Posture detector calibration and use

• US 20070118056A1
• Filed: 11/18/2005
• Published: 05/24/2007
• Est. Priority Date: 11/18/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Wang, Hua, Hatlestad, John
• Granted Patent: US 8,366,641 B2
• Time in Patent Office: Days
• US Class Current: 600/595
• CPC Class Codes: A61B 2562/0219 Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches
• CPC Class Codes: A61B 5/1116 Determining posture transitions
• CPC Class Codes: A61B 5/1117 Fall detection
• CPC Class Codes: A61B 5/686 Permanently implanted devices, e.g. pacemakers, other stimulators, biochips A61B5/6861 takes precedence

Abstract

Calibrating a posture detector for a patient'"'"'s body involves measuring outputs of one or more sensors disposed in relation to the patient'"'"'s body while the patient assumes a plurality of positions. A transfer matrix is formed having coefficients corresponding to the measured outputs. The transfer matrix defines a relationship between a coordinate system of the one or more sensors and a coordinate system of the patient'"'"'s body. The body coordinate system is used as a reference coordinate system for posture detection. Posture, including tilt and/or tilt angle, may be determined based on first and second rotational angles defined in relation to the body coordinate system.

Claims

1. A posture sensing method, comprising:

measuring outputs of one or more sensors disposed in relation to a patient'"'"'s body while the patient assumes a plurality of body postures, the one or more sensors responsive to a gravitational field;

forming a transfer matrix, the transfer matrix having coefficients corresponding to the measured outputs and defining a relationship between a coordinate system of the one or more sensors and a coordinate system of the patient'"'"'s body; and

determining a posture of the patient'"'"'s body using the body coordinate system as a reference coordinate system.

2. The method of claim 1, wherein the coefficients comprise the measured outputs divided by a magnitude of the gravitational field.

3. The method of claim 1, wherein measuring the outputs of the one or more sensors comprises measuring the outputs of one or more accelerometers.

4. The method of claim 3, wherein sensitive axes of at least two accelerometers are oriented substantially orthogonally.

5. The method of claim 1, wherein measuring the outputs of the one or more sensors comprises measuring the outputs of the one or more sensors while the patient assumes two or more substantially mutually orthogonal body postures.

6. The method of claim 1, wherein measuring the outputs of the one or more sensors while the patient assumes the plurality of body postures comprises:

measuring the outputs of the one or more sensors while the patient is upright or upside down;

measuring the outputs of the one or more sensors while the patient is lying on a right side or lying on a left side; and

measuring the outputs of the one or more sensors while the patient is prone or supine.

7. The method of claim 1, wherein at least one of measuring the outputs of the one or more sensors, forming the transfer matrix, and determining the posture of the patient'"'"'s body is performed at least in part implantably.

8. The method of claim 1, wherein determining the posture of the patient'"'"'s body comprises determining tilt of the patient'"'"'s body.

9. The method of claim 1, wherein determining the posture of the patient'"'"'s body comprises determining a tilt angle of the patient'"'"'s body.

10. The method of claim 9, wherein determining the tilt angle comprises determining the tilt angle to within about five degrees with respect to a plane.

11. The method of claim 1, wherein determining the posture of the patient'"'"'s body comprises:

determining first and second rotational angles associated with posture;

comparing the first and the second rotational angles to threshold values; and

determining the posture based on the comparisons.

12. A posture detector, comprising:

one or more sensors responsive to a gravitational field, each sensor disposed in relation to a patient'"'"'s body and configured to output a signal based on an orientation of the patient;

calibration circuitry coupled to the one or more sensors and configured to form a transfer matrix having coefficients corresponding to the sensor outputs, the transfer matrix defining a relationship between a coordinate system of the one or more sensors and a coordinate system of the patient'"'"'s body; and

a posture processor coupled to the one or more sensors and the calibration circuitry and configured to determine a posture of the patient'"'"'s body using the body coordinate system as a reference coordinate system.

13. The posture detector of claim 12, wherein coefficients of the transfer matrix comprise the sensor outputs divided by a magnitude of the gravitational field.

14. The posture detector of claim 12, wherein sensitive axes of the one or more sensors are oriented substantially orthogonally.

15. The posture detector of claim 12, wherein at least one of the one or more sensors, the calibration circuitry, and the posture processor comprise an implantable component.

16. The posture detector of claim 12, wherein the one or more sensors comprise one or more accelerometers.

17. The posture detector of claim 12, wherein the posture processor is configured to determine a tilt of the patient'"'"'s body.

18. The posture detector of claim 12, wherein the posture processor is configured to determine a tilt angle of the patient'"'"'s body.

19. The posture detector of claim 12, further comprising a diagnostics processor configured to determine a presence cardiac decompensation based on the tilt angle.

20. The posture detector of claim 12, wherein the diagnostics processor is configured to track progression of disease based on changes in the tilt angle.

21. A posture sensing system, comprising:

means for measuring outputs of one or more sensors responsive to a gravitational field disposed in relation to a patient'"'"'s body while the patient assumes a plurality of body postures;

means for forming a transfer matrix having coefficients corresponding to the measured outputs, the transfer matrix defining a relationship between a coordinate system of the one or more sensors and a coordinate system of the patient'"'"'s body; and

means for determining a posture of the patient'"'"'s body using the body coordinate system at a reference coordinate system.

22. The system of claim 21, further comprising means for determining a tilt angle of the patient'"'"'s body.

23. A posture sensing method, comprising:

determining first and second rotational angles associated with posture;

comparing the first and the second rotational angles to threshold values; and

determining the posture based on the comparisons.

24. The method of claim 23, wherein:

determining the first rotational angle comprises determining a polar angle with respect to a first axis of a body coordinate system; and

determining the second rotational angle comprises determining an azimuthal angle within a plane of the second and third axes of the body coordinate system.

25. The method of claim 24, wherein the first axis of the body coordinate system is oriented substantially along the inferior-superior axis of the patient'"'"'s body.

26. The method of claim 24, wherein the first, second and third axes are substantially mutually orthogonal, and one of the second or third axes is oriented substantially along the anterior-posterior axis of the patient'"'"'s body.

27. The method of claim 23, wherein determining the first and the second rotational angles comprises:

defining a vector associated with the posture;

determining the posture based on an orientation of the vector with respect to a body coordinate system.

28. The method of claim 23, wherein determining the posture of the patient'"'"'s body comprises determining tilt of the patient'"'"'s body.

29. The method of claim 23, wherein determining the posture of the patient'"'"'s body comprises determining a tilt angle of the patient'"'"'s body.

30. A posture detector, comprising:

one or more sensors responsive to a gravitational field disposed in relation to a patient'"'"'s body, each sensor configured to output a signal based on an orientation of the patient; and

a posture processor coupled to the one or more sensors and configured to determine first and second rotational angles associated with the posture from the sensor outputs and to determine the posture based on the first and second rotational angles.

31. The posture detector of claim 30, wherein the one or more sensors comprise one or more accelerometers.

32. The posture detector of claim 30, wherein the posture processor is configured to compare the first and the second rotational angles to threshold values and to determine the posture based on the comparisons.

33. The posture detector of claim 30, wherein:

the first rotational angle comprises a polar angle with respect to a first axis of a body coordinate system; and

the second rotational angle comprises an azimuthal angle within a plane of the second and third axes of the body coordinate system.

34. The posture detector of claim 33, wherein the first axis of the body coordinate system is oriented substantially along the inferior-superior axis of the patient'"'"'s body.

35. The posture detector of claim 33, wherein the first, second and third axes are substantially mutually orthogonal, and one of the second or third axes is oriented substantially along the anterior-posterior axis of the patient'"'"'s body.

36. The posture detector of claim 30, wherein the posture processor is configured to define a vector associated with the posture and to determine the posture based on an orientation of the vector with respect to a body coordinate system.

37. The posture detector of claim 30, wherein the posture processor is configured to determine a tilt angle of the patient'"'"'s body.

38. A posture sensing system, comprising:

means for determining first and second rotational angles associated with posture;

means for comparing the first and the second rotational angles to threshold values; and

means for determining the posture based on the comparisons.

39. The system of claim 38, further comprising:

means for determining a polar angle with respect to a first axis of a body coordinate system; and

means for determining an azimuthal angle within a plane of the second and third axes of the body coordinate system.

40. The system of claim 38, wherein the first axis of the body coordinate system is oriented substantially along the inferior-superior axis of the patient'"'"'s body.

41. The system of claim 38, wherein the first, second and third axes are substantially mutually orthogonal, and one of the second or third axes is oriented substantially along the anterior-posterior axis of the patient'"'"'s body.

42. The system of claim 38, further comprising:

means for defining a vector associated with the posture; and

means for determining the posture based on an orientation of the vector with respect to a body coordinate system.

43. The system of claim 38, further comprising means for determining a tilt angle of the patient'"'"'s body.