WO2004075738A2 - Method and apparatus for continuous electrode impedance monitoring - Google Patents
Method and apparatus for continuous electrode impedance monitoring Download PDFInfo
- Publication number
- WO2004075738A2 WO2004075738A2 PCT/US2004/006272 US2004006272W WO2004075738A2 WO 2004075738 A2 WO2004075738 A2 WO 2004075738A2 US 2004006272 W US2004006272 W US 2004006272W WO 2004075738 A2 WO2004075738 A2 WO 2004075738A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- signal
- test signal
- physiological
- component
- test
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims description 19
- 238000012544 monitoring process Methods 0.000 title description 10
- 238000012360 testing method Methods 0.000 claims abstract description 58
- 238000001914 filtration Methods 0.000 claims description 3
- 239000013078 crystal Substances 0.000 abstract description 3
- 230000008859 change Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 238000010998 test method Methods 0.000 description 1
- 238000012956 testing procedure Methods 0.000 description 1
- 230000001960 triggered effect Effects 0.000 description 1
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
- A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
- A61B5/6843—Monitoring or controlling sensor contact pressure
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/25—Bioelectric electrodes therefor
- A61B5/276—Protection against electrode failure
Definitions
- the present invention relates to a method and apparatus for ensuring the accuracy of an acquired physiological signal. More specifically, the present invention is a method of monitoring electrode impedance while receiving an electromagnetic physiological signal.
- Physiological monitors will often have a testing procedure to check whether the interface between a sensor and the patient being monitored is adequate to acquire a physiological reading. This is especially true with regards to the acquisition of an electrophysiological signal.
- an electrophysiological signal is acquired through an electrode which is attached to the patient.
- the contact between an electrode and a patient's skin can significantly affect the results of an electrophysiological signal.
- High contact impedance generally causes poor quality recordings due to power interference.
- Electrophysiological signals such as EEG, ECG, EOG and EMG are often distorted by the test current utilized during the test. Consequently, the prior art devices have been unable to continuously monitor the contact impedance between the electrode and the patient.
- the present invention is a method and apparatus for continuously monitoring a test signal while simultaneously acquiring a physiological signal.
- the impedance test methods currently employed in electrophysiological recording equipment cause interference to the signal being recorded because the test signal has a frequency (or frequencies in the case of non-sinusoidal test waveforms) within the frequency band of the electrophysiological signal.
- a digital signal processor DSP
- a digital band pass filter of the DSP can be used to extract the impedance test signal and electrode impedance from the received signal.
- 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 includes 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 test signal comprised of a sine wave having a known frequency and voltage amplitude.
- the test signal is passed 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.
- the present invention can be adapted to be integrated into an electrophysiological monitoring system such as EEG, EOG, EMG, and ECG.
- EEG electrophysiological monitoring system
- EOG EOG
- EMG EMG
- ECG electrophysiological monitoring system
- a display can be used to monitor both the physiological signal and the contact impedance.
- FIG. 1 is a block diagram of one embodiment of the present invention.
- FIG. 2 is a graph of the relationship between a test frequency and a frequency of an electrophysiological signal.
- FIG. 3 is a block diagram of a system employing one embodiment of the present invention.
- FIG. 4 is an embodiment of a display in one embodiment of the present invention.
- the present invention is a method and apparatus for change in electrode impedance monitoring via a combined test and physiological signal. While the embodiment disclosed is particularly adapted to monitor contact impedance and EEG, ECG, EOG, or EMG signals, one skilled in the art can readily adapt the present invention to monitor different parameters which involve the testing of a sensor that is acquiring a physiological signal.
- the present invention includes a test signal generator capable of producing an impedance test signal comprising of a sine wave having a known frequency, fz 3, which is slightly higher than the frequency range of the electrophysiological signal being monitored.
- a crystal oscillator 12 provides a known, frequency stable signal to clock the input of a counter 14.
- the counter output sequentially accesses a lookup table 16 which can be implemented using any digital storage device such as an EPROM or RAM, containing a sine waveform in digital format.
- the lookup table 16 output is then applied to a digital to analog converter (DAC) 18.
- the output of the DAC is low pass filtered using a conventional analog filter 20 to produce a sine wave of frequency, fz, and voltage amplitude Vz.
- a resistor, Rdl with a resistance many times higher than the desired electrode impedance range, converts Vz into a test current Iel .
- This current flows through the electrode, represented in Figure 1 by Zel, to produce a voltage, Vel, at the input of amplifier 22.
- Vel voltage
- Vsl electrophysiological signal
- the combined signal of Vel + Vsl is amplified and then low pass filtered by anti-aliasing filter 24 before being converted into a digital signal by analog to digital converter (ADC) 26.
- ADC analog to digital converter
- the resultant digital signal is read by a digital signal processor (DSP) 30 via multiplexor 28.
- Figure 1 shows the concept of the present invention extended to n electrode channels, using a separate ADC 26 for each channel, but a single ADC with an analog multiplexor would work equally well.
- the ADC sampling frequency should be greater than twice fz to prevent aliasing.
- the DSP 30 should have sufficient computational power to execute both filters for all channels at the desired sample rate plus any storage or display functions. It should be noted that the DSP 30 could alter the sampling frequency, fs, signal bandwidth, fo, and impedance test frequency, fz, provided the relationship to each other is maintained as per Figure 2.
- the combined signal can be isolated into the test signal component and the electrophysiological component by filtering the combined signal at appropriate frequencies.
- the DSP 30 digitally low pass filters the combined signal using a filter with a -3dB point, fo, which is lower than the impedance test frequency, fz as shown in Figure 2.
- the physiological signal, Vsl, alone is the output of the low pass filter.
- the low pass filter should have a sharp roll-off characteristic so that the test signal component at fz is completely removed.
- the filter should also have a linear phase characteristic so the physiological signal is not distorted.
- a symmetrical FIR filter finite impulse response
- the DSP 30 also digitally bandpass filters the combined signal using a filter with a center frequency of fz, the same as the test frequency.
- the output of this filter is Vel, as the physiological signal and any higher frequency noise has been removed by the bandpass filter.
- the bandpass filter may be implemented as either an FIR or an IIR (infinite impulse response) if shorter computation time is needed.
- Vel will be 50microvolts pk-pk per kilohm of electrode impedance.
- the impedance of each electrode could be displayed numerically on a computer monitor connected to the DSP ( Figures 3 and 4) or used to activate indicators such as light emitting diodes attached to the amplifier circuit enclosure should the impedance exceed a pre-determined threshold.
- the present invention can be adapted to be integrated into an electrophysiological monitoring system 30 such as EEG, EOG, EMG, and ECG.
- EEG electrophysiological monitoring system
- EOG electronic glycol
- EMG electrophysiological monitoring system
- ECG electrophysiological monitoring system
- a display 32 can be used to monitor both the physiological signal and the contact impedance.
- the electrophysiological monitor system 30 may also communicate with a central monitoring station 34.
- the electrophysiological monitor system 30 is adapted to trigger an alarm condition at the central monitoring station 34 should the impedance of any of the electrodes exceed a pre-determined threshold for a pre-determined time (to avoid spurious values triggering the alarm).
- the operator could set the alarm threshold and the minimum time the threshold needs to be exceeded before the alarm is triggered via a computer network connection to the electrophysiological monitor system 30. This would allow an operator to monitor the contact impedance of each electrode for each patient at a central location remote from the electrophysiological monitor system 30.
Abstract
Description
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU2004215917A AU2004215917B2 (en) | 2003-02-26 | 2004-02-26 | Method and apparatus for continuous electrode impedance monitoring |
US11/205,373 US8068905B2 (en) | 2004-02-26 | 2005-08-17 | Method and apparatus for continuous electrode impedance monitoring |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US45113003P | 2003-02-26 | 2003-02-26 | |
US60/451,130 | 2003-02-26 |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2004075738A2 true WO2004075738A2 (en) | 2004-09-10 |
WO2004075738A3 WO2004075738A3 (en) | 2005-11-03 |
Family
ID=32927701
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2004/006272 WO2004075738A2 (en) | 2003-02-26 | 2004-02-26 | Method and apparatus for continuous electrode impedance monitoring |
Country Status (2)
Country | Link |
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AU (1) | AU2004215917B2 (en) |
WO (1) | WO2004075738A2 (en) |
Cited By (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1795122A1 (en) * | 2005-12-12 | 2007-06-13 | General Electric Company | Detection of artifacts in bioelectric signals |
FR2908973A1 (en) * | 2006-11-24 | 2008-05-30 | Yves Faisandier | Electrical physiological signal i.e. ECG signal, recording method for ambulatory apparatus, involves associating impedance measurement of electrodes with amplification and digitization of signal to provide signals charged with information |
WO2017222888A1 (en) * | 2016-06-22 | 2017-12-28 | General Electric Company | System and method for rapid ecg acquisition |
CN109419502A (en) * | 2017-08-29 | 2019-03-05 | 韦伯斯特生物官能(以色列)有限公司 | For sensing the medical patch of ECG signal and impedance instruction electric signal simultaneously |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US9594104B2 (en) | 2014-10-22 | 2017-03-14 | Natus Medical Incorporated | Simultaneous impedance testing method and apparatus |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4993423A (en) * | 1988-07-13 | 1991-02-19 | Physio-Control Corporation | Method and apparatus for differential lead impedance comparison |
US5042498A (en) * | 1990-04-06 | 1991-08-27 | Hewlett-Packard Company | Intelligent electrocardiogram system |
US6007532A (en) * | 1997-08-29 | 1999-12-28 | 3M Innovative Properties Company | Method and apparatus for detecting loss of contact of biomedical electrodes with patient skin |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4610254A (en) * | 1984-03-08 | 1986-09-09 | Physio-Control Corporation | Interactive portable defibrillator |
US6487449B1 (en) * | 2000-05-23 | 2002-11-26 | Ge Medical Systems Information Technologies, Inc. | Method and apparatus for reducing noise and detecting electrode faults in medical equipment |
-
2004
- 2004-02-26 WO PCT/US2004/006272 patent/WO2004075738A2/en active Application Filing
- 2004-02-26 AU AU2004215917A patent/AU2004215917B2/en not_active Ceased
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4993423A (en) * | 1988-07-13 | 1991-02-19 | Physio-Control Corporation | Method and apparatus for differential lead impedance comparison |
US5042498A (en) * | 1990-04-06 | 1991-08-27 | Hewlett-Packard Company | Intelligent electrocardiogram system |
US6007532A (en) * | 1997-08-29 | 1999-12-28 | 3M Innovative Properties Company | Method and apparatus for detecting loss of contact of biomedical electrodes with patient skin |
Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1795122A1 (en) * | 2005-12-12 | 2007-06-13 | General Electric Company | Detection of artifacts in bioelectric signals |
US7684856B2 (en) | 2005-12-12 | 2010-03-23 | General Electric Company | Detection of artifacts in bioelectric signals |
FR2908973A1 (en) * | 2006-11-24 | 2008-05-30 | Yves Faisandier | Electrical physiological signal i.e. ECG signal, recording method for ambulatory apparatus, involves associating impedance measurement of electrodes with amplification and digitization of signal to provide signals charged with information |
WO2017222888A1 (en) * | 2016-06-22 | 2017-12-28 | General Electric Company | System and method for rapid ecg acquisition |
US10278602B2 (en) | 2016-06-22 | 2019-05-07 | General Electric Company | System and method for rapid ECG acquisition |
US11051740B2 (en) | 2016-06-22 | 2021-07-06 | General Electric Company | System and method for rapid ECG acquisition |
CN109419502A (en) * | 2017-08-29 | 2019-03-05 | 韦伯斯特生物官能(以色列)有限公司 | For sensing the medical patch of ECG signal and impedance instruction electric signal simultaneously |
Also Published As
Publication number | Publication date |
---|---|
AU2004215917B2 (en) | 2008-01-10 |
AU2004215917A1 (en) | 2004-09-10 |
WO2004075738A3 (en) | 2005-11-03 |
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