# US 12,178,600 B2 · Wakefulness and sleep stage detection using respiration effort variability

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- Number: US 12,178,600 B2
- Document ID: US12178600B2
- Status: Granted
- Kind: B2
- Application number: 18/064,113
- Filed: 2022-12-09
- Published: 2023-06-15
- Granted: 2024-12-31
- Earliest claimed: 2021-12-10
- Assignees: Alfred E. Mann Foundation for Scientific Research
- Applicants: The Alfred E. Mann Foundation for Scientific Research
- Inventors: Brian Michael Shelton; Sahar Elyahoodayan
- Web page: https://patentgrep.com/patent/US12178600B2

## CPC

- A61B 5/4812: {Detecting sleep stages or cycles}
- A61B 5/0205: Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
- A61B 5/4809: {Sleep detection, i.e. determining whether a subject is asleep or not}
- A61B 5/6802: {Sensor mounted on worn items}
- A61B 5/02405: {Determining heart rate variability}
- A61B 5/0816: {Measuring devices for examining respiratory frequency (measuring frequency of electric signals G01R23/00)}
- A61B 5/113: occurring during breathing
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

The present disclosure generally relates to systems and methods for monitoring and/or the sleep stage of an individual using one or more sensors, and methods of treating medical conditions related thereto (e.g., obstructive sleep apnea).

## Claims

### Claim 1

A computer-implemented system for determining a level of wakefulness and/or sleep stage of a human subject, comprising:
a first sensor configured to detect a signal indicative of respiration effort by the human subject when placed on or in proximity to one or more regions of a chest and/or head of the human subject; and
a controller comprising a processor and memory, communicatively linked to the first sensor and configured to receive the signal from the first sensor indicative of respiration effort by the human subject, and to use the received signal to:
determine a mean respiration interval for a finite trailing window,
determine a number of respiration intervals within the finite trailing window that deviate from the mean respiration interval by less than a threshold parameter, and
determine a level of wakefulness and/or sleep stage of the human subject, based on the number of respiration intervals that deviate from the mean respiration interval by less than the threshold parameter.

### Claim 2 (depends on 1)

The system of claim 1, wherein the system further comprises
a second sensor configured to detect a signal indicative of a heart rate of the human subject; and wherein
the controller is further configured to receive one or more signals from the second sensor, indicative of the heart rate of the human subject, and to
determine a heart rate of the human subject,
determine a change in heart rate of the human subject over a period of time, and
determine a level of wakefulness and/or sleep stage of the human subject based on both the number of respiration intervals that deviate from the mean respiration interval by less than the threshold parameter and the change in heart rate of the human subject over a period of time.

### Claim 3 (depends on 1)

The system of claim 1, wherein the first sensor comprises at least one sensor configured to detect a signal indicative of respiration effort comprises an inertial measurement unit (“IMU”), a microphone, a pressure sensor, a photoplethysmogram (“PPG”) sensor, and/or an electrocardiogram (“EKG”) sensor.

### Claim 4 (depends on 2)

The system of claim 2, wherein the second sensor comprises an IMU, a pressure sensor, a PPG sensor, and/or an EKG sensor; optionally wherein the second sensor is configured to detect both respiration and heart rate of the human subject.

### Claim 5 (depends on 4)

The system of claim 4, wherein the second sensor comprises a triaxial accelerometer and a gyroscope.

### Claim 6 (depends on 1)

The system of claim 1, wherein:
a) the first sensor is positioned on the chest and/or chin of the human subject;
b) the second sensor is a chest-worn IMU; and/or
c) the first sensor and/or the second sensor is an implantable sensor.

### Claim 7 (depends on 1)

The system of claim 1, wherein the threshold parameter is about or exactly ±0.1 seconds from the mean respiration interval.

### Claim 8 (depends on 1)

The system of claim 1, wherein the threshold parameter is about or exactly ±0.080, ±0.085, ±0.090, ±0.095, ±0.100, ±0.105, ±0.110, ±0.115, or ±0.120 seconds from the mean respiration interval.

### Claim 9 (depends on 1)

The system of claim 1, wherein the threshold parameter is about or exactly ±1.0%, ±1.5%, ±2.0%, ±2.5%, ±3.0%, ±3.5%, ±4.0%, ±4.5%, or ±5.0% from the mean respiration interval.

### Claim 10 (depends on 1)

The system of claim 1, wherein the controller is further configured to determine the level of wakefulness and/or sleep stage of the human subject, based on a percentage of respiration intervals within the finite trailing window that deviate from the mean respiration interval by less than the threshold parameter.

### Claim 11 (depends on 1)

The system of claim 1, wherein the controller is further configured to identify respiration intervals by:
a) identifying any unique point on two or more consecutive periods of a respiration waveform generated from the received one or more signals from the first sensor;
b) identifying consecutive peaks of a respiration waveform generated from the received one or more signals from the first sensor, and measure the time between these peaks; and/or
c) identifying consecutive troughs of a respiration waveform generated from the received one or more signals from the first sensor, and measure the time between these troughs; and/or
d) identifying any unique point on two or more consecutive periods of a respiration waveform generated from the received one or more signals from the first sensor; and/or
e) identifying consecutive points of maximum or minimum rates of change of a respiration waveform generated from the received one or more signals from the first sensor, and measure the time between these points.

### Claim 12 (depends on 1)

The system of claim 1, wherein the controller is further configured to identify respiration intervals by:
removing one or more low-frequency components of a respiration waveform generated from the received one or more signals from the first sensor, optionally wherein the low-frequency components comprise signals below 0.1 Hz; and
measuring the time between two consecutive positive or negative zero crossings.

### Claim 13 (depends on 1)

The system of claim 1, wherein the level of wakefulness and/or sleep stage of the human subject comprises a determination that the human subject is awake, in light sleep, in deep sleep, in REM sleep, or in an N1, N2, or N3 sleep stage.

### Claim 14 (depends on 1)

The system of claim 1, wherein the threshold parameter is based on a sleep study for the human subject.

### Claim 15 (depends on 1)

The system of claim 1, wherein the controller is further configured to modify the threshold parameter based on:
a) a physical orientation of the human subject; and/or
b) a mean respiration interval for a prior finite trailing window.

### Claim 16 (depends on 2)

The system of claim 2, wherein the controller is further configured to
determine the change in heart rate of the human subject over a period of time based on a past mean heart rate value for the human subject.

### Claim 17 (depends on 1)

A system for treating obstructive sleep apnea, comprising:
the computer-implemented system for determining a level of wakefulness and/or sleep stage of a human subject, of claim 1, and
a stimulation system, communicatively linked to the controller and configured to deliver stimulation to a nerve which innervates an upper airway muscle of the human subject based on the level of wakefulness and/or sleep stage of the human subject determined by the controller.

### Claim 18 (depends on 17)

The system of claim 17, wherein the controller is configured to cause the stimulation system to apply, increase, decrease, temporarily pause, or terminate the stimulation based on the level of wakefulness and/or sleep stage of the human subject.

### Claim 19 (depends on 17)

The system of claim 17, wherein the controller is configured to cause the stimulation system to change an amplitude, pulse width, duty cycle, stimulation duration, and/or frequency of the stimulation based on the level of wakefulness and/or sleep stage of the human subject.

### Claim 20

A method for determining a level of wakefulness and/or sleep stage of a human subject, comprising:
a) detecting a signal indicative of respiration effort by the human subject, using a first sensor placed on or in proximity to one or more regions of a chest and/or head of the human subject;
b) transmitting the detected signal to a controller communicatively linked to the first sensor and configured to receive the signal from the first sensor indicative of respiration effort by the human subject;
c) determining, by the controller, a mean respiration interval for a finite trailing window, using the received signal;
d) determining, by the controller, a number of respiration intervals within the finite trailing window that deviate from the mean respiration interval by less than a threshold parameter; and
e) determining, by the controller, a level of wakefulness and/or sleep stage of the human subject, based on the number of respiration intervals that deviate from the mean respiration interval by less than the threshold parameter.

### Claim 21 (depends on 20)

The method of claim 20, further comprising:
f) applying, increasing, decreasing, temporarily pausing, or terminating stimulation of at least one nerve which innervates an upper airway muscle of the human subject, using a stimulation system communicatively linked to the controller, based on the level of wakefulness and/or sleep stage of the human subject determined by the controller.

### Claim 22 (depends on 21)

The method of claim 21, where step f) further comprises changing an amplitude, pulse width, duty cycle, stimulation duration, and/or frequency of the stimulation based on the level of wakefulness and/or sleep stage of the human subject.