METHOD AND SYSTEM FOR MONITORING SLEEP

• US 20100031959A1
• Filed: 03/06/2008
• Published: 02/11/2010
• Est. Priority Date: 03/07/2007
• Status: Active Grant

• Current Assignee: Baxter Healthcare SA (Baxter International Inc.), Baxter International Inc.
• Original Assignee: Cheetah Medical Ltd. (Baxter International Inc.)
• Inventors: Squara, Pierre, Burkhoff, Daniel, Avidor, Yoav, Keren, Hanan
• Granted Patent: US 8,764,667 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/145 Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissuemeasuring of blood pressure or blood flow A61B5/02; non-radiation detecting or locating of foreign bodies in blood A61B5/06
• CPC Class Codes: A61B 5/4818 Sleep apnoea

Abstract

A method of monitoring sleep of a sleeping subject is disclosed. The method comprises determining a phase shift of input radiofrequency signals received from the subject during sleep relative to output radiofrequency signals transmitted to the subject during sleep, calculating cardiac output based on the phase shift, and using the cardiac output for identifying sleep apnea events.

Claims

1. A method of monitoring sleep of a sleeping subject using output radiofrequency signals transmitted to the subject during sleep and input radiofrequency signals received from the subject during sleep, the method comprising:

determining a phase shift of the input radiofrequency signals relative to the output radiofrequency signals;

calculating cardiac output based on said phase shift; and

using said cardiac output for identifying sleep apnea events.

2. The method of claim 1, further comprising supplementing said cardiac output with blood oxygen content, wherein said identification of said sleep apnea events is based on said cardiac output and said blood oxygen content.

3. A method of monitoring sleep of a sleeping subject, comprising:

transmitting output radiofrequency signals to the subject during sleep;

receiving input radiofrequency signals from the subject during sleep; and

executing the method of claim 1.

4. The method of claim 3, further comprising measuring blood oxygen content and supplementing said cardiac output with blood oxygen content, wherein said identification of said sleep apnea events is based on said cardiac output and said blood oxygen content.

5. The method of claim 1, further comprising inputting or estimating hemoglobin concentration of the sleeping subject, wherein said identification of said sleep apnea events is based on said cardiac output and said hemoglobin concentration.

6. The method of claim 5, further comprising estimating total oxygen delivery and generating a wakening signal when an estimated value is below a predetermined threshold.

7. The method of claim 6, wherein said identification of said sleep apnea events is further based on said estimated value of said total oxygen delivery.

8. The method of claim 6, further comprising controlling positive airway pressure delivered to the sleeping subject based on said estimated value.

9. The method of claim 1, further comprising reducing or eliminating amplitude modulation of said input radiofrequency signals so as to provide input radiofrequency signals of substantially constant envelope.

10. The method of claim 1, further comprising mixing said output radiofrequency signals and said input radiofrequency signals so as to provide a mixed radiofrequency signal, and filtering out a portion of said mixed radiofrequency signal so as to substantially increase a signal-to-noise ratio of a remaining portion of said mixed radiofrequency signal.

11. The method of claim 1, further comprising applying a dynamically variable filter.

22. The method of claim 1, wherein said cardiac output is calculated using a linear relationship between said phase shift and said cardiac output.

23. The method of claim 11, wherein said dynamically variable filter is adapted in response to a change in a physiological condition of the subject.

24. The method of claim 23, wherein said physiological condition is a heart rate of the subject.

25. The method of claim 24, wherein a lower frequency bound characterizing said filter is about 0.9*(HR/60) Hz at all times, wherein said HR is said heart rate in units of beats per minute.

26. The method of claim 24, wherein an upper frequency bound characterizing said filter is about 6+1.5*[(HR/60)−

1] Hz at all times, wherein said HR is said heart rate in units of beats per minute.

12. Apparatus for monitoring sleep of a sleeping subject using output radiofrequency signals transmitted to the subject during sleep and input radiofrequency signals received from the subject during sleep, the apparatus comprising:

a phase shift determinator configured for determining a phase shift of the input radiofrequency signals relative to the output radiofrequency signals;

a cardiac output calculator configured for calculating cardiac output based on said phase shift; and

a sleep apnea identification unit configured for identifying sleep apnea events based on said cardiac output.

13. A system for monitoring sleep of a sleeping subject, comprising:

a radiofrequency generator for generating output radiofrequency signals;

a plurality of electrodes designed for transmitting said output radiofrequency signals to the subject and for sensing input radiofrequency signals from the subject; and

the apparatus of claim 12.

14. The system of claim 13, further comprising a blood oxygen measuring device.

15. The apparatus of claim 12, wherein the apparatus further comprises a total oxygen delivery estimator configured for estimating total oxygen delivery.

16. The apparatus of claim 15, wherein said sleep apnea identification unit is configured to identify said sleep apnea events based on an estimated value of said total oxygen delivery and said cardiac output.

17. The apparatus of claim 12, wherein the apparatus further comprises a closed-loop control unit configured for receiving estimated value of said total oxygen delivery and controlling pressure delivered by a respiratory therapy device based on said estimated value.

19. The apparatus of claim 12, wherein the apparatus further comprises an envelope elimination unit designed and configured for reducing or eliminating amplitude modulation of said input radiofrequency signals so as to provide input radiofrequency signals of substantially constant envelope.

20. The apparatus of claim 12, wherein the apparatus further comprises:

a mixer configured for mixing said output radiofrequency signals and said input radiofrequency signals, to provide a mixed radiofrequency signal; and

a radiofrequency filter for filtering out a portion of said mixed radiofrequency signal so as to substantially increase a signal-to-noise ratio of a remaining portion of said mixed radiofrequency signal.

21. The apparatus of claim 12, wherein the apparatus further comprises a filtering unit configured for filtering said input signals using dynamically variable filter.

27. The system of claim 13, wherein the apparatus further comprises a closed-loop control unit configured for receiving estimated value of said total oxygen delivery and controlling pressure delivered by a respiratory therapy device based on said estimated value.

28. The system of claim 27, further comprising said respiratory therapy device.

18. (canceled)