WO2003059165A1

WO2003059165A1 - Bioimpedance measurements

Info

Publication number: WO2003059165A1
Application number: PCT/NL2003/000028
Authority: WO
Inventors: Hendrik Gebhard Goovaerts
Original assignee: A.J. Van Liebergen Holding B.V.
Priority date: 2002-01-18
Filing date: 2003-01-17
Publication date: 2003-07-24
Also published as: NL1019788C2; AU2003203307A1

Abstract

The invention relates to a method for electronically measuring a parameter of, for example, a mechanical system such as an electromechanical system or of a human body, wherein an excitation voltage or excitation current from an excitation source is supplied at a predetermined signal frequency to the examined object or body, and a resulting measuring value is determined, which forms a gauge for the magnitude of the parameter, wherein to determine the signal frequency of the excitation source, first a preceding measurement is carried out on the object or body, to detect signal frequencies of, for example, interference sources or other measurements, and that subsequently the signal frequency of the excitation source is determined at a value that prevents interference with the signal frequencies already present.

Description

BIOIMPEDANCE MEASUREMENTS

The invention relates to a method for electronically measuring a parameter of, for example, a mechanical system such as an electromechanical system or of a human body, wherein an excitation voltage or excitation current from an excitation source is supplied at a predetermined signal frequency to the examined object or body, and a resulting measuring value is determined, which forms a gauge for the magnitude of the parameter.

As far as the determination of a biomedical para e- ter of a human body is concerned, such a method is known for example from applicant's earlier international patent application PCT/NL96/00374.

A problem that may occur with the precise determination of such a parameter is that interference is caused by locally present interference sources or simultaneous measurements on a body, applying a neighbouring signal frequency. The undesirable consequence that must be avoided is, that the determination of the magnitude of the parameter is negatively influenced and may produce an incorrect value, which may have very detrimental consequences for the further treatment.

It is the object of the invention to provide the solution to the problems just mentioned.

To this end the method proposed by the invention is characterized in that to determine the signal frequency of the excitation source, first a preceding measurement is carried out on the object or body, to detect signal frequencies of, for example, interference sources or other measurements, and that subsequently the signal frequency of the excitation source is determined at a value that prevents interference with the signal frequencies already present.

By this in retrospect incredibly simple measure, the problems posited can be completely eliminated. According to common practice, the excitation source used for the measurement has a predetermined range of signal frequencies . In order to fully benefit from the significance of the invention with respect to the quality of the final measurement, the predetermined measurement is preferably carried out over the entire range of signal frequencies from the excitation source. This is the best possible way for taking advantage of the possibilities available for guaranteeing an interference-free measurement. In practical terms the invention may suitably be realized such that the preceding measurement is carried out using a signal source provided with a controllable frequency sweep, wherein the signal from the signal source is multiplied by a passive signal measured on the object or body, in order to obtain an indicator signal constituting a measure for those frequencies from the frequency sweep that are also noticeably present in the signal measured on the object or body, and that the signal frequency of the excitation source is adjusted so as to be different therefrom. To further elucidate the invention, the same will be illustrated below with reference to an exemplary embodiment that is of course not limiting with respect to the scope of protection defined by the claims following the example.

Non-limiting exemplary embodiment

The invention relates to the scanning of signal frequencies present in the working range of a measuring device, for example, a bio-impedance measuring device that estimates parameters relating to the heart function. This concerns signal frequencies that are present in the measuring signal when the measuring device is connected to the patient. The invention provides a method of determining a workable measuring frequency that will not interfere with the frequen- cies already measured passively on the patient.

In practical terms, the existence of this problem can be illustrated by the necessity of simultaneously monitoring both the patient's heart function and respiration. Usually the respiratory function is monitored using a low excitation current of a frequency in the range between 40 kilohertz and 80 kilohertz. The heart function is monitored by means of another system with which excitation voltages of frequencies in the above-mentioned range, for example, 64 kilohertz are generated.

In order to arrive at a correct frequency setting in relation to, for example, the heart function measuring device, an assessment is first made in the entire frequency range of this device to establish which frequencies are already in use for taking measurements on the patient or are present as ambient interference signals . This may conveniently be realized by using the so-called heterodyne principle; that is to say by multiplying passively measured frequency components obtained from the patient with a precisely known signal source, whose frequency is derived from, for example, an internal oscillator or synthesizer. The resulting product signal forms an indication for the frequencies already used because if the frequency of the known signal source corresponds to the passively measured frequencies, this product signal produces high values. These frequency values may be stored in the memory as frequencies that are not available for measuring the heart function.

For example, if the respiration monitor apparatus is operating at a frequency of 64 kilohertz, the device for determining the heart function can be adjusted to a value different from this frequency value, for example, 63 kilohertz or 65 kilohertz. This deviation with respect to the usual measuring frequency of 64 kilohertz is sufficiently small to not affect the precision of determination of the respective heart parameter.

Claims

1. A method for electronically measuring a parameter of, for example, a mechanical system such as an electromechanical system or of a human body, wherein an excitation voltage or excitation current from an excitation source is supplied at a predetermined signal frequency to the examined object or body, and a resulting measuring value is determined, which forms a gauge for the magnitude of the parameter, characterised in that to determine the signal frequency of the excitation source, first a preceding meas- urement is carried out on the object or body, to detect signal frequencies of, for example, interference sources or other measurements, and that subsequently the signal frequency of the excitation source is determined at a value that prevents interference with the signal frequencies already present .

2. A method according to claim 1, wherein the excitation source has a predetermined range of signal frequencies, characterised in that the predetermined measurement is carried out over the entire range of signal frequencies from the excitation source.

3. A method according to claim 1 or 2 , characterised in that the preceding measurement is carried out using a signal source provided with a controllable frequency sweep, wherein the signal from the signal source is multiplied by a passive signal measured on the object or body, in order to obtain an indicator signal constituting a measure for those frequencies from the frequency sweep that are also noticeably present in the signal measured on the object or body, and that the signal frequency of the excitation source is ad- justed so as to be different therefrom.