Artifact Detecting Apparatus in the Measurement of a Biological Signal

FIG. 1 is a diagram showing an electrocardiogram waveform,

FIG. 2 is a diagram showing an electrocardiogram waveform accompanying a high frequency artifact,

FIG. 3 is a diagram for explaining the principle of artifact detection according to the artifact detecting apparatus of the present invention,

FIG. 4 is a block diagram showing one embodiment of the present invention, and,

FIG. 5 is a diagram showing the signal waveform of each point in the apparatus shown in FIG. 4.

One embodiment of the artifact detecting apparatus according to the present invention is shown in FIG. 4, and the signal waveform of each point in the apparatus shown in FIG. 4 is shown in FIG. 5.

In FIG. 4, 1 is a high-pass filter. This high-pass filter 1 is provided for extracting only high frequency components from an electrocardiogram signal. 3 is a comparing and pulse-generating circuit. This comparing and pulse-generating circuit 3 is a circuit for converting into pulses an R wave of the normal electrocardiogram, an R wave distorted by the abnormal electrocardiogram due to ventricular extrasystole, and the like, and the high frequency artifact having the amplitude and frequency components approximately equal to an R wave of the normal electrocardiogram. That is to say, the comparing and pulse-generating circuit 3 is a circuit which compares the output signal S(1) voltage from the high-pass filter 1 with the output signal S(2) (threshold voltage E.sub.0) from the threshold voltage setting circuit 2 and generates a pulse or pulses when the output signal S(1) voltage exceeds the threshold voltage E.sub.0. The comparing and pulse-generating circuit 3 may be a Schmitt circuit as a concrete circuit.

Threshold voltage E.sub.0 set in the threshold voltage setting circuit 2 is set to a voltage value capable of detecting at least one voltage level of a plurality of voltage levels corresponding to the points Q, R, and S, respectively, having high frequency components among the section points existing in the electrocardiogram, a voltage value capable of detecting the high frequency artifact having an amplitude voltage value which does not have an influence on the extraction of the section points necessary to the recognition of the abnormal electrocardiogram waveform, and a maximum value of the amplitude voltage under the consideration that a T wave of the electrocardiogram signal has passed the filter and may have a relatively great amplitude.

Integrating circuit 5 is a circuit for integrating the high frequency pulses obtained through the comparing and pulse-generating circuit 3. Clock circuit 4 generates a pulse S(4) at a predetermined time interval t.sub.0 and resets the integrated output of the integrating circuit 5. 6 is a detecting level voltage setting circuit. The detecting level voltage E.sub.1 is set in this detecting level voltage setting circuit 6. This detecting level voltage E.sub.1 is set to a value lying between the integrated output voltage corresponding to the fifth pulse of the pulses input to the integrating circuit 5 and the integrated output voltage corresponding to the sixth pulse, for example, when the predetermined time interval t.sub.0 of the pulse as shown in FIG. 5, (4) is 100 (msec). 7 is a comparing and detecting circuit. This circuit is a circuit for comparing the output signal S(5) voltage of the integrating circuit 5 with the output signal S(6) (detecting level voltage E.sub.1) of the detecting level voltage setting circuit 6 and generating a pulse as an artifact detection signal S(7) at the output terminal OUT when the output signal S(5) voltage exceeds the detecting level voltage E.sub.1.

This artifact detection signal S(7) can be used in the desired application and supplied to, for example, an elimination circuit for eliminating the high frequency artifact in an automatic electrocardiogram analyzer or a recognition stopping apparatus for the prevention of misrecognition in an arrhythmia recognition apparatus. For example, in the case of the elimination circuit of the high frequency artifact, the waveform portions at which the high frequency artifact occurs in the electrocardiogram waveform can be automatically eliminated and an electrocardiogram waveform free of the high frequency artifact can be obtained, based on the artifact detection signal from the comparing and detecting circuit 7.

The mode of operation of the artifact detecting apparatus constructed as mentioned above will be explained hereinafter. The electrocardiogram signal S(c) applied to the input terminal IN as shown in FIG. 5, (1) is input to the high-pass filter 1, where the low frequency components are removed, and the electrocardiogram signal S(1) as shown in FIG. 5, (2) is obtained. This electrocardiogram signal S(1) is input to the comparing and, pulse-generating circuit 3 and compared with the threshold voltage E.sub.0 from the threshold voltage setting circuit 2, where only the electrocardiogram signal having exceeded the threshold voltage E.sub.0 is converted into the high frequency pulses S(3) having a single amplitude and a single pulse width as shown in FIG. 5, (3). The high frequency pulses obtained in the comparing and pulse-generating circuit 3 are input to the integrating circuit 5 and integrated. Then, the integrating circuit 5 is reset by the output pulse S(4) of the clock circuit 4 as shown in FIG. 5, (4), so that the waveform as shown in FIG. 5, (5) is obtained as the output signal S(5) of the integrating circuit 5. The output signal S(5) of the integrating circuit 5 is input to the comparing and detecting circuit 7 and compared with the preset detecting level voltage E.sub.1. Based on this comparison, the artifact detection signal S(7) as shown in FIG. 5, (6) is obtained at the output terminal OUT as the output of the comparing and detecting circuit 7 when the output signal S(5) voltage of the integrating circuit 5 exceeds the detecting level voltage E.sub.1. This artifact detection signal S(7) can be used in the desired application as aforementioned.

On the other hand, the electrocardiogram from the human organism is detected by means of at least the normal twelve leads. The normal twelve leads have a different waveform for each lead and include a lead having a positive R wave and a lead having a negative R wave. The phenomenon wherein the waveform differs for each lead occurs in the abnormal electrocardiogram waveform as well, and includes a lead having a positive R wave and a lead having a negative R wave. Therefore, the threshold voltage E.sub.0 can be set as negative or as both positive and negative under the consideration of a lead having a negative R wave, although in the abovementioned embodiment only the case wherein the threshold voltage E.sub.0 input to the comparing and pulse-generating circuit is positive is described. Such a change of the threshold voltage can be readily carried out by changing the value of each constituent element.

To the contrary, where the threshold voltage is set at only positive, the waveform obtained by converting a negative electrocardiogram waveform in the input signal to positive, a so-called absolute value waveform, may be generated by means of an inverter when the electrocardiogram signal is input to the comparing and pulse-generating circuit. This absolute value waveform is generally used in the electrocardiogram analyzer and is well known.

Also, in the cases that the above-mentioned absolute value waveform is input, that the Q wave and S wave of the normal electrocardiogram have the possibility of being simultaneously detected as the high frequency pulse, that there is a lead in which the Q wave and S wave have a relatively great amplitude, and the like, there is a possibility that the number of the high frequency pulses in the normal electrocardiogram waveform and abnormal electrocardiogram waveform will exceed the threshold "6" of the number of the aforementioned high frequency pulses. Therefore, in order to prevent this, both the setting of the threshold voltage E.sub.0 input to the comparing and pulse-generating circuit and the change of the setting of the detecting level voltage E.sub.1 input to the comparing and detecting circuit are changed.

Furthermore, in the above-mentioned embodiment the integrating circuit is used as the means for counting pulses output from the comparing and pulse-generating circuit. However, the means is not restricted to the integrating circuit and may be a counting circuit such as a binary counter which performs a comparison according to the sequence number.

Moreover, in the above-mentioned embodiment the threshold voltage E.sub.0 is set so that the high frequency amplitude voltage of Q, R and S wave can be detected, the predetermined time interval t.sub.0 is set to contain the high frequency components of the Q, R, and S waves, and the detecting level voltage E.sub.1 is set to a detecting level under the consideration of the high frequency components of arrhythmia. However, the values of the threshold voltage E.sub.0, the predetermined time interval t.sub.0, and the detecting level voltage E.sub.1 are not restricted to the above-mentioned. For example, the precision of discrimination of the high frequency artifact can be improved by setting the threshold voltage E.sub.0 so that only the high frequency amplitude voltage of the R wave can be detected, by setting the predetermined time interval t.sub.0 to a shorter interval, and by setting the detecting level voltage E.sub.1 to a value under the consideration of only the high frequency components of the R wave. Accordingly, the detection of the high frequency artifact can be carried out by appropriately selecting the respective value independently of or dependently on each other according to the purpose of diagnosis.