Surgery – Diagnostic testing – Measuring electrical impedance or conductance of body portion
Patent
1996-12-18
1998-09-15
Hindenburg, Max
Surgery
Diagnostic testing
Measuring electrical impedance or conductance of body portion
A61B 505
Patent
active
058072705
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the monitoring and management of oedema in certain tissues, in particular intracellular oedema within the brains of mammals, and the assessment of swelling following injury by me of electrical impedance measurements. It is adapted for long-term monitoring using suitable externally applied electrodes and also short-term monitoring of tissue trauma during surgery where surgical tools having embedded electrodes are used. The invention discloses mpedance monitoring equipment, and a method for use of the equipment.
BACKGROUND
The monitoring of patients with acute head injuries, whether caused by externally induced trauma such as birth or accident, or by circulatory problems, has hitherto relied upon clinical signs but these may not appear until a time at which the damage may have become at least partially irreversible.
Electroencephalography (EEG) tests preferably also including a frequency analysis device to reduce the data and indicate electrical activity is more suitable, though impractical outside a controlled environment. (Reliable EEG measurements require electrical screening from outside interference, a motionless subject, and relatively complex equipment).
Cerebral oedema is a particular problem during brain surgery, where manipulation, such as retraction of parts of the brain almost inevitably involves some alteration to the circulation of blood and extracellular fluids. At present the practice is to release retractors from time to time on an empirical basis, not knowing whether the chosen time is needlessly early or too late.
It appears that cerebral oedema is particularly significant when it occurs intracellularly, within neurones. It appears that there is a kind of "self-destruct" process affecting neurones, occurring over a period after some types of CNS injury, the effects of which can be ameliorated by clinical management.
There is a clear need for a better detection procedure for the onset of cerebral oedema, so that steps to alleviate it may be taken as soon as possible and even before the appearance of clinical signs, thereby providing for increased survival and better long-term prospects of patients.
OBJECT
It is an object of the present invention to provide an improved system for the measurement of oedema of the central nervous system, or one which will at least provide the public with a useful choice.
STATEMENT OF THE INVENTION
In one broad aspect the invention provides means capable of repeatedly measuring the impedance of the whole brain or parts thereof of living mammals, thereby indicating the state of normality of the tissues under test
More particularly the test indicates the amount of extracellular fluid present.
Preferably the measurement procedure is non-invasive and does not interfere with brain function.
In a related aspect the invention provides impedance measuring equipment suitable for use in cranial or intracranial impedance measurements of nervous tissue.
Preferably a four-electrode test arrangement is used.
Preferably a synchronous detector is used to detect an AC voltage developed as a result of an alternating current applied to the tissue under test.
Preferably the frequency used is a frequency between 3 Hz and 3 KHz.
More preferably the frequency used is between 30 Hz and 150 Hz.
Preferably the current is between ten microamperes and 0.1 microamperes.
More preferably the current is of the order of one microampere.
Preferably the current used is physiologically acceptable and is substantially below potentially harmful limits, even if used continuously over a period.
Preferably the impedance measurement is averaged over time so that artefacts resulting from effects such as pulsatile blood flow or inadvertent muscle movements are substantially not apparent.
Preferably the equipment is portable and preferably it is electrically isolated,
Optionally it may simply indicate the absence or presence of a state of oedema, though preferably an analogue indication is provided,
More preferably a graphical indication showing t
REFERENCES:
patent: 3566233 (1971-02-01), Kahn et al.
patent: 4424816 (1984-01-01), Callahan et al.
patent: 4690149 (1987-09-01), Ko
patent: 5224490 (1993-07-01), Allen et al.
Hindenburg Max
Wingood Pamela A.
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