GB2101335A

GB2101335A - Electrocardiogram analysers

Info

Publication number: GB2101335A
Application number: GB08217782A
Authority: GB
Inventors: Franc Jager; Marjan Vezjak; Ludvik Gyergyek; Krunoslav Turkulin; Iztok Gabrovec; Damjan Zazula; Franci Solina
Original assignee: Gorenje Tovarna Gospodinjske Opreme N Sol O Velenje; GORENJE TOVARNA GOSPODINJSKE
Current assignee: Gorenje Tovarna Gospodinjske Opreme N Sol O Velenje; GORENJE TOVARNA GOSPODINJSKE
Priority date: 1981-06-18
Filing date: 1982-06-18
Publication date: 1983-01-12
Also published as: FR2508202A1; NL8202433A; ATA234282A; DE3222926A1; YU153781A; GB2101335B; JPS581435A

Abstract

An analyser for analysing electrocardiograms is designed to be driven directly by a standard recording device such as an electrocardiograph. The analyser comprises a multiplexer circuit (6), an output interface (7), a demultiplexer (8), a low-pass filter (1), circuits (2, 3 and 4) operative to eliminate mains interference, a high- pass filter (5), an analog-to-digital converter (9), a random access memory (10), a memory module (11), a microprocessor (12), a programmed clock (17), a keyboard (14), a display means (15) and printing means (16). Details of a patient, including measured blood pressure values, may be entered via the keyboard before a stress test in which heart rate is calculated over suitable interval and extra systoles are detected, and after which an analysis is printed out. <IMAGE>

Description

SPECIFICATION Electrocardiogram analysers This invention relates to electrocardiogram analysers, i.e. apparatus for automatic analysis of electrocardiograms, operating for example on the basis of a protocol prescribed for an exercise test.

As is known, different conditions of the heart muscles can be recorded on paper, in the form of characteristic curves, with the aid of an electrocardiograph. There is a defined correlation between diseased states of the heart muscles and the form of the curves so that cardiologists can recognise different diseased states by analysing the curves, i.e. by evaluating the parameters.

Analysis of recorded electrocardiograms is usually performed visually and is a rather monotonous and time-consuming operation, having a routine character. Therefore, the results are often highly dependent upon the disposition and the individual observations of the physician.

They also depend upon his knowledge and experience.

By virtue of the development of suitable computers, automatic analysis of electrocardiograms has become possible. To date, two kinds of device have been developed for such analyses. The first kind of device includes large computer systems storing enormous quantities of data, i.e. cardiograph records. These systems operate indirectly, i.e. electrocardiograms are first recorded, e.g. on a magnetic tape, and the tape is subsequently transported to a data-processing computer. The second kind of device includes small transportable devices which analyse electrocardiograms directly, i.e. while the patient is connected to the electrocardiograph. Some of these devices employ wired logic. Recently, however, such devices have been developed where the operation of the device is based on the use of a microprocessor system as a controlling and supervising unit.

The above-mentioned known devices avoid thf above-mentioned imperfections of visual analysis of recorded electrocardiograms and consequently provide an objective analysis of the diseased state. However, they are on the other hand subject to the disadvantage that they are basicallss designed to function with discrete items of cardiological equipment, which undoubtedly reduces the applicability thereof.

According to the present invention there is provided an electrocardiogram analyser capable of analysing information from a standard recording device, the analyser comprising: a multiplexer circuit having inputs to which, in use, the recording device is connected; an output interface having an output connected to an input of the multiplexer circuit; a demultiplexer having an input connected to the output of the output interface, a low-pass filter having an input connected to an output of the multiplexer circuit; first, second and third circuits for the elimination of mains interference, the first and third circuits having inputs connected to an output of the low-pass filter, an output of the first circuit being connected to an input of the second circuit, and an output of the second circuit being connected to another input of the third circuit;; a high-pass filter having an input connected to an output of said third circuit; an analog-to-digital converter having an input connected to an output of the high-pass filter; a peripheral adapter connected to an output of the analog-to-digital converter, the output of the converter being connected also to an input of the output interface, a random access memory, memory module, microprocessor and programmed clock all connected to the peripheral adapter, and an alphanumeric keyboard, display and printer also all connected to the peripheral adapter.

An embodiment of the invention described hereinbelow comprises an electrocardiogram analyser fully able to work from outputs of existing standard electrocardiographs so that it is thereby possible to modernise existing corresponding equipment. The analyser operates in accordance with a protocol for an excercise test, i.e. for a situation where the patient is physically loaded or stressed and the operation of his heart is observed in this state.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, wherein: Figure 1 is a block-diagram of an electrocardiogram analyser embodying the invention; Figure 2 shows a typical form of electrocardiogram with the most important parameters necessary for analysis; Figure 3 is a circuit diagram of a self-adapting or self-adjusting filter employed in the analyser for eliminating mains frequency interference; and Figure 4 is a circuit diagram of a pulse circuit connecting function buttons of the analyser to a microprocessor and peripheral adapter thereof.

Figure 1 shows a microprocessor-based electrocardiogram analyser comprising a low pass filter 1, circuits 2, 3, 4 for the elimination of mains interference, a high-pass filter 5, (the circuits 1 to 5 all being analog active filters), a multiplexer circuit 6, an output interface 7, a multiplexer 8, a 10-bit analog-to-digital (A/D) converter 9, a random access memory (RAM) 10, a memory module 11, an 8-bit microprocessor 12, an adapter 13, an alphanumeric keyboard 14, a numerical display 15, a printer 16 and a programmed clock 17. As shown by arrows in Figure 1 , the multiplexer circuit 6 has inputs for connection to any standard recording device, for instance an electrocardiograph, in which case the so-called SCOPE-outputs of the electro cardiograph may be used.An output of the interface 7 is connected to an input of the multplexer 6 and is at the same time connected to an input of the multiplexer 8. An output of the multiplexer 6 is connected to an input of the low pass filter 1. An output of the filter 1 is connected to inputs of both the circuits 2 and 4. An output of the circuit 2 is connected to an input of the circuit 3, an output of which is connected to a second input of the circuit 4. An output of the circuit 4 is connected to an input of the high-pass filter 5, an output of which is connected to an input of the 10-bit A/D converter 9.An output of the A/D converter 9 is connected to an input of the output interface 7 and also to the peripheral adapter 13, which is connected to the RAM 10, the memory module 1 the 8-bit microprocessor 12, (which is for example an NC6800), and to the programmed clock 17. The peripheral adapter 13 is also connected to the alphanumeric keyboard 14, to the display 15, which displays time and heart pulsation data, and the printer 16.

Figure 3 shows in detail a high-quality selfadapting or self-adjusting filter for the elimination of main interference. In this filter, the anode of a diode D20 is connected to a separate winding of a mains transformer and its cathode is connected via a resistor H20 to the base of an NPN transistor T The emitter of the transistor T20 is connected to earth and the collector is connected (via a resistor R21) to a supply voltage +VDD and also to an input of a voltage controlled oscillator (VCO) 21.An output of the VCO 21 is connected to an input of a binary counter 22, outputs 120, 121, 122 and 122 of which are connected to control inputs of analog switches 23, 24. Outputs of the switches 23, 24 are connected to ends of respective capacitors C230-C246, the other ends of which are connected together and coupled to one end of a variable resistor P20 and to an input of a separating or isolating stage 25, an output of which is connected to an input of a low-pass filter 30. An output of the low-pass filter 30 is connected to an input of a high-pass filter 31.An output of the filter 31 is coupled to an input of an adder 40 via a variable resistor P32, the same input also being connected to the other end of the variable resistor P via a resistor R40 and to a connector for an 20 input signal on an input V21. An output of the adder 40 is connected to the input of the A/D converter 9.

Figure 4 represents a pulse circuit for connecting function buttons on the keyboard 14 to the microprocessor 12 and the peripheral adapter 13. The pulse circuit comprises diodes D40, D141 and D142 and resistors R,40, R141 and R,42. The junctions of each diode and resistor, marked V,40, V141 and V,42, respectively, comprise inputs that lead to three function buttons designated ANALYSIS, INTERRUPTION and STOP, which can connect said inputs to ground.

The anodes of the diodes D,40, D141 and D,42 are connected together and connected via a resistor R143 to the base of a PNP transistor T,40. A capacitor C140 is connected between the base and the emitter of the transistor T,40. The collector of the transistor T,40 is connected to a synchronisation or clock input C, of a first D-type bistable multivibrator in an integrated circuit It140.

A resistor R145 is connected between an input R, and an output Q1 of the first D-type multivibrator.

Additionally, the input R, is connected to earth via a capacitor C,4,. Likewise, a resistor R146 is connected between an input R2 and an output Q2 of a second D-type multivibrator in the integrated circuit It,40. A diode D142 is connected in parallel with the resistor R,4,. The input R2 is connected to earth via a capacitor C,42. An output 1,40 of the multivibrator integrated circuit IC,40 is connected to the microprocessor 12.

The operation of the microprocessor electrocardiogram analyser will now be described.

The microprocessor 12 (e.g. of NC6800 type) executes program instructions stored in the memory module 11 (e.g. of TMM323 type). The memory module 11 contains a program having an operational part prescribing the operation of the whole system and an analytical part prescribing analytical algorithms for the definition of cardiographic parameters.

On commencing operation of the device, a request for entry of the date and time is given over the printer 16. The operator enters a reply by means of the alphanumeric keyboard 14. The system receives the reply over the peripheral adapter 13 (e.g. of NC6821 type) and starts the programmed clock 17 (e.g. of NC6840 type), which henceforth states the exact time of day of the operation until the system is switched off by interrupting the line to the microprocessor 12.

By virtue of connection of a standard electrocardiograph to the multiplexer circuit 6, amplified bioelectrical signals from the electrocardiograph enter the multiplexer circuit. By means of the keyboard 14 activating the system according to the program by a call to the peripheral adapter 13, there can be recorded onto the output interface 7 a code representing a channel which is to be analysed. At the same time, this code is transferred to the demultiplexer 8 whereby an LED indicator corresponding to the chosen channel is caused to glow.

Prior to the test itself it is possible to insert all data on the patient by means of the keyboard 14.

All data are printed out by the printer 16, the data being: an indication whether the patient's testing is performed with the aid of an ergometer or over a treadmill; family name and given name of patient; age, sex, weight and data on physical activities of patient; patient number; name of doctor in charge of treatment; and transfer diagnosis.

Prior to the test or immediately thereafter a special function can be activated via the keyboard 14 on request, which according to the program transfers data entered via the keyboard 14 to the printer 16. In this way it is possible to supplement the standard protocol by individual observations and comments.

Every electrocardiograph contains a reference source with a voltage or signal of 1 mV being used for calibration. Prior to the beginning of the test this signal reaches the analyser in the form of a train of rectangular pulses. On special request over the keyboard 14, a calibration algorithm is stored which forms a numerical equivalent of 1 mV on the basis of input analog pulses. The analog signal passed from the multiplexer circuit 6 over the series of analog active filters 1, 2, 3, 4, and 5 to the 10-bit AID converter 9. The AID converter 9 samples the input signal at a predetermined frequency, the converter being controlled by the programmed clock 17. The individual samples are stored in series at a predetermined location in the RAM 10, which is for example of TMM3 14 type.By means of the program, positive and negative jumps or transitions of the input signal are recognised so that eleven samples are stored between each jump and the next jump. Equally positioned samples of eight subsequent calibration pulses are added to these samples, the average difference between the levels before and after the positive and the negative transitions, respectively, of the signal being the numerical equivalent of the calibration signal, i.e. 1 mV. The received number is stored in the RAM 10.

Programs executed by the analyser encompass two methods of starting: according to one the time measurement representing the test duration is not switched in as yet, and according to the other the time measurement is switched in. All other starting steps are the same. The selected ECG (electrocardiograph) signal, which corresponds in form to the left precardial leads shown in Figure 2, has to pass through the multiplexer circuit 6. In an exercise test, such a signal is accompanied by several kinds of interference: due to bad contact of electrodes with the surface of the skin of the patient, and due to muscle potentials, interference arises whose frequency spectrum is generally higher than the frequency contents of the ECG signal; due to breathing and movement of the thorax a low-frequency drift of the isoelectric line (i.e.

the signal zero or base line) is superposed on the basic signal; the mains frequency (typically 50Hz) which lies in the frequency spectrum range of the ECG signal.

All of these interference components have to be eliminated, for which reason the abovementioned analog active filters 1 to 5 are used.

The operation of these filters is as follows. The low-pass filter 1 eliminates the high frequency interference and the high-pass filter 5 eliminates the low-frequency interference. The combination of the circuits 2, 3, 4 provides for the elimination of the mains interference. It is important that the mains frequency is suppressed as much as possible, whereas frequencies in the neighbourhood of the mains frequency must not be affected excessively. As the mains frequency is not perfectly constant, the required effect might not always be achieved with a high-quality suppression filter. A solution is presented by a transversal filter which guarantees a high quality and at the same time its centre frequency can be varied by means of an external pulse generator without any way changing its transmission characteristic.

The filter shown in Figure 3 is intended for elimination of the mains interference and it operates as will now be described. A control signal generated by the separate winding on the mains transformer and having the sinusoidal form of the mains frequency passes via the input V20 to the NPN transistor T20 which forms therefrom a train of rectangular pulses. The rectangular pulses synchrnnise the VCO 21, the idling frequency of which is set to approximately N times the value of the mains frequency where 2N is the number of states in the binary counter 2. The counter 22 is arranged as a frequency divider connected to the feedback loop for the VCO 21, whereby the VCO oscillates exactly N times faster than the mains frequency.The outputs 120, 121, 122 and 123 of the counter 22 are connected to the control inputs of the analog switches 23, 24 which switch N capacitors separately one after another to earth in synchronism with the VCO 21.

The input signal passing via the input V21 to the variable resistor P20 enters the above-described transversal filter, which passes the timing frequency only, i.e. the mains frequency and its harmonic frequencies. The separating stage 25 leads the separated signal components to the low-pass filter 30, which eliminates higher harmonic frequencies, and to the high-pass filter 31 which compensates for the transmittance of the transversal filter at very low frequencies. Only those mains frequency interference components which are phase shifted by 1 800 reach the adder 40. By means of the variable resistor P32 it is possible to regulate the signal amplitude so that complete compensation can be obtained for interference supplied together with the useful signal by the direct line over the resistor R40.In this way, mains frequency components in the output signal are attenuated by approximately 40 dB. The quality of the suppression filter as just described is dependent upon the value of the variable resistor P20, upon the value and number of switched capacitors C230-C248 and upon the centre frequency coO i.e. the oscillator frequency Q is given by:

where C is the value of the switched capacitors in F, N is their number and P20 is the set value of the variable resistor in ohms.

The filtered signal reaches the input of the AID converter 9 (e.g. of AD574JK type) which converts the signal into a series of digits.

The sampling ensues at a frequency defined by a program, e.g. 500 Hz, dictated by the programmed clock 17. The samples are transferred to and stored in the RAM 10. At the same time, by means of the program, a search is carried out for single QRS complexes (systoles in the input signal). As soon as a QRS complex is found, it is evaluated and classified according to mathematical methods as a normal systole or an extrasystole. Extrasystoles are further divided into supraventricular and ventricular systoles, the numbers of both kinds being accumulated at special positions in the RAM 10 throughout the test. An average systole is formed of normal systoles, represented with a sequence of 256 samples, and is stored in the RAM 10.

Each detection of a QRS complex actuates a program conversion of the heart pulse frequency.

The calculated value is transferred to the display 15, which is conveniently a 7-segment light digital display 15, via the peripheral adapter 13.

On another digital display there is displayed throughout the test the time (in minutes and seconds) during which the patient has been subjected to stress or loading. The time conditions are regulated by the programmed clock 17, which activates the microprocessor 12 by the program stored in the memory module 1 1 with the aid of an interrupt line. The display 15 is controlled by the microprocessor 12 via the peripheral adapter 13.

The moment when loading of the patient is started, it is necessary to press a START button on the keyboard 14. By means of a determined code, this starts the clock 17, the consequence thereof being the above-described process of sampling, detecting, averaging and displaying. In addition to the START button and the alphanumeric buttons, which all generate corresponding hexadecimal codes, uncoded buttons also are positioned on the keyboard 14.

Through these buttons, requests for an analysis of the input data (ANALYSIS), for an interruption of the loading of patient (INTERRUPTION), and for a complete stop at test (STOP) can be given. On pressing these buttons the unmasked interrupt line of the processor 12 is activated, i.e. the operation of the processor 12 is thereby stopped irrespective of the activity currently being executed. Such absolute interruption must not continue for a long time as in this case all functions of the analyser would cease.

The circuit shown in Figure 4 provides that, on pressing the three buttons mentioned above, a pulse of a duration of only approximately 3 microseconds is generated, even though the button has been pressed for a much longer period of time or has been pressed several times in sequence. In the circuit of Figure 4, a PNP transistor T,40 is responsive to the pressing of any of the function buttons, due to the diodes D,40, D141 and D142 and the resistors R,40, R141 and R142 acting as an OR-circuit, to generate a positive voltage jump or transition and operate as an inverter. The capacitor C140 filters out random interference and voltage peaks generated by contact chatter when the button is pressed.On switching over the transistor T,40, the voltage jump or transition is transferred to the clock input C of the first D-type bistable multivibrator of the integrated circuit It140, whereupon a high voltage level is generated on the output Q, and a low voltage level is generated on the output Q,. After a time defined by the components R145 and C141, a reset pulse is supplied to the multivibrator input R,, whereupon the output Q, changes over to a low voltage level and the output Q1 changes over to a high voltage level. This last change actuates switching over of the second D-type multivibrator in the integrated circuit IC140.Consequently, a low voltage level is established on the output Q2, which, being connected to the input D1, makes switching over of the state to Q1 or respectively, impossible. This blocking lasts until, after a time defined by the components R148 and C142, the second multivibrator is reset over the input R2. The diode D,43 assists in possibly prompt discharging of the capacitor C142 so that the circuit is ready for a new cycle of operation.

The inputs V140 V141 and V142 are also connected to the peripheral adapter 13 to inform the microprocessor 12 of the identity of the button that generated the interrupt. As already described, the interrupt pulse is generated on the output Q, of the first D-type multivibrator and is transferred directly to the unmasked interrupt line at the microprocessor 12 via the line connected to the output 1140.

When a request for an analysis is made by pressing the ANALYSIS button the program enters a special indicator bit into the random access memory 10. When the next requested average of M heart pulses is formed (where M is high enough so that a statistically satisfactory average can be obtained, but not however so large that the average is not formed for an excessively long time, a good choice being M=2m, e.g. M=1 6) setting of the indicator bit causes execution of programs for an analysis operation involving a mathematical definition of characteristic parameters in the ECG input signals.The remaining analyser functions described above are not thereby interrupted because they are regulated by the clock 17 which interrupts the operation of the processor 12 at regular time intervals and commands the processor to execute the sampling, to take input data from the keyboard 14, to transfer data to the printer 1 6 or the digital displays, etc. The analyser, consequently, operates on a time sharing principle which is provided for by a corresponding operational part of the program recorded in the memory module 11.

I ne average ot the systoles treated by the analysing program must not be accessible for the introduction of new samples while the analysis is being carried out. For this reason, two like or equal data interfaces are positioned in the RAM 10 and the M systole average is entered alternatively therein. The results of the analysis are stored in a BCD code as a vector in the RAM 10. An output program combines the same with accompanying text recorded in the memory module 11, printing them according to the protocol by means of the printer 1 6.

If the patient become tired or if an abnormal reaction (a too high pulse or blood pressure) arises, the loading on the patient has immediately to be removed. The test is thus to be interrupted, which information is given to the analyser by the operator pressing the INTERRUPTION button. At this moment, the indication value showing the test duration time is set to zero (time measurement after the test) and, automatically, a request for an analysis is generated, the results of which are written out, after which the printer 16 prints out reports as to the minute and second at which the test was interrupted. It is necessary to type in, via the keyboard 14, the reason for the interruption, which is also printed by the printer 16. While the patient rest or calms down, all functions of the analyser become available.

Consequently, it is at any time again possible to analyse the input ECG signal.

By pressing the STOP button the analyser ceases to follow the input signal, i.e. the programmed clock 17, having given the sampling command, stops. The printer 16 prints out the total number of extrasystoles during the whole test, i.e. of the supraventricular and ventricular kind, the maximum allowable heart pulse frequency with regard to the age and sex of the patient, and the maximum pulse in fact attained during the test. The analyser may be so designed that the maximum blood pressure attained during the test may be entered via the keyboard 14. If this is carried out automatically, the product of this pressure and the maximum pulse attained is calculated, this product being divided by 1000 and simultaneously also printed out. The final printed outputs include data on the theoretical standard for consumption of oxygen on loading with regard to the age, sex, weight and the physical activities of the patient. The consumption of oxygen in fact attained can again be entered via the keyboard 14 or left for the analyser to define the same from the duration of test.

The printer 16 may draw minute hystograms for the course of the heart frequency, the ratio between an exercise wave R (Figure 2) versus a pre-exercise wave P, for depression of the J-point, the slope of a segment ST and for the integral below the segment ST. Thereafter, automatic initialisation of the analysis follows so that it is ready for connection to a new patient.

Claims

1. An electrocardiogram analyser capable of analysing information from a standard recording device, the analyer comprising: a multiplexer circuit having inputs to which, in use, the recording device is connected; an output interface having an output connected to an input of the multiplexer circuit; a demultiplexer having an input connected to the output of the output interface, a low-pass filter having an input connected to an output of the multiplexer circuit; first, second and third circuits for the elimination of mains interference, the first and third circuits having inputs connected to an output of the low-pass filter, an output of the first circuit being connected to an input of the second circuit, and an output of the second circuit being connected to another input of the third circuit; a high-pass filter having an input connected to an output of said third circuit;; an analog-to-digital converter having an input connected to an output of the high-pass filter; a peripheral adapter connected to an output of the analog-to-digital converter, the output of the converter being connected also to an input of the output interface, a random access memory, memory module, microprocessor and programmed clock all connected to the peripheral adapter, and an alphanumeric keyboard, display and printer also all connected to the peripheral adapter.

2. An analyser according to claim 1, wherein the anode of a diode is connected to a winding of a mains transformer via an input, the cathode of the diode is connected via a resistor to the base of an NPN transistor, the emitter of the transistor is connected to earth, the collector of the transistor is connected via a resistor to a supply voltage and to an input of a voltage controlled oscillator, an output of the oscillator is connected to an input of a binary counter, outputs of the counter are connected to control inputs of analog switches, outputs of the switches are connected to a plurality of capacitors, the ends of the capacitors not connected to the switch outputs are connected together and coupled to one end of a first variable resistor and an input of a separating stage, an output of the separating stage is connected to an input of a low-pass filter, an output of the lowpass filter is connected to an input of a high-pass filter, an output of the high-pass filter is connected to an input of an adder via a second variable resistor, said input of the adder is connected via a resistor to the other end of the first variable resistor and is connected to receive an input signal, and an output of the adder is connected to the input of the analog-to-digital converter.

3. An analyser according to claim 1 or claim 2, wherein the keyboard is connected to the microprocessor and the peripheral adapter by a pulse circuit comprising interconnected diodes and resistors, the junctions of the individual diodes and the resistors form inputs connected to contacts of three function buttons, other contacts of which are connected to ground, the anodes of the diodes are connected together and are connected via a resistor to the base of a PNP transistor, the emitter of the transistor is connected to a supply terminal and to one pole of a capacitor, the other pole of the capacitor is connected to the base of the transistor, the collector of the transistor is connected to earth via a resistor and is connected to a clock (C) input of a first D-type bistable multivibrator in an integrated circuit, a resistor is connected between the R input and the Q output of the first multivibrator, one pole of a capacitor is connected to the R input of the first multivibrator, the other pole of the capacitor is connected to earth, the Q output of the first bistable multivibrator is connected to the clock (C) input of a second bistable multivibrator in the same integrated circuit, the Q output of the second multivibrator is connected to the data (D) input of the first multivibrator, the Q output of the second multivibrator is connected to the R input of the second multivibrator via a resistor having a diode connected in parallel therewith, the R input of the second multivibrator is connected to earth via a capacitor, and an output of the pulse circuit is connected to the microprocessor and to the junction of the output Q of the first multivibrator and the clock (C) input of the second multivibrator.

4. An analyser according to claim 1, claim 2 or claim 3, wherein the analog-to-digital converter is a 1 0-bit analog-to-digital converter.

5. An analyser according to any one of the preceding claims, wherein the microprocessor is an 8-bit microprocessor.

6. An electrocardiogram analyser substantially as herein described with reference to the accompanying drawings.