Method and apparatus for continuous electrode impedance monitoring

• US 20060020218A1
• Filed: 08/17/2005
• Published: 01/26/2006
• Est. Priority Date: 02/26/2004
• Status: Active Grant

• Current Assignee: Compumedics Limited
• Original Assignee: Compumedics Limited
• Inventors: Freeman, Warwick, Newman, Richard, Grasso, Philip
• Granted Patent: US 8,068,905 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/24 Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
• CPC Class Codes: A61B 5/276 Protection against electrode failure
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure

Abstract

In one embodiment, the present invention includes a test signal generator capable of producing an impedance test signal comprising of a sine wave having a known frequency. The test signal generator may include a crystal oscillator, a counter, and a lookup table. The lookup table output is applied to a digital to analog converter and is then low pass filtered using a conventional analog filter to produce a sine wave of a known frequency and voltage amplitude. The test signal flows through the electrode and combines with an electrophysiological signal to form a combined signal. A signal processor is used to isolate the combined signal into the test signal component and the electrophysiological component. The signal processor digitally low pass filters the combined signal and the output of the low pass filter is the electrophysiological signal. The signal processor then digitally bandpass filters the combined signal using a filter with a center frequency which is the same as the test frequency. The output of this filter is then used to calculate the electrode impedance.

Claims

1. A method comprising:

sending a test signal to a sensor of physiological data, said sensor having an impedance;

receiving a combined signal comprising a physiological signal component and a test signal component;

.

filtering the combined signal to separate the physiological signal component from the test signal component; and

detecting changes in the impedance of the sensor by a comparison of test signal components.

2. The method of claim 1, wherein the combined signal is filtered using a band pass filter to isolate the test signal component.

3. The method of claim 2, wherein the test signal is a sine wave having a known frequency.

4. The method of claim 3, wherein the step of sending a test signal includes using a sine waveform in digital format and applying the sine waveform to a digital to analog converter.

5. The method of claim 4, wherein the test signal has a higher frequency than the physiological signal component, and wherein filtering includes using a low pass filter on the combined signal to isolate the physiological signal component.

6. The method of claim 1, and further comprising determining contact impedance between the sensor and a patient'"'"'s skin from the test signal component.

7. A method comprising

communicating a test signal to a sensor of physiological data;

combining a physiological signal with the test signal to create a combined signal; and

deriving both a physiological waveform and contact impedance from the combined signal.

8. The method of claim 7, wherein deriving the physiological waveform includes utilizing a low pass filter on the combined signal to isolate a physiological component.

9. The method of claim 7, wherein deriving the contact impedance includes utilizing a band pass filter on the combined signal to isolate a test signal component.

10. The method of claim 7, and further comprising simultaneously displaying the physiological waveform and the contact impedance from the combined signal.

11. The method of claim 7, and further comprising creating an analog test signal having a known frequency by storing a sine wave in digital format and using a digital to analog converter to convert the stored digital sine wave into an analog signal.

12. An apparatus comprising;

a test signal generator adapted to deliver a test signal to a sensor;

a signal processor adapted to receive a combined signal from the sensor and isolating the combined signal into a physiological component and a test signal component; and

a display adapted to display a physiological waveform derived from the physiological component and a contact impedance derived from the test signal component.

13. The apparatus of claim 12, wherein the test signal generator includes an oscillator, a counter, and a lookup table adapted to create a sine wave in digital format.

14. The apparatus of claim 13, wherein the test signal generator includes a digital to analog converter in communication with the lookup table.

15. The apparatus of claim 12, wherein the signal processor includes a band pass filter adapted to isolate the test signal component.

16. The apparatus of claim 15, wherein the signal processor includes a low pass filter adapted to isolate the physiological component.

17. The apparatus of claim 12, wherein the sensor is an electrode.

18. The apparatus of claim 12, wherein the test signal generator, the signal processor and the display are adapted into an EEG machine.

19. The apparatus of claim 12, wherein the test signal generator, the signal processor and the display are adapted into an ECG machine.

20. The apparatus of claim 12, wherein the test signal generator, the signal processor and the display are adapted into an EMG machine.

21. The apparatus of claim 12, wherein the test signal generator, the signal processor and the display are adapted into an EOG machine.