Detecting Sleep Events Using Localized Blood Pressure Changes

• US 20100081943A1
• Filed: 09/30/2008
• Published: 04/01/2010
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Addison, Paul Stanley, Watson, James, Sethi, Rakesh
• Granted Patent: US 9,314,168 B2
• Time in Patent Office: Days
• US Class Current: 600/484
• CPC Class Codes: A61B 5/0059 using light, e.g. diagnosis by transillumination, diascopy, fluorescence A61B5/0093, A61B5/1455, A61B5/02416 and A61B5/0261 take precedence
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/4809 Sleep detection, i.e. determining whether a subject is asleep or not
• CPC Class Codes: A61B 5/4812 Detecting sleep stages or cycles
• CPC Class Codes: A61B 5/6816 Ear lobe
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6829 Foot or ankle
• CPC Class Codes: A61B 5/6838 Clamps or clips

Abstract

Techniques for detecting sleep events are disclosed. In some embodiments, a continuous non-invasive blood pressure (“CNIBP”) monitoring system may be used to obtain blood pressure values from a subject during a sleep study. Changes in the blood pressure over time may be determined and analyzed in order to identify a sleep event. The localized blood pressure changes may be interpreted in isolation or in combination with other signals collected from the subject.

Claims

1. A method for detecting sleep events, comprising:

detecting at least one photoplethysmograph (PPG) signal;

calculating blood pressure based at least in part on the at least one PPG signal;

determining changes in the blood pressure;

analyzing the changes in the blood pressure; and

identifying a sleep event based at least in part on the analyzed changes.

2. The method of claim 1, wherein the sleep event is selected from the group consisting of sleep arousal and sleep apnea.

3. The method of claim 1, wherein detecting the at least one PPG signal comprises:

detecting a first PPG signal from a first location on a subject; and

detecting a second PPG signal from a second location on a subject,

wherein calculating the blood pressure comprises;

detecting a first time associated with a first pulse in the first PPG signal;

detecting a second time associated with a second pulse in the second PPG signal;

determining a time difference between the first time and the second time; and

calculating the blood pressure based at least in part on the time difference.

4. The method of claim 1, wherein detecting the at least one PPG signal comprises:

detecting a first PPG signal from a first location on a subject; and

identifying at least two characteristic points in the detected PPG signal,

wherein calculating the blood pressure comprises;

determining a time difference between two of the at least two characteristic points in the detected PPG signal; and

calculating the blood pressure based at least in part on the determined time difference.

5. The method of claim 1, wherein detecting the at least one PPG signal comprises:

detecting a first PPG signal from a first location on a subject; and

determining locations of pulses in the PPG signal,

wherein calculating the blood pressure comprises;

determining an area under a portion of one of the pulses; and

calculating the blood pressure based at least in part on the area.

6. The method of claim 1, wherein determining changes in the blood pressure comprises:

calculating a first blood pressure value associated with a first time;

calculating a second blood pressure value associated with a second time;

determining a blood pressure difference between the first blood pressure value and the second blood pressure value;

comparing the blood pressure difference to a pre-defined threshold value; and

identifying a sleep event, in response to determining that the blood pressure difference is greater than the pre-defined threshold value.

7. The method of claim 1, wherein determining changes in the blood pressure comprises:

calculating a long-term average blood pressure value;

calculating a short-term average blood pressure value;

determining a blood pressure difference between the long-term average blood pressure value and the short-term average blood pressure value;

comparing the blood pressure difference to a pre-defined threshold value; and

identifying a sleep event in response to determining that the blood pressure difference is greater than the pre-defined threshold value.

8. The method of claim 1, wherein determining changes in the blood pressure comprises:

starting a counter;

calculating a first blood pressure value associated with a first time;

calculating a second blood pressure value associated with a second time;

determining a time difference between the first time and the second time;

determining a blood pressure difference between the first blood pressure value and the second blood pressure value;

calculating a ratio of the blood pressure difference to the time difference;

comparing the ratio to a first pre-defined threshold value; and

identifying a sleep event, in response to determining that the ratio continues to be greater than the first pre-defined threshold value and that the counter is greater than a second pre-defined threshold value.

9. The method of claim 1, wherein determining changes in the blood pressure comprises:

detecting a first blood pressure value associated with a first time when the blood pressure begins to change significantly;

detecting a second blood pressure value associated with a second time when the blood pressure begins to stabilize;

determining a time difference between the first time and the second time;

determining a blood pressure difference between the first blood pressure value and the second blood pressure value;

comparing the time difference to a first pre-defined threshold value and the blood pressure difference to a second pre-defined threshold value; and

identifying a sleep event, in response to determining that the first time is less than the first pre-defined threshold value and the blood pressure difference is greater than the second pre-defined threshold value.

10. A system for detecting sleep events comprising:

a sensor capable of detecting at least one photoplethysmograph (PPG) signal; and

a processor capable of;

calculating blood pressure based at least in part on the at least one PPG signal;

determining changes in the blood pressure;

analyzing the changes in the blood pressure; and

identifying a sleep event based at least in part on the analyzed changes.

11. The system of claim 10, wherein the sleep event is selected from the group consisting of sleep arousal and sleep apnea.

12. The system of claim 10, wherein the processor is further capable of:

detecting a first PPG signal from a first location on a subject;

detecting a second PPG signal from a second location on a subject;

detecting a first time associated with a first pulse in the first PPG signal;

detecting a second time associated with a second pulse in the second PPG signal;

determining a time difference between the first time and the second time; and

calculating the blood pressure based at least in part on the time difference.

13. The system of claim 10, wherein the processor is further capable of:

detecting a first PPG signal from a first location on a subject;

identifying at least two characteristic points in the detected PPG signal;

determining a time difference between two of the at least two characteristic points in the detected PPG signal; and

calculating the blood pressure based at least in part on the determined time difference.

14. The system of claim 10, wherein the processor is further capable of:

detecting a first PPG signal from a first location on a subject;

receiving locations of pulses in the PPG signal;

determining an area under a portion of one of the pulses; and

calculating the blood pressure based at least in part on the area.

15. The system of claim 10, wherein the processor is further capable of:

calculating a first blood pressure value associated with a first time;

calculating a second blood pressure value associated with a second time;

determining a blood pressure difference between the first blood pressure value and the second blood pressure value;

comparing the blood pressure difference to a pre-defined threshold value; and

identifying a sleep event, in response to determining that the blood pressure difference is greater than the pre-defined threshold value.

16. The system of claim 10, wherein the processor is further capable of:

calculating a long-term average blood pressure value;

calculating a short-term average blood pressure value;

determining a blood pressure difference between the long-term average blood pressure value and the short-term average blood pressure value;

comparing the blood pressure difference to a pre-defined threshold value; and

identifying a sleep event, in response to determining that the blood pressure difference is greater than the pre-defined threshold value.

17. The system of claim 10, wherein the processor is further capable of:

starting a counter;

calculating a first blood pressure value associated with a first time;

calculating a second blood pressure value associated with a second time;

determining a time difference between the first time and the second time;

determining a blood pressure difference between the first blood pressure value and the second blood pressure value;

calculating a ratio of the blood pressure difference to the time difference;

comparing the ratio to a first pre-defined threshold value; and

identifying a sleep event, in response to determining that the ratio continues to be greater than the first pre-defined threshold value and that the counter is greater than a second pre-defined threshold value.

18. The system of claim 10, wherein the processor is further capable of:

detecting a first blood pressure value associated with a first time when the blood pressure begins to change significantly;

detecting a second blood pressure value associated with a second time when the blood pressure begins to stabilize;

determining a time difference between the first time and the second time;

determining a blood pressure difference between the first blood pressure value and the second blood pressure value;

comparing the time difference to a first pre-defined threshold value and the blood pressure difference to a second pre-defined threshold value; and

identifying a sleep event, in response to determining that the time difference is less than the first pre-defined threshold value and the blood pressure difference is greater than the second pre-defined threshold value.

19. Computer-readable medium for use in detecting sleep events, the computer-readable medium having computer program instructions recorded thereon for:

detecting at least one photoplethysmograph (PPG) signal;

calculating blood pressure based at least in part on the at least one PPG signal;

determining changes in the blood pressure;

analyzing the changes in the blood pressure; and

identifying a sleep event based at least in part on the analyzed changes.