working capacity of the heart of a healthy, sick or recovered patient at any time, and for signalling possible prodromes of a heart failure. This way it offers better chance to prevent such trouble and to monitor the effectiveness of follow-up care as well as to monitor recovery.

Claims: 19 Claims : 1./ Equipment for monitoring and displaying cardiac rhythm, having a signal generating amplifying unit with inputs that can be coupled to sensing electrodes, and a display characterised in that it can provide signals with polarity corresponding to the polarity of the key wave (R) or waves (R, S) of the action potential change received at the output of the signal generating amplifying unit (10), further on it has a signal shaping circuit (20) coupled to the first output of the signal generating amplifying unit (10) , a clock-signal generator (32) with a control input, a first counter (30) with parallel outputs so as to count the clock- signals generated by the clock-signal generator (32), and LED displays (41,....50) coupled to definite outputs from among the parallel outputs of the first counter (30) , the output terminal of the signal shaping circuit (20) is coupled directlv or through a driver circuit (36) to the other terminal of the LED displays (41,.... 50) and, through a starting circuit (34), to the starter input terminal of the first counter (30) and to the synchronising input terminal of the clock-signal generator (32). 2./ The equipment according to claim 1 characterised in that a first oscillator (24) is coupled to the output terminal of the signal shaping circuit (20), and a sound emitter (28) is coupled directly or indirectly to the output terminal of the first oscillator (24). 3./ The equipment according to claim 2 characterised in that the first oscillator (24) is coupled to the output 20 terminal of the signal shaping circuit (20) with a first switch (22) inserted. 4. / The equipment according to any of claims 1 - 3 characterised " in that the first counter (30) has an overflow output terminal and an overflow indicator (38) connected to it. 5./ The equipment according to any of claims 1 - 4 characterised in that it has an OR logic function circuit (52), an AND logic function circuit (54) with its first input terminal coupled to the output terminal of the OR logic function circuit (52), a second counter (60) with its input terminal coupled to the output terminal of the AND logic function circuit (54), where the input terminals of the OR logic function circuit (52) are coupled to the output terminals, conveniently to the non-privileged output terminals of the first counter (30) , and the second input terminal of the AND logic function circuit (54) is coupled to the output terminal of the signal shaping circuit (20) . 6./ The equipment according to claim 5 characterised in that the signal generating amplifying unit (10) has a second output terminal, and this second output terminal is coupled to the input terminal of the second counter (60). 7./ The equipment according to claim 5 or 6 characterised in that a second oscillator (70), preferably tuned to a frequency other than the frequency of the first oscillator (24) is coupled to the output terminal of the second counter (60), and the output terminal of the 21 second oscillator (70) is coupled to the input terminal of the sound emitter (28), and the output terminal of the second counter (60) is coupled to the count disabling input terminal . 8. The equipment according to claim 7 characterised in that the output terminal of the first oscillator (24) and the output terminal of the second oscillator (70) are coupled to the input terminals of a summing circuit (26) , and the output terminal of the summing circuit (26) is coupled to the input terminal of the sound emitter (28). 9./ The equipment according to any of claims 5 - 8 characterised in that it has a timing generator (66), and the output of this timing generator (66) is coupled to the resetting input of the second counter (60) . 10./ The equipment according to claim 9 characterised in that the timing generator (66) has timer component ( s ) , preferably timer capacitors (64, 65) that can be inserted or shorted out by a time-span selecting switch (62) . 11./ The equipment according to any of claims 7 - 10 characterised in that the overflow output terminal of the first counter (30) is coupled to the input terminal of the second oscillator (70) . 12./ The equipment according to any of claims 7 - 11 characterised in that the output terminal of the timing generator (66) is coupled to the resetting input terminal of 22 the second counter (60) with a controlled switch (56) inserted, and the controlling input of the controlled switch (56) is coupled to the overflow output terminal of the first counter (30) . 13./ The equipment according to any of claims 5 - 12 characterised in that it has a manual switch (58), preferably a push-button switch, which is coupled between the timing generator (66) and/or the zero-setting input of the second counter (60) and a terminal of appropriate potential. 14. / The equipment according to any of claims 1 - 13 characterised in that the signal generating amplifying unit (10) has an input differential amplifier (11) coupled to the sensing input terminals (1, 2, 3) with its input terminals, a level adjusting amplifier (14) coupled to the output terminal of the input differential amplifier (11) through an amplifier (12) and an separating capacitor (13) , a double signal shaping circuit (18) coupled to the output terminal of the level adjusting amplifier (14) through a filter (15), conveniently an active filter, preferably an narrow band filter, a level amplifier (16) and a capacitor (17), where the output terminals of the double signal shaping circuit (18) constitute the outputs of the signal generating amplifying unit (10) .

Inventors: FEJES LASZLO, GYOERFI ISTVAN, FEJES, LASZLO, GYOERFI, ISTVAN
Applicants: FEJES LASZLO, GYOERFI ISTVAN, FEJES, LASZLO, GYOERFI, ISTVAN
Application year: 1999
Main classification: A61B5
IPC codes: A61B5