Systems and methods using flexible capacitve electrodes for measuring biosignals

• US 20120101357A1
• Filed: 05/17/2010
• Published: 04/26/2012
• Est. Priority Date: 05/15/2009
• Status: Active Grant

• Current Assignee: Nox Medical
• Original Assignee: Nox Medical
• Inventors: Hoskuldsson, Sveinbjorn, Gudmundsson, Bjorgvin
• Granted Patent: US 9,192,316 B2
• Time in Patent Office: Days
• US Class Current: 600/382
• CPC Class Codes: A61B 2562/0214 Capacitive electrodes
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion
• CPC Class Codes: A61B 5/25 Bioelectric electrodes therefor
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/291 for electroencephalography [EEG]
• CPC Class Codes: A61B 5/296 for electromyography [EMG]
• CPC Class Codes: A61B 5/302 for capacitive or ionised electrodes, e.g. metal-oxide-semiconductor field-effect transistors [MOSFET]
• CPC Class Codes: A61B 5/4806 Sleep evaluation A61B5/4821 takes precedence; devices for inducing sleep A61M21/02
• CPC Class Codes: A61B 5/6804 Garments; Clothes
• CPC Class Codes: A61B 5/6805 Vests
• CPC Class Codes: A61B 5/6823 Trunk, e.g., chest, back, abdomen, hip
• CPC Class Codes: A61B 5/6831 Straps, bands or harnesses
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured

Abstract

A system is provided for measuring biometric signals, including at least two electrodes, wherein at least one is a capacitive electrode with a flexible structure, the system having a circuit for measuring the voltage between the two electrodes, where in some embodiments both electrodes are capacitive electrodes, and can be arranged as flexible belts, the system being suitable for measuring ECG signals and can be configured to measure also respiratory effort with Respiratory Inductive Plethysmography (RIP) technology, using the same electrodes which are used for measuring capacitively the ECG signals, a method being further provided for measuring biosignals with the system of the invention, the method further including generating an added current signal with a signal generator connected to the circuit, where the added signal has a frequency substantially removed from the frequency of the biosignal of interest, and by measuring the voltage signal of the frequency component corresponding to the added current signal one can determine fluctuations in the overall impedance and fluctuations in the capacitance of the circuit, and correct for fluctuations in the capacitance to obtain a corrected voltage signal representing the measured biosignal.

Claims

1. A system for measuring biometric signals, comprising at least two electrodes, at least one of which is a capacitive electrode with a flexible structure, the system having a circuit for measuring the voltage between said at least two electrodes.

2. The system of claim 1 comprising at least two flexible capacitive electrodes.

3. The system of claim 2, wherein said at least two capacitive electrodes are elastically deformable.

4. The system of claim 1, wherein said electrodes comprise at least one soft, textile-like belt.

5. The system of claim 4, wherein a conductor within said at least one belt is insulated, such that the conductor does not come in direct contact with the skin of a subject, when the belt is placed on said subject.

6. The system of claim 2, comprising two flexible conducting electrodes that can be placed tightly on the body of a subject.

7. The system of claim 6, wherein said flexible conducting electrodes are configured to be placed around the torso of a subject, around the thorax and abdomen respectively, of the subject.

8. The system of claim 1, configured for determining electrocardiography (ECG) signals through measurement of voltage between said electrodes.

9. The system of claim 8, for further determining simultaneously a respiratory effort of the patient.

10. The system of claim 9, where said electrodes form belts for determining respiratory effort based on Respiratory Inductive Plethysmography.

11. The system of claim 9, comprising one or more piezo-elements for measuring respiratory effort.

12. The system of claim 9, comprising resistive polymer sensors configured for measuring respiratory effort.

13. The system of claim 10, where the required belt-to-belt insulation is achieved by using electronic transformers for an RIP signal.

14. The system of claim 10 wherein said belts are configured to form capacitive strap electrodes to measure electromyography (EMG) signals.

15. The system of claim 10 wherein said belts are configured to form capacitive electrode caps.

16. The system of claim 1, comprising means for correcting measured biosignal for fluctuations in a capacitance in the circuit.

17. The system of claim 16, comprising a signal generator for generating an added known form current signal to the biosignal, and means for measuring a voltage signal including a sum of an added signal and the biosignal of interest, and means for splitting the measured signal into the biosignal component and the added signal component.

18. The system of claim 17, wherein said added current signal has a frequency of about 50 Hz or higher.

19. The system of claim 1, comprising a high-input impedance amplifier.

20. A method for measuring biosignals from a subject, comprising:

placing at least one flexible capacitive electrode on the subject, connected in a circuit,

measuring voltage between said at least one flexible capacitive electrode and a reference point and leading the signal to a high-input impedance amplifier, and

processing the received signal and outputting a useful biosignal.

21. The method of claim 20, wherein said reference point is a second capacitive electrode comprising a flexible capacitive electrode.

22. The method of claim 20, further comprising

generating a known added current signal with a signal generator connected to said circuit, said added signal having a shape separable from the biosignal of interest,

measuring a voltage signal of the added component corresponding to the added current signal to thereby determine fluctuations in overall impedance and fluctuations in capacitance of the circuit,

correct for fluctuations in the capacitance to obtain a corrected voltage signal representing the measured biosignal and outputting said signal.

23. The method of claim 20, wherein said biosignals are electrocardiographic signals.

24. The method of claim 22, wherein the added current signal has a frequency of above about 50 Hz.

25. The method of claim 20, further comprising measuring signals indicating respiratory effort of the subject.

26. The method of claim 25, wherein said signals are measured through Respiratory Inductive Plethysmography, using said same capacitive electrode and said reference point being an electrode, both of said electrodes forming induction belts.

27. The method of 25, wherein said signals indicating respiratory effort of the subject are measured with one or more piezo-elements.

28. The method of 25, wherein said signals indicating respiratory effort of the subject are measured with one or more resistive polymer sensors.