JPH0226485Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an impedance plethysmograph, particularly an impedance plethysmograph using a synchronous detector.

[Conventional technology]

In general, an impedance plethysmograph applies a high-frequency current to a living body, captures biological phenomena such as breathing and circulation as changes in impedance, and displays or records this. In such an impedance plethysmograph, a synchronous detection method is usually used to detect the high frequency detection signal from the living body (subject) in order to improve the S/N ratio. It is being

Incidentally, since the impedance of a living body to high-frequency current can be considered to be pure resistance, it is desirable that the waveform of the detected impedance signal has positive polarity. On the other hand, it may be desirable to set the impedance fluctuation signal derived from this impedance signal to negative polarity as necessary.

FIG. 3 is a main part block diagram showing an example of a conventional impedance plethysmograph. To make the operation easier to understand, the waveforms appearing at locations a, b, c, d, and e in FIG. 3 are expressed as a, b, and e in FIG.
Shown in c, d and e. In Figure 3, 1 is a human body as a subject, 2 and 3 are current electrodes, 4 and 5
1 is a detection electrode, 6 and 7 are a first code pair, 8 and 9 are a second code pair, 10 is a high frequency oscillator, 11 is an AC amplifier, 12 is a synchronous detector, and 13 is a filter.

Now, the first and second code pairs 6, 7 and 8,
9 are connected normally, a high frequency voltage as shown in Figure 4 a appears between the first pair of cords 6 and 7, and a high frequency current with the same waveform appears between the current electrodes 2 and 3. flows, but when the impedance between the detection electrodes 4 and 5 changes, the potential difference between the detection electrodes 4 and 5 changes accordingly, and this high-frequency current whose amplitude has changed is detected by the detection electrodes 4 and 5. is added to the AC amplifier 11. A waveform as shown in FIG. 4c appears between the second code pair 8 and 9. On the other hand, the high frequency oscillator 10 generates a rectangular wave synchronizing signal as shown in FIG. 4b in synchronization with the high frequency current and supplies it to the synchronous detector 12. The synchronous detector 12 detects only the positive side of the high frequency detection signal c amplified by the positive direction pulse of the rectangular wave synchronous signal b, and generates a detection output as shown in FIG. 4d. This detected output d passes through the filter 13 and becomes an impedance signal having a positive waveform as shown in FIG. 4e.
In this way, if the connections between the two cord pairs 6, 7 and 8, 9 are both normal, the final impedance signal waveform will always have positive polarity.

[Problem that the invention attempts to solve]

In the apparatus of FIG. 3, two code pairs 6, 7
Alternatively, if one of the cords 8 and 9 is connected incorrectly and reversed, the high frequency detection signal appearing between the cords 8 and 9 c will have a waveform whose phase is shifted by 180 degrees as shown in FIG. 4 c'. Therefore, the waveform synchronously detected by the rectangular wave synchronizing signal b becomes as shown in FIG. 4 d', and the final impedance signal waveform has negative polarity as shown in FIG. 4 e'.

In this way, with conventional devices, the displayed or recorded impedance signal waveform may have the opposite polarity due to incorrect cord connection, and to avoid this, it is necessary to connect the cord carefully.
There were some very annoying flaws.

Therefore, when the impedance signal waveform has a reverse polarity, a method of inverting the polarity of the impedance signal using an inverting amplifier may be considered, but there is a possibility that the characteristics of the output signal will change due to gain drift.

Therefore, the present invention provides an impedance plethysmograph in which the impedance signal waveform always has the desired polarity without changing its characteristics even when two pairs of cords are connected to the electrodes attached to the living body with arbitrary polarities. This is what I am trying to do.

[Means for solving problems]

The present invention includes a changeover switch that supplies a rectangular wave synchronization signal from a high-frequency oscillator to a synchronization detector either directly or via a phase inversion circuit, and a means for determining erroneous connection of either the first or second code pair. and when one of the cord pairs is erroneously connected, the changeover switch is switched to the phase inversion circuit side by the output of the erroneous cord connection determination means,
The above objectives were achieved.

[Effect]

When a misconnection of one of the first and second code pairs is determined, the phase of the rectangular wave signal for synchronous detection is reversed by 180 degrees, and the phase of the high frequency detection signal extracted by the detection electrode is reversed by 180 degrees. Even if it is reversed, the final impedance signal waveform is always kept at a predetermined positive or negative polarity.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to illustrated embodiments.

FIG. 1 is a block diagram showing a preferred embodiment of the present invention. In this figure, parts corresponding to those in FIG. 3 are given the same reference numerals. 3 in Figure 1
The difference from the diagram is that a phase inversion circuit 14, a changeover switch 15, and a polarity discrimination circuit 16 are provided. The phase inversion circuit 14 converts the rectangular wave synchronization signal (FIG. 4b) from the high frequency oscillator 10 into
The phase is reversed by 180° as shown in b′. The polarity determining circuit 16 determines the polarity of the impedance signal (e or e' in FIG. 4) output from the filter 13, and generates an output when the polarity changes, for example, when e changes to e'. A movable contact of the changeover switch 15 is connected to the synchronous detector 12, and its two fixed contacts are connected to the synchronous signal output terminal of the high frequency oscillator 10 and the output terminal of the phase inversion circuit 14, respectively. The input terminal of the phase inversion circuit 14 is connected to the synchronization signal output terminal of the high frequency oscillator 10. The movable contact (arm) of the changeover switch 15 is configured to be switched by the output signal of the polarity determination circuit 16.

Now, the polarity discrimination circuit 16 is set to produce no output when the impedance signal is of positive polarity and to produce an output when the impedance signal is of negative polarity, as shown in FIG. is connected to the synchronizing signal output side of the high frequency oscillator 10, by connecting either one of the two cord pairs 6, 7 or 8, 9, the impedance signal changes as shown in Figure 4 e'. When the polarity becomes negative, the polarity discrimination circuit 16 generates an output and switches the changeover switch 15 to the phase inversion circuit 14.
The synchronization signal for synchronous detection is switched to b in Figure 4.
The phase is reversed by 180° from b′. Synchronous detector 1
2 detects the amplified high-frequency detection signal using the positive direction pulse of the synchronization signal, so only the positive direction component of the high-frequency detection signal (Fig. 4 c') whose phase is inverted by 180° is detected. The impedance signal waveform becomes positive again.

FIG. 2 is a block diagram showing a specific example of the polarity discrimination circuit 16. In this figure, parts corresponding to those in FIG. 1 are given the same reference numerals. A comparator 17 supplies a positive reference voltage to its non-inverting (+) input, and supplies the output voltage of the filter 13 to its inverting (-) input. The comparator 17 produces a low level output when the output voltage has positive polarity, and produces a high level output when the output voltage has negative polarity. This output is applied to one input of the AND circuit 18. AND circuit 18
Since a trigger pulse f with a period T is supplied to the other input of the flip-flop 19, this trigger pulse f passes through the AND circuit 18 and inverts the output of the flip-flop 19. Although the figure shows a D flip-flop, it is not necessarily limited to this. When the output of the flip-flop 19 is inverted, the changeover switch 15 is supplied to the phase inversion circuit 14 side as shown. Here, the period T of the trigger pulse f is
It is necessary to make the time longer than the time required for the output of the filter 13 to return from negative to positive polarity after the changeover switch 15 is switched to the phase inversion circuit 14 side.

In the above, a case has been described in which the impedance signal is always of positive polarity, but as mentioned above, when displaying or recording a signal indicating impedance fluctuation derived from the impedance signal, it may be of negative polarity as necessary. There are things that are desired.
In such a case, the output of the comparator 17 in the polarity determining circuit 16 shown in FIG. 2 may be set to a low level when the impedance signal is of negative polarity.
Therefore, the "impedance signal" in this specification also includes an impedance fluctuation signal derived from the output of a synchronous detector.

In addition, in the example of Fig. 1, a polarity discrimination circuit is shown as a means for determining incorrect cord connection, but the means for determining incorrect cord connection is not limited to this, and it is possible to directly compare the phase of the high frequency detection signal and the phase of the high frequency oscillation current. do,
The changeover switch may be changed when the phases of the two are reversed by 180 degrees. In addition, as long as it falls within the scope of the utility model registration request,
Various modifications and changes are possible.

[Effect of idea]

As explained above, according to the present invention, there is no need for the operator to consider polarity at all when connecting the cord, making handling of the impedance plethysmograph extremely easy. Furthermore, compared to a method using an inverting amplifier, this method has the advantage that there is no drift in gain because the polarity is inverted by inverting the phase of the synchronizing signal, and there is no change in the characteristics of the output signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a preferred embodiment of the present invention, FIG. 2 is a block diagram showing a specific example of the polarity discrimination circuit shown in FIG. 1, FIG. 3 is a block diagram showing a conventional example, and FIG. FIG. 3 is a waveform diagram for explaining the operation of the conventional example and the embodiment. 1... Subject, 6, 7... First code pair, 1
0... High frequency oscillator, 8, 9... Second coat pair, 12... Synchronous detector, 13... Impedance signal deriving means, 14... Phase inversion circuit, 15...
...changeover switch, 16...means for determining incorrect cord connection.

Claims (1)

[Scope of utility model registration request] a high-frequency oscillator that supplies a high-frequency current to the test object via a first code pair and generates a rectangular wave synchronization signal synchronized with the high-frequency current; and a high-frequency detection signal extracted from the test object via a second code pair. In an impedance plethysmograph having a synchronous detector that detects a signal using the rectangular wave synchronous signal, and means for deriving an impedance signal from the output of the synchronous detector, the synchronous signal is detected as is or through a phase inversion circuit. a changeover switch for supplying to the detector; and polarity determining means for generating an output when the polarity of the impedance signal obtained by arbitrary connection of the first and second code pairs or any of these code pairs is a predetermined polarity. An impedance plethysmograph, comprising: an output from the polarity determining means to switch the changeover switch.