Method and apparatus for detecting loss of contact of biomedical electrodes with patient skin

• US 6,007,532 A
• Filed: 08/29/1997
• Issued: 12/28/1999
• Est. Priority Date: 08/29/1997
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Netherly, Samuel G.
• Primary Examiner(s): Dvorak, Linda C. M.
• Assistant Examiner(s): GIBSON, ROY DEAN
• Application Number:
  US08/924,037
• Time in Patent Office: 851 Days
• Field of Search: 606/32, 606/35
• US Class Current: 606/35
• CPC Class Codes: A61B 18/1233 with circuits for assuring patient safety
• CPC Class Codes: A61B 18/16 Indifferent or passive electrodes for grounding
• CPC Class Codes: A61B 5/276 Protection against electrode failure
• CPC Class Codes: A61N 1/046 Specially adapted for shock therapy, e.g. defibrillation
• CPC Class Codes: A61N 1/0492 Patch electrodes A61N1/0412, A61N1/0428 take precedence

Abstract

A method of monitoring the contact of a biomedical electrode to skin of a patient is disclosed, where at least two different frequencies are employed to periodically monitor total contact impedance of the electrode. The ratio of the change of the total contact impedances over time can then be monitored to indicate the amount of lift of the biomedical electrode from human skin to which it is supposed to be adhered. Lift of any portion of the electrode from contact with skin of a patient can be monitored more easily than using conventional Contact Quality Monitoring circuitry and "split plate patient plates."

Claims

1. A method of detecting loss of contact between a biomedical electrode and skin of a patient, comprising the steps of:

(a) detecting total contact impedance of the electrode using two different frequencies to establish two initial total contact impedances;

(b) detecting two total contact impedances of the electrode using the same frequencies as in step (a) at at least one later time to establish two differences in total contact impedance, one difference for each frequency; and

(b) sounding an alarm when the ratio of change of the contact impedances exceeds a predetermined amount.

2. A method of quantifying lift off of a biomedical electrode from skin of a patient, by the use of the equation:

space="preserve" listing-type="equation">Degree of Lift=(Z.sub.f1t0 -Z.sub.f1t1)/Z.sub.f2t0 -Z.sub.f2t1)

where Z denotes a total contact impedance of the biomedical electrode, f1 denotes a first impedance measurement frequency, f2 denotes a second impedance measurement frequency, to denotes a first (or initial) impedance measurement time, and t1 denotes a impedance measurement at some later time, comprising the steps of (a) measuring two initial total contact impedances using two different frequencies, (b) measuring two later time total contact impedances using the same two frequencies as in step (a) and using the equation to obtain a ratio of change of the two total contact impedances; and

(c ) sounding an alarm when the ratio of change of the two total contact impedances exceeds a certain set value.

3. A method of determining the amount of skin contact between a biomedical electrode and skin of a patient, comprising the steps of:

(a) measuring the ratio of the change of two total contact impedances, measured at different frequencies, over time of an energized biomedical electrode; and

(b) sounding an alarm when the ratio of the change of the total contact impedances over time exceeds a predetermined amount.

4. An apparatus for detecting loss of contact between a biomedical electrode and skin of a patient, comprising:

(a) a biomedical electrode having an electrical conductor having at least a portion thereof having lossy dielectric properties; and

(b) means for measuring contact impedance at two different frequencies;

(c) means for detecting when a ratio in the change of total contact impedances measured at two different frequencies over time exceeds a predetermined amount.