JPH024645Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a respiratory monitor that measures and monitors a patient's respiratory movement based on changes in thoracic impedance.

[Conventional technology]

In the field of medical electronics, there is a constant need to accurately measure human respiratory rate.

Respiratory monitors of the type described above monitor the patient's breathing frequency, record the breathing curve, and indicate when abnormal breathing conditions, such as apnea, are detected. The impedance changes caused in the chest by respiratory movements are obscured primarily by the interference of the heartbeat. This interference is commonly referred to as a cardiovascular artifact.
Hereinafter, this will be abbreviated as "heartbeat murmur."
Thoracic impedance changes periodically due to both respiratory and cardiac movements. However, the amplitude of changes due to heartbeats is much smaller than the amplitude of changes due to respiratory motion, and the frequency of heartbeats is generally higher than the frequency of breathing.

In order to suppress such disturbances caused by heartbeats, conventional respiratory monitors input electrical signals obtained from changes in thoracic impedance to a trigger circuit, and this trigger circuit is used to set the amplitude of the input signal to a predetermined threshold. ) value was exceeded, an output signal was generated only when the value was exceeded. This threshold was selected by manual adjustment to be lower than the amplitude of the signal generated by respiratory movements and higher than the amplitude of the signal generated by heartbeats. One drawback of this traditional respiratory monitor is that the amplitude of the respiratory signal not only varies from patient to patient, but also changes over time for the same patient, requiring frequent readjustment of the threshold. It is a must. Also, other drawbacks are
The period of impedance change due to respiratory motion is generally larger than the period of impedance change due to heartbeat, and since the two periods are different, the threshold value cannot be adjusted accurately.

To avoid such manual readjustment of trigger thresholds, other prior art respiratory monitors have included trigger level controls. This control sets the trigger level to some fraction of the actual amplitude of the breathing signal, for example 2/3.
It automatically adjusts to The readjustment was performed with some delay mainly in response to large-amplitude respiratory signals, and was made to be unaffected by interference signals occurring between these large-amplitude signals.

Further, in this breathing monitor, a lower limit was set for the threshold value, which was larger than the minimum amplitude of the breathing signal, but this lower limit had to be larger than the maximum possible amplitude of the heartbeat signal. In reality, these two requirements cannot be met simultaneously, since the amplitude of the breathing signal may be equal to or smaller than the amplitude of the heartbeat signal. That is, if the lower threshold is set so high that it is always greater than the amplitude of the heartbeat signal, the respiratory monitor may not respond to weak respiratory signals. Also, if the lower threshold is set low enough to respond to weak respiratory signals, automatic readjustment will not occur when an apnea condition occurs or when the amplitude of the respiratory signal is lower than the amplitude of the heartbeat signal. . This is a result of the threshold being lower than the amplitude of the heartbeat signal. Therefore, the trigger circuit will provide a signal from the heartbeat to the respiratory monitor, erroneously indicating respiratory movements.

[The problem that the idea aims to solve]

The problem of this invention is to reliably detect heartbeat murmurs included in respiratory signals, and to prevent the patient's heartbeat movement by, for example, interrupting the operation of the respiratory monitor when heartbeat murmurs are detected a certain number of times in a row. This is to ensure that it is not mistaken as a breathing exercise.

[Means and actions to solve the problem]

In the present invention, a respiration signal obtained from a respiratory movement measurement device (impedance pneumograph) based on changes in thoracic impedance is supplied to a waveform processing circuit that detects a portion of the signal where the impedance suddenly decreases. Respiratory signals typically include portions where the impedance repeatedly decreases sharply due to cardiovascular motion.

First, the respiratory signal is differentiated and then passed through a filter to detect a negative slope of impedance change that is greater than a predetermined value and emphasizes this to obtain a signal -dz/dt. A heartbeat murmur is an abnormality in the patient's ECG (electrocardiogram) signal.
It appears as a negative slope in the respiratory signal just after the QRS complex. Therefore, after the detection of each QRS complex, a comparator activation pulse with a predetermined duration is generated to activate the comparator, and during the duration of this comparator activation pulse, a −dz/dt signal is generated. , the comparator generates a pulse indicating the presence of a heartbeat murmur.

This pulse is counted as a heartbeat murmur by a counter that is reset when the comparator activation pulse and the -dz/dt signal do not match, and when the heartbeat murmur is detected a predetermined number of times (for example, 4 times) in succession,
It is also possible to prohibit the gate circuit that passes input signals to the respiratory monitor body. Inhibiting (closing) the gate circuit to the respiratory monitor body prevents heartbeat murmurs from being counted as breathing in the respiratory monitor.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

Fig. 1 is a block diagram showing a preferred embodiment of the present invention, Fig. 2 is a waveform diagram showing the operation of Fig. 1, and Fig. 3 is a typical respiratory signal obtained from a respiratory movement measurement device based on changes in thoracic impedance. A waveform diagram showing
FIG. 4 is a waveform diagram showing a typical ECG signal having a QRS complex waveform, and FIG. 5 is a circuit diagram showing an example of a waveform processing circuit used in the present invention.

FIG. 1 shows only the parts of the respiratory monitor that are relevant to the present invention, and other parts of the respiratory monitor are omitted from illustration. The respiratory monitor, which monitors a patient's respiratory movements by measuring changes in their thoracic impedance, is explained in detail in the book "Biophysical Measurements" published by Tektronix, Inc. in 1970. . Furthermore, each block in FIG. 1 is constituted by circuits well known to those skilled in the art, and detailed explanations of these circuit configurations will be omitted. The role of each block with respect to the entire device will be described below.

As shown in FIG. 1, the first input signal to the present invention is a respiratory signal 5 as shown in FIG. What is shown in the circle in the same figure is a heartbeat murmur.
Sometimes it does not appear in such a clear form. This respiratory signal is obtained from an impedance pneumograph. This device typically has a pair of electrodes that are attached to the patient's skin near the thoracic cavity, and a power source connected to the electrodes drives electrical current through the thoracic cavity. Typically, this power source is an alternating current constant current source.

The thoracic electrical impedance detected by the electrodes consists of two impedance components: one with a relatively stable value known as the average thoracic impedance, and the other with a relatively stable value, known as the average thoracic impedance.
One is an impedance component whose value varies, known as respiratory impedance. This respiratory impedance changes with the inhalation and exhalation movements of the lungs, and is therefore used to measure the patient's respiratory movements. Such an impedance neumograph comprises an impedance measuring bridge and a demodulator and amplifier to generate a respiratory signal 5 as shown in FIG.
occurs. This impedance pneumograph is well known to those skilled in the art and will not be further described.

The second input signal to the present invention is a QRS trigger pulse 15 derived from a heartbeat as shown in FIG. 2A. This pulse is connected to the patient.
Although it can be obtained from an ordinary ECG monitor (not shown), it is best to generate it after the completion of the well-known QRS complex. The duration of QRS trigger pulse 15 is
It is approximately 100 milliseconds. A typical ECG waveform including the QRS complex is shown in Figure 4.

In FIG. 3, as mentioned above, the negative distortion superimposed on the breathing signal 5 (shown within the dotted circle).
is caused by heartbeat motion, and the breathing signal 5 consists of two signal components: a signal component indicating only breathing and a heartbeat noise signal component. FIG. 2C is an enlarged view showing only the heartbeat noise signal component of the respiratory signal 5. Heartbeat murmur is characterized by appearing as a negative impedance change after the QRS complex wave. The negative slope or decrease in thoracic impedance due to heartbeat motion is caused by the perfusion of blood through the pulmonary vascular system, initiated by the evacuation of the left ventricle of the heart.

The respiratory signal 5 is first input to the waveform processing circuit 10 . The waveform processing circuit 10 includes, for example, a differentiator 100, a rectifier 105, and a limiter 1 as shown in FIG.
10 and a filter network 115 to detect and enhance negative slopes of the respiratory signal 5 that are greater than a predetermined value and attenuate the remainder of the signal. Heart rate murmurs typically have a slope of -4 or -5 ohms/second. The thus differentiated signal -dz/dt25 is shown in FIG. 2D. This signal 25 is input to a comparator 30. The other input to comparator 30 is comparator activation pulse 35 shown in FIG. 2B. The comparator activation pulse 35 is generated from the QRS trigger pulse 15 described above as follows.

The QRS trigger pulse 15 is first input to a delay circuit 20 having a delay time of 50 milliseconds. This delay is to compensate for the electromechanical delays inherent in cardiac muscle movement. This delay occurs from the time the QRS complex occurs until the impedance reduction due to left ventricular drainage appears in the respiratory signal.
The delayed QRS trigger pulse is input to comparator activation circuit 40. This circuit 40 includes, for example, two
A timer that generates an output pulse with a duration of 15 milliseconds. This output pulse is the above-mentioned comparator activation pulse 35 shown in FIG. 2B.

This comparator activation pulse 35 causes the comparator 30 to
Activate for a period equal to 215 milliseconds. Comparator 30 is an ordinary comparator that is referenced to a predetermined potential such as ground. Therefore, the comparator 30 is
The zero crossing point of the differentiated -dz/dt signal 25 is detected to produce an output pulse. The output pulse of comparator 30 is pulse 45, as shown in FIG. If the rising edge (or zero crossing) of this pulse 45 occurs within the 215 millisecond period mentioned above, it will indicate the presence of a heartbeat murmur.

Therefore, pulse 45 is sent to discriminator 50. This discriminator responds only to rising edges of the pulse that fall within a predetermined time interval. That is, discriminator 50 produces an output pulse each time there is a rising edge of a falling pulse within a predetermined time interval. Since the output pulse of this discriminator indicates the presence of heartbeat noise, it can be added to and counted by the heartbeat noise counter 60, for example, to confirm the presence of heartbeat noise. However, when there is no pulse 45 at the input of the discriminator 50, it is determined that even if the -dz/dt signal 25 is present, it does not indicate heartbeat noise, and the discriminator 50
0 generates a reset pulse and adds it to the reset input of heartbeat noise counter 60.

The heartbeat noise counter 60 receives and counts the output pulses from the discriminator 50, and when it receives a predetermined number of consecutive pulses, for example, counts 4 consecutive pulses, it issues an inhibition signal to the respiratory signal gate circuit 80, which will be described later. 70 can be generated. Other pulse numbers may be used to confirm the presence of a heartbeat murmur.

The respiration signal gate circuit 80 controls this prohibition signal 70.
, the above-mentioned respiration signal 5 is received and passed to the output terminal 90 unless the above-mentioned respiration signal 5 is present. This is the operating condition when the heartbeat murmur does not appear in a clear manner. However, the inhibition signal 7 is input to the breathing signal gate circuit 80.
If 0 is applied, no respiration signal 5 is sent to output terminal 90. Therefore, the respiratory monitor main body (not shown) connected to the output terminal 90 will not erroneously process or count heartbeat noise as a respiratory signal.

[Effect of idea]

As explained above, the present invention can reliably detect heartbeat murmurs that interfere with respiratory monitoring.
The detection results can be used to control the respiratory monitor. For example, a respiratory signal gate circuit can be provided to allow the respiratory monitor to continue operating when heartbeat murmur is unclear, and to interrupt operation of the respiratory monitor when heartbeat murmur is clear. Therefore, it is possible to prevent harmful effects caused by misinterpreting heartbeat murmurs as breathing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a preferred embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of FIG. Figure 4 is a waveform diagram showing a typical respiratory signal.
A waveform diagram showing a typical ECG signal having a QRS complex waveform, and FIG. 5 is a block diagram showing an example of a waveform processing circuit used in the present invention. 5... Respiratory signal, 10... Waveform processing circuit, 15
... QRS trigger pulse, 25 ... Output signal that emphasizes the negative slope of a predetermined value or more in the respiratory signal,
30... Comparator, 35... Comparator activation pulse, 4
0... Comparator operating circuit, 45... Output pulse of comparator 30, 50... Discriminator.

Claims (1)

[Scope of Claim for Utility Model Registration] A respiratory monitor that monitors a patient's respiratory movement by measuring its thoracic impedance change, which receives a respiratory signal from a respiratory movement measurement device based on the thoracic impedance change, and receives a respiratory signal from a respiratory movement measurement device based on the thoracic impedance change, a waveform processing circuit that detects a negative slope of the output signal and generates an output signal; a comparator connected to the waveform processing circuit that detects a zero crossing point of the output signal and generates an output pulse; and a patient's electrocardiogram signal. a comparator activation circuit that generates a comparator activation pulse having a predetermined duration and supplies the pulse to the comparator in response to a QRS trigger pulse generated immediately after the QRS complex of the comparator; and generating an output pulse indicative of the presence of heartbeat murmur when the rising edge of the output pulse from the comparator occurs within the duration of the comparator actuation pulse; a discriminator that generates a reset signal when the comparator does not occur within the duration of the comparator activation pulse; A respiratory monitor comprising: a heartbeat noise counter that generates a prohibition signal when a heart rate noise counter reaches a heartbeat noise counter; and a respiratory gate circuit that prohibits the respiratory signal from being transmitted to the respiratory monitor main body by the prohibition signal.