Surgery – Truss – Pad
Patent
1995-09-06
1997-02-18
Millin, Vincent
Surgery
Truss
Pad
G06F 1542
Patent
active
056033338
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an impedance catheter for measuring electrical impedances in blood vessels, within an annular region around the catheter, the catheter containing excitation electrodes, which are connected to an alternating current source and with measuring electrodes between which a potential difference can be measured.
Measuring that electrical impedance is important for the diagnosis of patients with vascular diseases: by means of the value of the impedances along a vessel route affected by constrictions and/or obstructions, it may be possible in combination with data obtained from X-ray photos or ultrasonography to determine the fat content of the material that causes these constrictions and/or obstructions, without the patient being required to undergo surgery. Actually, the specific electrical impedance of fat is much higher than that of blood, vascular tissue, etcetera.
Atherosclerosis is by far the most occurring form of appearance of coarctation in human beings. In particular this occurs in the abdominal aorta and in the femoral artery with diameters of approximately 5 mm and 3 mm respectively. The importance of information about the fat content in an atherosclerotic lesion is connected with the fact that lesions, rich in fat are less firm of substance than those poor in fat, which makes it easier for them to be torn open, at which a very thrombogenic material is released.
Until now it appeared impossible with the existing diagnostic techniques to distinguish in a reliable manner lesions rich in fat over those poor in fat.
Also adaptation of standard impedance catheterization did not lead to the desired result. Impedance catheterization is a method, at which two excitation electrodes are connected to an alternating current source and the circuit is closed because the current can flow to and fro between the electrodes through the environment in which the catheter is located.
Between de excitation electrodes there are two (or more) measuring electrodes. The voltage difference between those measuring electrodes is a measure for the electrical impedance in the field of current. That this well-known method for measuring impedances did not lead to the intended aim, lies in the fact that one cannot find out whether a change in the impedance takes place near the catheter, in the blood vessel, or farther away, in the tissue next to the blood vessel. Hence conclusions with respect to the blood vessel whether or not being stenosized can not be drawn.
The invention is based on the insight that by using a specific impedance catheter it is possible to determine changes in the impedance in `inner region` and `outer region` separately. To that end two current sources are used that are connected to two sets of excitation electrodes in such a way and are actuated with such a relation of the respective current intensities that around the catheter a pattern of electrical field lines is generated, a so-called counter current field, at which through variation of the amplitude of the currents of a set of excitation electrodes as regards the other set it will be possible to see to it that between the measuring electrodes no, or hardly any current runs and at a larger distance of the measuring electrodes the electrical field lines are mainly perpendicular to the longitudinal axis of the catheter and that the average impedance of the area to be measured and that of the area outside this will be measured separately, by choosing the relation of the current intensities in such a way that it deviates from the relation at which there is no current between the measuring electrodes, the quenching relation, and by adjusting that relation exactly to that quenching relation respectively.
The two current sources are connected and actuated, as it were, `wrongly`, which causes the `counter current field` to come into existence around the catheter. When such a catheter, adjusted in such a way that there is no or hardly any current flowing between the measuring electrodes, passes a deviating impedance in the small area near the c
REFERENCES:
patent: 3452743 (1969-07-01), Rieke
patent: 4840182 (1989-06-01), Carlson
patent: 4852580 (1989-08-01), Wood
N. Furuya et al., "Development of multielectrode impedance plethysmography", Medical and Biological Engineering and Computing, vol. 24, No. 1, Jan. 1986, pp. 62-70.
Academisch Ziekenhuis Utrecht
Millin Vincent
Wieland Robert N.
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