POSTURE SENSOR AUTOMATIC CALIBRATION

• US 20130298636A1
• Filed: 07/18/2013
• Published: 11/14/2013
• Est. Priority Date: 06/12/2008
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Hatlestad, John D., Lewicke, Aaron, Maile, Keith R.
• Granted Patent: US 9,523,706 B2
• Time in Patent Office: Days
• US Class Current: 73/1.38
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/103 Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes A61B5/08 takes precedence; measuring aids for tailors A41H1/00; measuring instruments specially adapted for dentistry A61C19/04
• CPC Class Codes: A61B 5/1038 Measuring plantar pressure during gait
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence
• CPC Class Codes: G01C 22/00 Measuring distance traversed on the ground by vehicles, persons, animals or other moving solid bodies, e.g. using odometers, using pedometers
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38
• CPC Class Codes: G01D 18/00 Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
• CPC Class Codes: G01P 13/00 Indicating or recording presence, absence, or direction, of movement electric switches H01H; counting moving objects G06M7/00
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups
• CPC Class Codes: G06F 17/40 Data acquisition and logging for input to computer G06F3/00
• CPC Class Codes: G16H 20/30 relating to physical therapies or activities, e.g. physiotherapy, acupressure or exercising
• CPC Class Codes: G16H 40/67 for remote operation
• CPC Class Codes: G16Z 99/00 Subject matter not provided for in other main groups of this subclass

Abstract

A system and method automatically calibrate a posture sensor, such as by detecting a walking state or a posture change. For example, a three-axis accelerometer can be used to detect a patient'"'"'s activity or posture. This information can be used to automatically calibrate subsequent posture or acceleration data.

Claims

1. A device comprising:

an accelerometer configured to sense an acceleration signal from a patient;

a filter circuit configured to extract a characteristic of the acceleration signal;

a comparison circuit configured to perform a comparison between the characteristic of the acceleration signal and a stored template to distinguish a first state of the patient from a second state of the patient; and

a posture calibration circuit configured to use an orientation of the accelerometer in the first state to perform a posture calibration of the acceleration signal of the accelerometer.

2. The device of claim 1, wherein the filter circuit includes a highpass filter circuit configured to extract an AC component of the acceleration signal, the characteristic of the acceleration signal including a characteristic of the AC component of the acceleration signal.

3. The device of claim 1, wherein the filter circuit includes a lowpass filter circuit configured to extract a DC component of the acceleration signal.

4. The device of claim 3, comprising a signal processor circuit configured to:

determine a gravity vector using the DC component of the acceleration signal;

compute a parallel component of the acceleration signal, the parallel component being in the direction of the gravity vector;

compute an orthogonal component of the acceleration signal, the orthogonal component being in a direction orthogonal to the gravity vector;

compare the parallel component to a parallel template and compare the orthogonal component to an orthogonal template; and

distinguish the first state from the second state using the computed parallel component of the acceleration signal and using the computed orthogonal component of the acceleration signal.

5. The device of claim 4, wherein the signal processor circuit configured to distinguish the first state from the second state includes:

determining a central tendency of the gravity vectors;

comparing the central tendency of the gravity vectors to a previously-determined central tendency of the gravity vectors; and

determining whether the gravity vectors are consistent using a difference between the central tendency of the gravity vectors and the previously-determined central tendency of the gravity vectors.

6. The device of claim 1, wherein the stored template includes a stored domain template, the domain being at least one of frequency, time, and time-frequency.

7. The device of claim 6, wherein the comparison circuit is configured to perform a comparison between the characteristic and the stored domain template, wherein the characteristic comprises a domain characteristic.

8. The device of claim 1, comprising a communication circuit configured to:

receive posture calibration information from the posture calibration circuit; and

communicate the posture calibration information to an external local interface.

9. A device comprising:

an accelerometer configured to sense an acceleration signal from a patient;

a first filter circuit configured to extract a first component of the acceleration signal;

a comparison circuit configured to perform a comparison between a characteristic of the first component of the acceleration signal and a stored template to distinguish a first state of the patient from a second state of the patient;

a second filter circuit configured to extract a second component of the acceleration signal;

a signal processor circuit configured to;

determine a gravity vector using the second component of the acceleration signal;

compute a parallel component of the acceleration signal, the parallel component being in the direction of the gravity vector;

compute an orthogonal component of the acceleration signal, the orthogonal component being in a direction orthogonal to the gravity vector;

compare the parallel component to a parallel template and compare the orthogonal component to an orthogonal template; and

distinguish the first state from the second state using the computed parallel component of the acceleration signal and using the computed orthogonal component of the acceleration signal; and

a posture calibration circuit configured to use an orientation of the accelerometer in the first state to perform a posture calibration of the acceleration signal of the accelerometer.

10. The device of claim 9, wherein the first filter circuit includes a highpass filter circuit, the first component including an AC component of the acceleration signal.

11. The device of claim 9, wherein the second filter circuit includes a lowpass filter circuit, the second component including a DC component of the acceleration signal.

12. The device of claim 9, wherein the signal processor circuit configured to distinguish the first state from the second state includes:

determining a central tendency of the gravity vectors;

comparing the central tendency of the gravity vectors to a previously-determined central tendency of the gravity vectors; and

determining whether the gravity vectors are consistent using a difference between the central tendency of the gravity vectors and the previously-determined central tendency of the gravity vectors.

13. The device of claim 9, comprising a communication circuit configured to:

receive posture calibration information from the posture calibration circuit; and

communicate the posture calibration information to an external local interface.

14. A method comprising:

sensing an acceleration signal from a patient using an accelerometer;

detecting a first state using the acceleration signal, the detecting the first state including;

extracting a characteristic of an AC component of the acceleration signal;

performing a comparison between the characteristic and a template; and

using the comparison to distinguish the first state from a second state; and

using an orientation of the accelerometer in the first state to perform a posture calibration of the acceleration signal of the accelerometer.

15. The method of claim 14, comprising:

computing a DC component of the acceleration signal;

determining a gravity vector using the DC component of the acceleration signal;

computing a parallel component of the acceleration signal, the parallel component being in the direction of the gravity vector;

computing an orthogonal component of the acceleration signal, the orthogonal component being in a direction orthogonal to the gravity vector;

wherein the performing the comparison comprises comparing the parallel component to a parallel template and comparing the orthogonal component to an orthogonal template; and

wherein the using the comparison to distinguish the first state from the second state comprises using the computed parallel component of the acceleration signal and using the computed orthogonal component of the acceleration signal.

16. The method of claim 15, wherein the using the comparison to distinguish the first state from the second state comprises comparing the parallel comparison to a first threshold value and comparing the orthogonal comparison to a second threshold value.

17. The method of claim 15, wherein:

computing the DC component of the acceleration signal comprises computing a DC component of the acceleration signal in each of orthogonal x, y, and z directions of the accelerometer; and

determining a gravity vector comprises determining a three dimensional gravity vector using the DC component of the acceleration signal in each of x, y, and z directions of the accelerometer.

18. The method of claim 15, wherein using the comparison to distinguish the first state from the second state comprises:

determining a central tendency of the gravity vectors;

comparing the central tendency of the gravity vectors to a previously-determined central tendency of the gravity vectors; and

determining whether the gravity vectors are consistent using a difference between the central tendency of the gravity vectors and the previously-determined central tendency of the gravity vectors.

19. The method of claim 14, wherein performing a comparison between the characteristic and a template comprises performing the comparison between at least one of:

a frequency-domain characteristic and a frequency-domain template;

a time-domain characteristic and a time-domain template; and

a time-frequency-domain characteristic and a time-frequency-domain template.

20. The method of claim 14, wherein extracting an AC component of the acceleration signal comprises extracting the AC component with a highpass filter.