AU5069685A

AU5069685A - Apparatus and method for monitoring organs of the body

Info

Publication number: AU5069685A
Application number: AU50696/85A
Authority: AU
Inventors: John Andrew Sutton
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-11-15
Filing date: 1985-11-15
Publication date: 1986-06-03
Also published as: JPS62501267A; GB2190751B; GB8428831D0; EP0235137A1; GB2190751A; WO1986002819A1; GB8711445D0

Description

- 1 -

APPARATUS AND METHOD FOR MONITORING ORGANS OF THE BODY

This invention relates to apparatus for monitoring hollow visceral organs of the body.

This invention is based on the observation that it is possible to monitor body function, for example, the function of hollow visceral organs such as the stomach including measuring the volume of the heart, lungs, bladder and uterus dand the volume of fluid within any of these organs, electronically, by measuring differences in impedance across the body through the organ in question using a plurality of electrodes.

According to the invention apparatus for monitoring body functions comprises oscillator means for generating a high frequency oscillation, an oscillator driven constant current generating source, at least one pair of current driven electrodes for attachment to the body of a patient, at least two pairs of voltage sensing electrodes for attachment to the body of the patient, tuner/voltage amplifier means tuned to the frequency of the generator means, converter means for measuring impedance changes registering between pairs of voltage sensing electrodes, impedance indicator means isolating circuit means for receiving signals from the impedance converter, filter means for excluding electronic or biological fluctuations from the equipment or the subject and an impedance offset control, and recorder means for recording the subject signals, the subject signals being received by the recorder means as separate signals.

The recorder means may, for example, comprise a chart recorder or oscilloscope, a tape recorder or a microcomputer and preferably in addition to having the capability for receiving the signals from the different electrode pairs separately also has the capability of correcting phase displacement between the signals and recording a combination of the signals. - 2 - The apparatus can be used to monitor, for example, size, rate of filling or emptying and wall contraction in hollow visceral organs of the body, for example, the stomach, heart, lungs, bladder and uterus.

The recording produced by the recorder gives a continuous reading of impedance changes. It shows a base line with fluctuations indicating contractions in the wall of the organ causing changes in impedance. When the organ fills the trace rises to a maximum and then decreases towards a base level value, the subsiding trace similarly being superimposed by fluctuations indicating contractions in the wall of the organ. Filling and emptying times of the organ are shown by the speed of ascent to a peak and subsequent decline. Volume can be determined as a function of the magnitude of change of impedance. The magnitude of contractions of the wall are shown as a function of the area of the minor peaks superimposed on the main trace. Processing, for example, by Fourier analysis of the signals indicates contractions of the organ in different regions covered by the electrode and by dividing the trace into, for example, time intervals, differences in contractions at different times can be determined giving an indication of, for example, response to a meal or drugs or other stimulus.

The trace produced by combining the signals from a large number of electrodes gives an indication of the full impedance displacement of the organ and therefore gives a more sensitive indication of the volume that can be derived from the separate signals.

In one specific form of the apparatus, the generator means is a 100 kHz oscillator and the current control means produces a 4 milliamp peak-to-peak constant current drive.

A non-invasive method for monitoring stomach volume and rate of filling and/or emptying has long been sought by gastroenterological physicians. A non-invasive method has the advantages of repeatability unlike X-ray or isotopic methods so that the progress of illness or the effects of treatment can be measured. The new device proposed has this capability and has proved so sensitive in practice that it may also be used to quantify the contractions of the stomach. Because pairs of electrodes can be used separately to monitor stomach contractions the progress of contractions through the stomach can be assessed. At the same time because a plurality of electrodes is used the accuracy of the volume measurement is enhanced by surveying an increased region of the body thus including the entire region of the stomach even though the exact position of the stomach cannot be identified from without.

Further, the use of at least two pairs of voltage sensing electrodes increases the possibility of recording signals from the region of interest, within the body, which cannot be identified from without.

Moreover, whereas impedance methods have been proposed for monitoring rates of change of cardiac volume and therefore the power of contraction and heart muscle the results have not been quantifiable. Therefore accurate measurements of the volume of blood ejected by the heart, known as cardiac output, have not been feasible. If electrodes of the new device are placed over the stomach and a measured volume of water or other suitable liquid drunk the impedance change can be measured so that impedance changes can be related to the volume drunk. Thus, when other electrodes are used to record the cardiac volume changes the results obtained can be quantified by reference to the recorded gastric change results. In this way a new, non-invasive device for monitoring cardiac performance is available.

Further, in any measurements of function where reference, comparison, or standardisation between signals from the organ being monitored and any other region of the body is required, additional sets of electrodes are used.

The invention will now be described in greater detail by way of example with reference to the drawing which shows a block diagram of a single channel circuit showing only one pair of voltage sensing electrodes; whereas in practice at least two voltage sensing channels would be used. In the drawing, 1 is a 100 kHz oscillator,

2 is a 4 milliamp peak-to-peak constant current drive, 3 is the stomach, 4 is a pair of current driving electrodes, 5 is a pair of voltage sensing electrodes, 6 is a 100 kHz tuner/voltage amplifier,

7 is a detector to recover impedance changes, 8 is an impedance meter, 9 is a subject signal isolation amplifier, 10 is a low pass filter and impedance offset control, 11 is a chart recorder and 12 is a tape recorder or microcomputer.

In using the apparatus the current driving and voltage sensing electrodes 4 and 5 are placed on the body of the patient around the organ to be monitored. The signal recorded by the voltage sensing electrodes 5 is passed to the amplifier 6 and converted to impedance by detector/converter 7. The signal from the detector/converter 7 is passed both to impedance meter 8 which gives a direct read out of impedance and to trhe signal isolation amplifier 9 and thence to the low pass filter and recorder. When more than one voltage sensing channel is used the signals from the separate pairs of voltage sensing electrodes are maintained separate and are individually passed to the recorder so that impedance changes detected by each pair of voltage sensing electrodes can be recorded individually. The recorder, however, preferably also includes means for correcting phase displacement of the individual signals and combining the signals so that the total of the impedance changes recorded by a number of electrodes can also be indicated by the recorder.

Figs. 2 and 3 are more detailed self-explanatory circuit diagrams in which like reference numerals have been used to indicate the various components of the apparatus. It will be appreciated that only one set of electrodes 5 is shown in these figures and the circuitry will be duplicated as appropriate to accommodate from the sets of electrodes 5.

It will also be appreciated that the circuitry shown is merely exemplary of one especially preferred embodiment of the invention - 5 - and the invention is not to be regarded in any way as limited to the arrangement shown.

Claims

- 6 -C L A I M S

1. Apparatus for monitoring body functions comprising oscillator means for generating a high frequency oscillation, an oscillator driven constant current generating source, at least one pair current driven electrodes for attachment to the body of a patient, at least two pairs of voltage sensing electrodes for attachment to the body of the patient, tuner/voltage amplifier means tuned to the frequency of the generator means, converter means for measuring impedance changes registering between pairs of voltage sensing electrodes, impedance indicator means, isolating circuit means for receiving signals from the impedance converter, filter means for excluding electronic or biological fluctuations from the equipment or the subject and a impedance offset control, and recorder means for recording the subject signals, the subject signals being received by the recorder means as separate signals.

2. Apparatus according to claim 1, wherein the recorder means comprises a chart recorder or oscilloscope, a tape recorder or a microcomputer.

3. Apparatus according to claim 1 or claim 2, wherein the recorder, in addition to having the capability for receiving the signals from the different electrode pairs separately also has the capability of correcting phase displacement between the signals and recording a combination of the signals, and in addition means to analyse and process signals as required.

4. A method of producing a record of the function of a hollow visceral organ which comprises :

attaching at least one pair current driven electrodes to the body of a patient around the region of the organ to be monitored; attaching at least two pairs of voltage sensing electrodes to the body of the patient around the region of the organ to be monitored; - - passing an oscillated driven constant current through the current driven electrodes; measuring the voltages received by the voltage sensing electrodes; converting said voltages to determine impedance through the organ; separately passing signals correlated to the impedance values recorded by said electrodes to a recorder and producing a continuous record of changes of impedance through the organ.

5. A method according to claim 4, wherein the separate signals produced from the voltage sensing electrodes are corrected for phase displacement and are combined to produce a record corresponding to the combination of the impedance changes across the organ.

6. A method according to claim 4, wherein the separate signals produced from the voltage sensing electrodes are processed separately In order to quantify the changes in impedance, in various regions of the organ of interest, as, for example, in the determination of volume, magnitude and periodicity of contraction, emptying and filling rates.

7. A method according to claim 4 or claim 5 or claim 6, wherein the impedance changes determined by a plurality of pairs of voltage sensing electrodes attached to the body around the region of the organ of interest are compared, standardised or combined with the signals obtained from an additional set of electrodes attached to a different part of the body.