METHOD AND KIT FOR SWEAT ACTIVITY MEASUREMENT

• US 20100179403A1
• Filed: 07/01/2008
• Published: 07/15/2010
• Est. Priority Date: 07/02/2007
• Status: Active Grant

• Current Assignee: Universitetet I Oslo (Kunnskapsdepartementet)
• Original Assignee: Biogauge - Nordic Bioimpedance Research AS
• Inventors: Grimnes, Sverre Joran, Martinsen, Orjan Grottem, Fosse, Erik
• Granted Patent: US 8,565,850 B2
• Time in Patent Office: Days
• US Class Current: 600/346
• CPC Class Codes: A61B 2562/0217 Electrolyte containing
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/0531 Measuring skin impedance
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4035 Evaluating the autonomic nervous system
• CPC Class Codes: A61B 5/4266 sweat secretion

Abstract

The invention relates to sweat activity measurement, e.g. for determining a physiological state of a subject, embodied by a method as well as a kit with an immittance measuring circuit and electrodes with contact electrolyte. Sweat activity is considered a transport phenomenon and can be defined as a flux, e.g. gram water per skin area per second. Prior art methods determining water absorbed per gram dry stratum corneum measures skin moisture and do not truly reflect sweat activity. A periodic signal with frequency of 60 Hz or lower is applied to reduce contribution from complex admittance of the skin, and skin conductance is measured as a degree of sweat activity. The contact electrolyte allows filling of sweat ducts with sweat from sweat glands, this may be characterized in that it does not substantially fill the sweat ducts when being positioned on the skin and/or in that it has a re-absorption time constant from the sweat ducts into the Epidermis of less than 15 min.

Claims

1. A kit for monitoring sweat activity, comprising an electronic processing unit for measuring a conductance signal and a set of three electrodes to be positioned on skin sites of a subject;

the electrodes being supplied with contact electrolyte for providing electrical contact between the electrodes and the skin sites, the contact electrolyte being characterized in that it allows filling of sweat ducts with sweat from sweat glands over the course of the monitoring when being positioned on the skin sites;

the electronic processing unit comprising an electrode drive circuit for applying a periodic signal with a predetermined frequency of less than 60 Hz to at least one of the electrodes to reduce the contribution from the stratum corneum complex admittance, and an immittance measuring circuit for measuring at least a conductance signal received from at least one of the electrodes.

2. The kit according to claim 1, wherein the contact electrolyte is an electrically conductive solid gel.

3. The kit according to claim 1, wherein the electronic processing unit comprises a sweat activity change estimation module configured to determine, by signal analysis, a coefficient of change in sweat activity versus time.

4. The kit according to claim 3, wherein the change estimation module is adapted to identify fluctuations in the conductance signals and to use the identified level of such fluctuations as measure of sweat activity.

5. The kit according to claim 1, wherein the electronic processing unit comprises a frequency analysis module for performing frequency analysis of the conductance signal in order identify an activity level of the subject based on the frequency content of the signals.

6. The kit according to claim 1, wherein the electronic processing unit also uses the DC voltage component generated by the skin under the measuring electrode.

7. The kit according to claim 1, comprising a stratum corneum moisture content estimation module and a conductance correction module for correcting the conductance determined by the electronic processing unit using the determined moisture content to determine a quantitative expression for the sweat activity.

8. A method for determining a physiological state of a subject by registering sweat activity caused by the sympathetic nervous system, the method comprising applying the kit according to claim 1 to monitor sweat activity.

9. The method according to claim 8 wherein the physiological state is related to blood sugar.

10. The method according claim 8, wherein sweat activity is monitored for two or more different skin sites of the subject and for which the electronic processing unit of the kit is connected to corresponding two or more sets of electrodes, and wherein each set of electrodes represents a separate monitoring channel.

11. The method according to claim 8, wherein the sweat activity is monitored over a period of time to determine a coefficient of change in sweat activity as a function of time.

12. The method according to claim 8, comprising a frequency analysis of the registered sweat signal in order to identify an activity level, e.g. high activity or low activity, for the subject being monitored.

13. The method according to claim 8, further comprising:

determining a moisture content in the stratum corneum, and correcting the conductance determined by the electronic processing unit using the determined moisture content to determine a quantitative expression for the sweat activity.

14. The method according to claim 8, further comprising measurement of endogenous dc voltage.

15. A method for monitoring sweat activity of a subject over time, the method comprising:

providing an electronic processing unit for measuring a conductance signal and a set of three electrodes to be positioned on skin sites of a subject,

arranging the electrodes in electric contact with the skin via a contact electrolyte having the property of allowing filling of sweat ducts with sweat from sweat glands in the skin sites over the course of the monitoring when being positioned on the skin sites;

applying a periodic signal with a predetermined frequency of less than 60 Hz to the electrodes to reduce the contribution from the stratum corneum complex admittance; and

measuring at least a conductance signal received from the electrodes.