APPARATUS FOR ELECTRODERMAL ACTIVITY MEASUREMENT WITH CURRENT COMPENSATION

• US 20140316229A1
• Filed: 03/17/2014
• Published: 10/23/2014
• Est. Priority Date: 03/16/2013
• Status: Active Grant

• Current Assignee: Empatica SRL (Empatica, Inc. (Massachusetts))
• Original Assignee: Empatica SRL (Empatica, Inc. (Massachusetts))
• Inventors: TOGNETTI, SIMONE, CENCI, IVAN, RESNATI, DANIELE, GARBARINO, MAURIZIO, LAI, MATTEO
• Granted Patent: US 10,506,944 B2
• Time in Patent Office: Days
• US Class Current: 600/383
• CPC Class Codes: A61B 2562/0215 Silver or silver chloride containing
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/0531 Measuring skin impedance
• CPC Class Codes: A61B 5/0533 Measuring galvanic skin response
• CPC Class Codes: A61B 5/6802 Sensor mounted on worn items
• CPC Class Codes: A61B 5/681 Wristwatch-type devices

Abstract

An apparatus for measuring electrodermal activity can include a first electrode in contact with a first portion and a second electrode in contact with a second portion of a stratum corneum, and in electronic communication with the second electrode through the stratum corneum. A processing module is electrically coupled to the first electrode and the second electrode and is operable to (a) bias the first electrode at a first voltage V+ and the second electrode at a second voltage V− (b) measure a current flowing between the first electrode and the second electrode, the current corresponding to the conductance of the stratum corneum, (c) subtract a compensation current from the measured current (d) measure a resulting current producing an amplified output voltage (e) measure a conductance of the stratum corneum, and (f) adjust at least one of the first voltage, the second voltage and the compensation current to desaturate the output voltage.

Claims

1. An apparatus for measuring electrodermal activity, comprising:

a first electrode in contact with a first portion of a stratum corneum of skin;

a second electrode in contact with a second portion of the stratum corneum and in electronic communication with the first electrode through the stratum corneum; and

a processing module electrically coupled to the first electrode and the second electrode and operable to (a) bias the first electrode at a first voltage V+ and the second electrode at a second voltage V−

, (b) measure a current flowing between the first electrode and the second electrode, the current corresponding to the conductance of the stratum corneum, (c) subtract a compensation current from the measured current, (d) measure a resulting current and produce an amplified output voltage, (e) measure a conductance of the stratum corneum, and (f) adjust at least one of the first voltage, the second voltage, and the compensation current to desaturate the output voltage.

2. The apparatus of claim 1, wherein the processing module is further configured to adjust the compensation current if the conductance of the stratum corneum is too low.

3. The apparatus of claim 1, wherein the processing module is further configured to measure a compensated value of conductance from which a tonic level conductance is removed.

4. The apparatus of claim 1, wherein the processing module is configured to reverse the polarity of at least one of the first electrode and the second electrode after a predetermined period of time to substantially reduce electrolysis.

5. The apparatus of claim 1, wherein the processing module is configured to allow a tuning of the compensation current that is subtracted from the current between the first electrode and the second electrode prior to amplification.

6. The apparatus of claim 1, wherein the stratum corneum is a stratum corneum of any portion of person'"'"'s skin.

7. The apparatus of claim 6, wherein the apparatus is configured to measure a tonic level conductance of the stratum corneum in the range of about 0.05 μ

S to about 50 μ

S.

8. The apparatus of claim 1, wherein the apparatus is configured to measure the conductance of the stratum corneum with a resolution of 0.0001 μ

S.

9. A wearable device for measuring electrodermal activity, comprising:

a housing configured to be removably associated with a user;

a first electrode, at least a portion of the first electrode disposed outside the housing and configured to contact a first portion of a stratum corneum of skin when the housing is associated with the user;

a second electrode, at least a portion of the first electrode disposed outside the housing and configured to contact a second portion of the stratum corneum of the skin when the housing is associated with the user;

a processing module disposed in the housing and electrically coupled to the first electrode and the second electrode, the processing module operable to (a) bias the first electrode at a first voltage V+ and the second electrode at a second voltage V−

(b) measure a current flowing between the first electrode and the second electrode, the current corresponding to the conductance of the stratum corneum, (c) subtract a compensation current from the measured current, (d) measure a resulting current and produce an amplified output voltage, (e) measure a conductance of the stratum corneum, and (f) adjust at least one of the first voltage, the second voltage, and the compensation current to desaturate the output voltage;

a communications module disposed in the housing, the communications module coupled to the processing module and configured to at least one of a display an electrodermal activity of the user, and communicate electrodermal activity data from the processing module to an external device; and

a power source disposed in the housing and configured to provide electrical power to the processing module and the communications module.

10. The wearable device of claim 9, wherein the processing module is further configured to decrease the compensation current if the conductance of the stratum corneum is too low.

11. The wearable device of claim 10, wherein the wearable device is a wrist band.

12. The wearable device of claim 11, wherein the processing module is configured to measure a tonic level conductance of the stratum corneum of the wrist of the user in the range of about 0.05 μ

S to about 50 μ

S.

14. The wearable device of claim 9, wherein the processing module is further configured to reverse the polarity of at least one of the first electrode and the second electrode after a predetermined period of time to substantially reduce electrolysis.

15. The wearable device of claim 9, further comprising a heart beat sensor.

16. The wearable device of claim 15, further comprising at least one of an accelerometer, a temperature sensor, a blood oxygen sensor, and a glucose sensor.

17. The wearable device of claim 16, wherein the communications module is configured to communicate at least one of heart beat data, an accelerometer data, a temperature data, a blood oxygen data, and a glucose data to the external device.

18. The wearable device of claim 17, where the communication module is configured to communicate with the external device via at least one of a USB, USB 2.0, IEEE 1394, BLUETOOTH®

, low powered BLUETOOTH®

, and Wi-Fi.

19. A method for measuring electrodermal activity, comprising:

disposing a first electrode and a second electrode on a stratum corneum of a user;

biasing the first electrode at a first voltage and a second electrode at a second voltage;

measuring a current flowing between the first electrode and the second electrode;

subtracting a compensation current from the current flowing between the first electrode and the second electrode to get an input current;

transforming the input current into an amplified output voltage;

measuring an output voltage;

measuring a conductance of the stratum corneum;

determining if the output voltage is saturated; and

increasing the compensation current to change the output voltage such that the output voltage is not saturated.

13. The wearable device of claim 19, wherein the wearable device is at least one of a head band, an arm band, a foot band, an ankle band, and a ring.

20. The method of claim 19 further comprising:

determining if the conductance of the stratum corneum is too low; and

decreasing the compensation current if the conductance is too low.

21. The method of claim 20, wherein the measured conductance is a tonic level conductance having a value in the range of about 0.05 μ

S to about 50 μ

S.

22. The method of claim 20, wherein the measured conductance is a phasic level conductance having a resolution up to 0.0001 μ

S.