Stretchable electrode and method of making physiologic measurements

Abstract

A stretchable electrode for use in physiologic measurements on a human body, such as peripheral impedance plethysmography, is disclosed. One embodiment of the stretchable electrode comprises an uninsulated stainless steel wire braid formed into a tubular conductor surrounding an elastic core and attached to an elastic substrate or base. Other embodiments of the stretchable electrode include a garter spring, a flat braided or woven conductor and an undulating wire. The electrode may be placed about a limb of a human body and elastically stretched so that the conductor is in substantially continuous circumferential electrical contact with the skin of the limb. A method of attaching the stretchable electrode to the limb of a human body is also disclosed.

Description

REFERENCE TO RELATED APPLICATIONS[0001]The following commonly assigned patent applications disclose and claim subject matter related to the subject matter of the present invention: U.S. patent application Ser. No. 10 / 392,308, filed Mar. 20, 2003, entitled “Peripheral Impedance Plethysmography Electrode and System with Detection of Electrode Spacing;” U.S. patent application Ser. No. 10 / 673,167, filed Sep. 30, 2003, entitled “Methods of Diagnosis Using Pulse Volume Measurement;” U.S. patent application Ser. No. 10 / 673,328, filed Sep. 30, 2003, entitled “Signal Averaging Using Gating Signal Obtained from Autocorrelation of Gating Signals;” and U.S. patent application Ser. No. 10 / 759,130, filed Jan. 20, 2004, entitled “Method and Device for Measuring Peripheral Vascular Function.” The disclosures of those applications are hereby incorporated by reference in their entireties into the present application.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present inventio...

AI Technical Summary

Benefits of technology

[0019]The stretchable conductive electrode of the first embodiment may be used for making physiologic measurements by, for example, wrapping four electrodes circumferentially about a limb of a patient to form a quadripolar electrode system useful in making impedance plethysmograph measurements as described above. Preferably, the electrodes are secured about the limb by any suitable means in a slightly stretched condition to assure that the metal of the conductor is in substantially continuous circumferential contact with the limb and, therefore, make a reliable low impedance electrical contact with the skin of the limb.

[0021]If necessary or desired, the electrodes may be slightly moistened with water to improve the electrical contact between the uninsulated metal wires and the skin, i.e., lower the impedance. Alternatively, the elastic base is moisture impervious or can be made from a moisture impervious material so that when the stretchable conductive electrode is wrapped, for example, about a limb, the elastic base covers the electrode and an annular portion of the skin adjacent the circumferential electrode contact area. Because the annular skin portion is covered by the moisture impervious base, it will tend to perspire more than it would if left uncovered. Such perspiration will, in most cases, provide sufficient moisture to improve the conductivity between the electrode and the skin, i.e., lower the impedance between the electrode and the skin.

[0023]According to a second embodiment of the invention, the electrode can be constructed in the form of a garter spring made from uninsulated stainless steel wire with a very small pitch, preferably a pitch no greater than the diameter of the wire, i.e., with adjacent coils touching. The pitch should necessarily be small so as to avoid pinching the skin between the coils of wire. In the case of the second embodiment, the spring itself is inherently elastic so that it is not necessary to provide an axial restoring force such as the elastic core of the first embodiment.

[0032]The stretchable electrode of the invention also is advantageously used in a quadripolar electrode system. As previously mentioned, because the limbs of the body are not truly cylindrical, but are shaped more in the form of truncated cones, the circumferential lengths of the electrodes in a quadripolar electrode system must differ to account for the different circumferences of the limb along its length. Because the electrodes of the invention are elastic or stretchable, when arranged in a quadripolar electrode array, they are able to make reliable, substantially continuous and uniform, circumferential electrical contact with the skin of the limb at each axial position along the limb.

Problems solved by technology

This will result in inaccurate measurements.

Disposing of multiple quadripolar electrodes for these tests would be prohibitively expensive.

With respect to a quadripolar electrode system, from a practical standpoint, it is not desirable for the user to have to place four separate electrodes on each limb to create the quadripolar arrangement but, rather, to place each current-voltage pair together in a single array.

Because the braided electrode is stretched out before it is applied to the skin of the neck and thorax, it has no restoring force that aids in maintaining reliable low impedance contact with the skin, i.e., it is not elastic.

The conductive loop is not, however, elastic or stretchable along the axial length of the conductor, nor does it make electrical contact with the skin of the subject.

The foregoing and other prior art electrodes used in physiologic measurements have not provided a reusable electrode that is characterized by a reliable low impedance electrical contact with the skin.

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