Monitoring systems

Details Monitoring systems Monitoring systems

1994-10-06

1998-05-12

Nasser, Robert L.

Surgery

Diagnostic testing

Measuring or detecting nonradioactive constituent of body...

600372, A61B 500

Patent

active

057498326

DESCRIPTION:

BRIEF SUMMARY
This invention relates to improvements relating to monitoring systems, and more particularly to improvements relating to systems for monitoring various body parameters, and especially tissue parameters, in vivo by use of electrodes.


BACKGROUND OF THE INVENTION

It is known to use electrodes as part of systems for monitoring a variety of parameters in biological conditions or in biological products or materials, especially as sensors. An especially useful form of electrode for such purposes is in the monitoring of glucose in body fluids, for example in blood or tissue, and to do this either with samples taken from a subject and studied in vitro or by use of the electrode sensor in vivo.
However, though such electrodes work well in vitro there is a major problem in in vivo use which arises from the time required for the stabilisation of the electrode--i.e. the time required for the signals from the electrode, when placed in vivo, to reach a condition in which the signals cease changing even though the environment around the electrode is not changing. This time delay can be as much as several hours, which effectively prevents use under conditions requiring rapid deployment. Also, in the case of electrodes measuring glucose or other components involving an oxidation/reduction process, there can be a considerable depression of the signal response under in vivo conditions, so that there is poor correlation between the signals and measurements of the same amounts or concentrations of analytes under in vivo and in vitro conditions.
It can be seen that such effects are not satisfactory for accurate use in vivo and can restrict severely the usefulness of such electrodes under in vivo conditions despite their otherwise valuable properties when used under in vitro conditions.
There is, therefore, a considerable need for some form of the electrodes or method of use or which can overcome these disadvantages and allow reliable and convenient use in vivo.
The reason for this "read-out" depression of the signal from the electrode is not known, but we believe it arises from some barrier or interference to its activity which is set up when the electrode is put directly into contact with compact biological tissues when it is introduced into a bodily environment.


SUMMARY OF THE INVENTION

We have now found that these disadvantages can be overcome by introducing a liquid medium into the site in vivo at which the electrode is to be used, so that the liquid medium introduced can produce an compatible environment for the electrode. This may be as a prelude to the bodily fluids making contact with the electrode, but may be at any convenient moment before, during or after such contact.
Thus according to our invention we provide a method for using or installing an electrode in place in vivo which comprises the step of providing, at the site of introduction of the said electrode, a protecting medium which, without injuring the biological environment, suppresses the adverse depressive effect on the electrode's output induced by the hostile biological environment when it has not been modified by the protecting medium. This protecting medium may then be modified or replaced by an aqueous surrounding medium which allows the electrode to become exposed to the bodily biochemical changes of the surrounding environment which is to be monitored.
This protecting medium is found helpful by overcoming the fact that tissues themselves can present an environment low in water and high in protein and elastic connective tissue macromolecules (collagen, elastin, glycoproteins) and also surface-active proteins which tend to foul electrode surfaces. All of these distort the normal "aqueous solution" conditions used to calibrate the sensor in vitro. The protecting medium is intended to provide a protecting or less hostile environment in which the electrode can function.


DETAILED DESCRIPTION OF THE INVENTION

It is believed that this protecting medium may act in one or more ways, though they are not fully understood. The protection may be mechanical,

REFERENCES:
patent: 3912614 (1975-10-01), Spracklen et al.
patent: 4803991 (1989-02-01), Alena et al.
patent: 4813424 (1989-03-01), Wilkins
patent: 4834101 (1989-05-01), Collison et al.
patent: 5171689 (1992-12-01), Kawaguri et al.
patent: 5354448 (1994-10-01), Markle et al.

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