JP6131016B2 - Bioimpedance measurement device - Google Patents

Description

  The present invention relates to a bioimpedance measuring apparatus.

  2. Description of the Related Art Conventionally, an apparatus that measures lung impedance of a living body using electrodes implanted in a coronary vein and a left chest wall with a lung in between is known (for example, see Patent Document 1). The lung impedance includes information on the blood volume of the lung, and changes periodically according to the increase or decrease in the blood volume of the lung accompanying the pulsation of the heart. That is, since the lung impedance amplitude reflects cardiac output, cardiac function can be evaluated by monitoring lung impedance over time.

JP 2008-168120 A

However, the lung impedance obtained by actual measurement includes components derived from changes in breathing and heart pulsation in addition to lung blood volume, and components derived from other than the lung blood volume are components of the lung. If it is large relative to the components derived from blood volume, it is difficult to accurately analyze changes in lung blood volume. As a result, there is a problem that the cardiac function cannot be accurately evaluated.
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a bioimpedance measuring apparatus capable of remarkably capturing changes in the amplitude of lung impedance due to changes in cardiac function.

In order to achieve the above object, the present invention provides the following means.
The present invention includes a housing including a can electrode implanted in a chest wall, a pair of electrodes provided on the distal end side of a lead extending from the housing and inserted into a coronary vein, and insulated from each other, and one of the pair of electrodes A constant current supply unit that supplies a constant current between the pair of electrodes, a voltage measurement unit that measures a voltage between the other of the pair of electrodes and the can electrode, and a pair of constant current supply units. An impedance calculation unit that calculates an impedance using a constant current supplied between the one of the electrodes and the can electrode and a voltage measured by the voltage measurement unit, the pair of electrodes both The electrode has a length dimension that can be accommodated in the coronary vein in the longitudinal direction of the lead, and at least one of the pair of electrodes is in a state where blood flow to the lung is reduced from a normal state And Of the amplitude of the impedance are calculated by the impedance calculation unit, a said length dimension, such as do not overlap each other range of variability due to variations in the noise component other than the blood flow of the lung, 15 mm or more 150mm or less of the A bioimpedance measuring device having a length dimension is provided.

  According to the present invention, a current supply unit supplies a constant current between a can electrode and one electrode disposed opposite to each other across the lung in a living body, and the can electrode and the other electrode generated across the lung By the voltage measuring unit measuring the voltage between the impedance, the impedance calculating unit can calculate the lung impedance.

  In this case, the impedance calculated by the impedance calculation unit includes components derived from breathing, heart pulsation, electrical noise, and the like other than the lung blood volume (hereinafter collectively referred to as noise components). The impedance amplitude also varies due to noise components. According to the present invention, the difference in amplitude between two impedances obtained in a normal state in which the cardiac function is normal and a heart failure state in which the cardiac function is reduced is less than the variation in the amplitude of the impedance caused by the fluctuation of the noise component. The electrodes are long enough to be large. Thereby, the change in the amplitude due to the change in the cardiac function can be recognized remarkably in the lung impedance waveform calculated by the impedance calculation unit.

In the above invention, at least one of the pair of electrodes is 1 . The outer diameter may be 52 mm or more and 5 mm or less.
In this way, the difference in lung impedance amplitude obtained between the normal state and the heart failure state can be made sufficiently larger.

In the above invention, at least one of the pair of electrodes may have a conductive wire spirally wound in the circumferential direction of the lead.
In this way, the electrode has a flexible structure, and the electrode can be easily bent along the shape of the coronary vein in the coronary vein.

  According to the present invention, there is an effect that the change in the amplitude of the lung impedance due to the change in the cardiac function can be recognized remarkably.

1 is an overall configuration diagram of a bioimpedance measurement apparatus according to an embodiment of the present invention. It is a block diagram which shows the function of the bioelectrical impedance measuring apparatus of FIG. It is a graph which shows the lung impedance in the normal state (before pulmonary blood flow interruption | blocking) and the heart failure state (after pulmonary blood flow interruption | blocking) measured using the ring electrode of a different length dimension. It is a graph which shows the relationship between the length dimension of a ring electrode, and the amplitude of lung impedance. It is a graph which shows the relationship between the length dimension of a ring electrode, and the change rate of the amplitude of the lung impedance in a normal state and a heart failure state. It is a block diagram which shows the modification of the bioimpedance measuring apparatus of FIG. It is a graph which shows the lung impedance before (a) removal of the respiratory fluctuation component by the heart rate adaptive filter of FIG. 6, and (b) after removal. It is a block diagram which shows the modification of a can electrode. It is a graph which shows the lung impedance (upper stage) and the electrocardiogram signal (lower stage) in the normal state and the heart failure state which were measured using different combinations of electrodes for supplying alternating constant current and measuring voltage. It is a block diagram which shows the modification of a tip electrode and a ring electrode. It is a block diagram which shows another modification of a tip electrode and a ring electrode. It is a figure which shows the modification of the bioimpedance measuring apparatus of FIG. 1 provided with three electrodes. It is a figure which shows another modification of the bioimpedance measuring apparatus of FIG. 1 provided with three electrodes.

Hereinafter, a bioimpedance measuring apparatus 1 according to an embodiment of the present invention will be described with reference to the drawings.
The bioimpedance measurement apparatus 1 according to the present embodiment supplies, for example, a high voltage pulse or a pacing pulse for pacing a heartbeat to the heart A, thereby treating heart failure such as fibrillation or tachycardia. As shown in FIG. 1, a housing 2 implanted in the left chest wall and a lead 3 extending from the housing 2 and inserted into the coronary vein via the superior vena cava, right atrium and coronary sinus as shown in FIG. And.
The housing 2 is made of metal, and the housing 2 itself functions as the can electrode 4.

  The lead 3 includes a pair of electrodes 5 and 6 at the tip portion. One electrode is a tip electrode 5 provided at the tip of the lead 3, and the other electrode is a ring electrode 6 provided on the proximal end side of the tip electrode 5. The tip electrode 5 and the ring electrode 6 are insulated from each other.

  The chip electrode 5 has a cylindrical shape that covers the outer peripheral surface of the lead 3. The outer diameter of the tip electrode 5 is 1.5 mm or more and the inner diameter of the applied coronary vein (for example, 5 mm for humans) or less. The length dimension of the chip electrode 5 (dimension in the direction along the longitudinal direction of the lead 3) is, for example, 1 mm.

  The ring electrode 6 is a coil electrode in which a conducting wire is spirally wound in the circumferential direction of the lead 3. The outer diameter of the ring electrode 6 is 1.52 mm or more and the inner diameter of the coronary vein to be applied, as with the tip electrode 5. The center distance (pitch) between adjacent conductors of the ring electrode 6 is preferably narrower, and more preferably the conductors are tightly wound without a gap.

  In addition, as will be described in detail later, the length dimension of the ring electrode 6 is a range of variation in the amplitude of lung impedance measured when the cardiac function is normal (normal state), and the cardiac function is reduced. It is equal to or more than the dimension that can be separated from the range of variation in the amplitude of the lung impedance measured when the subject is in a heart failure state, and is equal to or less than the length that can be accommodated in the coronary vein. Specifically, the length dimension of the ring electrode 6 is 15 mm or more and 150 mm or less.

  Thus, even if the length of the ring electrode 6 is sufficiently larger than the length of the coronary vein, the ring electrode 6 made of a coil electrode has flexibility, so that it easily follows the shape of the coronary vein. Can be curved. As the structure of the ring electrode 6, a structure other than the coil electrode may be adopted as long as it has a flexible structure that can be bent along the shape of the coronary vein.

FIG. 2 is a diagram illustrating a detailed configuration of the bioimpedance measurement apparatus 1.
As shown in FIG. 2, the bioimpedance measuring apparatus 1 includes a high-frequency constant current circuit (constant current supply unit) 7 connected between the can electrode 4 and the ring electrode 6, the can electrode 4, and the tip electrode 5. A differential amplifier 8 connected between the two, a band-pass filter 9 connected to the differential amplifier 8, and an impedance calculator 10 for calculating lung impedance are provided inside the housing 2. Between the can electrode 4 and the chip electrode 5 and the differential amplifier 8, an amplifier (not shown) for amplifying signals detected by the electrodes 4 and 5 may be provided.

  The high frequency constant current circuit 7 supplies an alternating constant current of 2 kHz to 20 kHz between the can electrode 4 and the ring electrode 6. The voltage generated between the can electrode 4 and the chip electrode 5 by the supply of the AC constant current is input to the band pass filter 9 as an output voltage from the differential amplifier 8, and is converted into an AC constant current by the band pass filter 9. After removing other than the corresponding frequency band, the voltage in the frequency band corresponding to the AC constant current is sent to the impedance calculation unit 10. The voltage input to the impedance calculation unit 10 in this way is linearly correlated with the impedance of the lung B sandwiched between the can electrode 4 and the tip electrode 5.

  The impedance calculation unit 10 uses the value of the voltage input from the bandpass filter 9 and the value of the AC constant current supplied between the can electrode 4 and the ring electrode 6 by the high-frequency constant current circuit 7 to determine the lung impedance. Is calculated. The calculated lung impedance is stored, for example, in a time series in a storage device (not shown) for a certain period, and then read out to an external device to be used for evaluating the function of the heart A.

Next, the operation of the bioimpedance measuring apparatus 1 configured as described above will be described.
The bioimpedance measuring apparatus 1 according to the present embodiment measures lung impedance by using a can electrode 4 and a pair of electrodes 5 and 6 that are arranged to face each other with a lung B interposed therebetween. Specifically, an AC constant current is supplied from the high-frequency constant current circuit 7 between the can electrode 4 and the ring electrode 6, and the voltage between the can electrode 4 and the tip electrode 5 is used as the output voltage of the differential amplifier 8. obtain. The voltage obtained by the differential amplifier 8 is sent to the impedance calculation unit 10 through the band pass filter 9 and is used for calculation of lung impedance in the impedance calculation unit 10.

  Here, the lung impedance periodically changes as the blood volume of the lung B increases or decreases. The amplitude of the lung impedance at this time reflects the cardiac output. That is, the lung impedance amplitude increases in a normal state where the heart A pump function is normal, and the lung impedance amplitude decreases in a heart failure state where the heart A pump function is low. Therefore, a user such as a doctor can evaluate the cardiac function of the living body in which the bioimpedance measuring apparatus 1 is implanted by paying attention to the amplitude of the lung impedance and continuously observing the transition of the amplitude. .

  FIG. 3 shows lung impedance measured using ring electrodes 6 of different length dimensions. In the upper part, the lung impedance measured in the normal state where the blood flow circulates in the lung B is shown. In the lower part, the pulmonary impedance measured in a state where the pulmonary artery is blocked and the circulation of blood flow to the lung B is stopped in order to create a pseudo heart failure state is shown. Both the upper and lower lung impedances were measured with breathing stopped. As shown in FIG. 3, the measured lung impedance includes a noise component derived from the pulsation of heart A, electrical noise, and the like in addition to the component derived from the blood flow volume of lung B.

  Note that the conditions for measuring the lung impedance shown in FIG. 3 are as follows. The ring electrode 6 was a conductor having a wire diameter of 0.1 mm to 0.5 mm and an outer diameter of 1.56 mm, and the conductor was tightly wound without a gap. The can electrode 4 was a substantially rectangular parallelepiped having a vertical dimension of about 50 mm, a horizontal dimension of about 40 mm, and a thickness dimension of about 8 mm. The AC constant current supplied between the can electrode 4 and the chip electrode 5 by the high-frequency constant current circuit 7 was 300 μA.

  FIG. 4 is a graph showing the relationship between the amplitude of the lung impedance obtained by the measurement of FIG. 3 and the length dimension of the ring electrode 6. As shown in FIG. 4, variation in the error range indicated by the error bar occurs in the amplitude of the lung impedance. This error range is an average of ± 8%. In order to evaluate cardiac function from the amplitude of lung impedance, the range of variation in amplitude of lung impedance measured in a normal state must not overlap with the range of variation in amplitude of lung impedance measured in a heart failure state. Necessary.

  In FIG. 4, when the ring electrode 6 having a length of 9 mm is used, part of both error bars overlap. This means that it may not be possible to accurately distinguish between a normal state and a heart failure state. On the other hand, when the ring electrodes 6 having lengths of 28 mm, 38 mm, 47 mm, and 55 mm are used, the error bars are separated without overlapping. This means that even if a noise component included in the measured lung impedance is added, the normal state and the heart failure state can be reliably identified from the amplitude of the lung impedance.

  FIG. 5 calculates the change rate of the lung impedance amplitude between the normal state and the heart failure state from the amplitude of the lung impedance in the normal state and the heart failure state shown in FIG. 4, and the calculated change rate and the ring electrode 6 is a graph showing a relationship with a length dimension of 6; As shown in FIG. 5, the ring electrode 6 and the change rate of the lung impedance amplitude are linearly correlated.

Here, in order to prevent the error bars in FIG. 4 from overlapping, it is sufficient that the change rate is 16% or more, and in order to set the change rate to 16% or more, the ring electrode 6 shown in FIG. It is derived from the relationship between the amplitude of the lung impedance and the length of the ring electrode 6 that is 15 mm or more.
Thus, according to the present embodiment, by setting the length dimension of the ring electrode 6 to 15 mm or more, the change in the amplitude of the lung impedance between the normal state and the heart failure state can be recognized remarkably, and the cardiac function is improved. This has the advantage that it can be evaluated with high accuracy.

  In the present embodiment, as shown in FIG. 6, a heart rate adaptive filter 11 that removes a respiratory fluctuation component from the lung impedance calculated by the impedance calculation unit 10 is provided after the impedance calculation unit 10. It may be provided. In this case, a heartbeat detecting unit 12 that detects the heart rate of the living body in which the bioimpedance measuring apparatus 1 is implanted is also provided. For example, the heart rate detector 12 calculates the heart rate from the waveform of the electrocardiogram signal detected by the tip electrode 5 and the ring electrode 6. The heart rate adaptive filter 11 extracts a frequency band component corresponding to the frequency of the heartbeat from the lung impedance received from the impedance calculation unit 10. The frequency band corresponding to the frequency of the heartbeat is determined by using the heart rate detected by the heartbeat detecting unit 12, and is, for example, a frequency band included in a range of ± 50% from the average around the average of the heart rate. Is set.

  FIG. 7A shows an example of the lung impedance including the respiratory fluctuation component, and FIG. 7B shows the lung impedance obtained by removing the respiratory fluctuation component from the lung impedance of FIG. 7A. ing. In this way, the lung impedance component that varies in synchronization with the respiration of the living body in which the bioimpedance measuring device 1 ′ is implanted is removed, and the lung impedance component that is more accurately derived from the variation in the blood volume of the lung B. And the change in the amplitude of the lung impedance between the normal state and the heart failure state can be captured more remarkably. As a result, for example, the heart failure diagnosis unit 13 provided at the subsequent stage of the heart rate adaptive filter 11 can more accurately diagnose heart failure using lung impedance that is accurately derived from fluctuations in the blood volume of the lung B. .

  In the present embodiment, an alternating constant current is supplied between the can electrode 4 and the tip electrode 5 and the voltage between the can electrode 4 and the ring electrode 6 is measured. The combination of electrodes used for supply and voltage measurement is not limited to this.

  For example, an alternating constant current may be supplied between the can electrode 4 and the ring electrode 6 and the voltage between the can electrode 4 and the tip electrode 5 may be measured. Further, as shown in FIG. 8, when the can electrode is bipolar, it is between one of the tip electrode 5 and the ring electrode 6 and one of the can-base electrode 4a and the can-tip electrode 4b. An AC constant current may be supplied to measure a voltage between the other of the tip electrode 5 and the ring electrode 6 and the other of the can-base electrode 4a and the can-tip electrode 4b. The can-base electrode 4 a is an electrode made of the housing 2, and the can-chip electrode 4 b is an electrode provided on the housing 2 and insulated from the housing 2.

  FIG. 9 shows lung impedance (upper stage) and intracardiac electrocardiogram signal (lower stage) measured using different combinations of electrodes for supplying alternating constant current and measuring voltage. As shown in FIG. 9, the combination of the tip electrode 5 and the can-tip electrode 4b and the combination of the ring electrode 6 and the can-base electrode 4a are used for supplying an alternating constant current, and the ring electrode 6 and the can-base electrode 4a are used for voltage measurement. Even when the combination of the base electrode 4a and the combination of the tip electrode 5 and the can-tip electrode 4b are used, there is a clear difference in the lung impedance amplitude between the normal state and the heart failure state.

  As described above, even when the ring electrode 6 having a length of 15 mm or more is used for either supply of AC constant current or measurement of voltage, the same effect as that of the above-described embodiment can be obtained.

In the present embodiment, the ring electrode 6 has a length dimension of 15 mm or more. Instead, as shown in FIG. 10, the tip electrode 5 has a length dimension of 15 mm or more. It is good also as having. Moreover, as shown in FIG. 11, both the tip electrode 5 and the ring electrode 6 may have a length dimension of 15 mm or more.
Thus, when at least one of the tip electrode 5 and the ring electrode 6 disposed in the coronary vein has a length dimension of 15 mm or more, the same effect as that of the above-described embodiment can be obtained.

  In the present embodiment, the lead 3 is provided with the two electrodes 5 and 6, but may be provided with three electrodes instead. In this case, two of the three electrodes may be used for supplying an alternating current and the remaining one may be used for measuring a voltage, or two of the three electrodes may be used for measuring a voltage, The remaining one may be used for supplying AC low current. A part of the three electrodes may be used for supplying a pacing pulse to the heart A.

12 and 13 show examples of three electrodes.
In FIG. 12, a short electrode 51, a short electrode 52, and a long electrode 61 are provided in order from the tip of the lead 3. The short electrodes 51 and 52 are sufficiently short electrodes like the above-described tip electrode 5, and the long electrodes 61 are sufficiently long electrodes compared to the tip electrode 5 like the above-described ring electrode 6.

In this case, an alternating constant current is supplied between the long electrode 61 and the can electrode 4, and the voltage between the can electrode 4 and one short electrode 51/52 is measured. In addition, detection of an electrocardiogram signal and supply of a pacing pulse to the heart A are performed using the two short electrodes 51 and 52.
By doing so, it is possible to achieve both high-precision measurement of lung impedance and detection and pacing of an electrocardiogram signal. That is, by using the short electrodes 51 and 52 having a sufficiently small surface area for measurement and pacing of an electrocardiogram signal, an electrocardiogram signal with less noise can be obtained, and sufficient pacing can be performed with a low-energy pacing pulse. An effect can be obtained.

In FIG. 13, a long electrode 62, a short electrode 53, and a long electrode 63 are provided in order from the tip of the lead 3. In this case, an alternating constant current is supplied between one long electrode 62/63 and the can electrode 4, and the voltage between the can electrode 4 and the short electrode 53 is measured. Further, pacing pulses are supplied to the heart A using the short electrode 53 as a negative electrode.
In some patients, a high effect of the pacing pulse is obtained in the vicinity of the position of the short electrode 53. Therefore, pacing can be performed more effectively for such patients.

1, 1 'bioimpedance measuring device 2 housing 3 lead 4 can electrode 4a can-base electrode 4b can-chip electrode 5 chip electrode 6 ring electrode 7 high frequency constant current circuit (current supply unit)
8 Differential amplifier (voltage measurement unit)
9 Bandpass Filter 10 Impedance Calculation Unit 11 Heart Rate Adaptive Filter 12 Heart Rate Detection Unit 13 Heart Failure Diagnosis Unit A Heart B Lung

Claims (3)

A housing with a can electrode implanted in the chest wall;
A pair of electrodes provided on the distal end side of the lead extending from the housing and inserted into the coronary vein and insulated from each other;
A constant current supply unit for supplying a constant current between one of the pair of electrodes and the can electrode;
A voltage measuring unit for measuring a voltage between the other of the pair of electrodes and the can electrode;
An impedance calculation unit that calculates an impedance using the constant current supplied between the one of the pair of electrodes and the can electrode by the constant current supply unit and the voltage measured by the voltage measurement unit;
The pair of electrodes has a length dimension in the longitudinal direction of the lead, in which both the electrodes can be accommodated in the coronary vein,
At least one of the pair of electrodes is a noise other than a lung blood flow, with an amplitude of the impedance calculated by the impedance calculator in a normal state and a decreased state of blood flow to the lung. The bioimpedance measuring apparatus having the length dimension such that the ranges of variations caused by component fluctuations do not overlap each other, and the length dimension is 15 mm or more and 150 mm or less . The bioimpedance measurement apparatus according to claim 1, wherein at least one of the pair of electrodes has an outer diameter of 1.52 mm or more and 5 mm or less. At least one of the biological impedance measuring apparatus according to claim 1 or claim 2 wires is wound spirally in a circumferential direction of the lead of the pair of electrodes.

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