AC/DC multi-axis accelerometer for determining patient activity and body position

• US 6,466,821 B1
• Filed: 12/08/1999
• Issued: 10/15/2002
• Est. Priority Date: 12/08/1999
• Status: Expired due to Fees

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Florio, Joseph J., Bornzin, Gene A., Park, Euljoon, Vogel, Alan B., Pianca, Anne M., Mandell, Lee Jay, Mai, Junyu
• Primary Examiner(s): EVANISKO, GEORGE ROBERT
• Application Number:
  US09/457,451
• Time in Patent Office: 1,042 Days
• Field of Search: 607/17-19, 600/595
• US Class Current: 607/18
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration

Abstract

An implantable cardiac stimulation device which determines stimulation based upon the patient'"'"'s body position and activity level while eliminating special implantation or calibration procedures. To eliminate such special implantation and calibration procedures, the stimulation device correlates the patient'"'"'s body position using a multi-axis DC accelerometer or other sensor during times of high activity and determines a patient'"'"'s standing position value. During other times, the stimulation device compares the signals from the accelerometer to the standing position value to determine the patient'"'"'s current body position. Based upon the current body position and the activity level, the stimulation device determines the necessary stimulation to deliver to the patient.

Claims

1. An implantable cardiac stimulation device for stimulating a patient'"'"'s heart based upon a determination of the patient'"'"'s body position and activity level, the stimulation device comprising:

a pulse generator configured to generate stimulation pulses at a controlled stimulation rate;

a first sensor positioned along a first sensor axis and configured to deliver a first signal having a DC position signal component indicative of the position of the patient'"'"'s body along the first sensor axis and an AC activity level component indicative of activity of the patient'"'"'s body along the first sensor axis;

a second sensor positioned along a second sensor axis, essentially orthogonal to the first sensor axis, and configured to deliver a second signal having a DC position signal component indicative of the position of the patient'"'"'s body along the second sensor axis and an AC activity level component indicative of activity of the patient'"'"'s body along the second sensor axis;

a controller, connected to the pulse generator and the first and second sensors, that triggers the pulse generator to generate stimulation pulses in response to activity level signals and a patient'"'"'s calculated body position; and

wherein

the controller periodically calculates the patient'"'"'s body position as a function of the activity level and position signals.

2. The stimulation device of claim 1 wherein the patient'"'"'s body position is defined by at least a first and second body axis which need not coincide with the axes defined by the first and second sensor axes.

3. The stimulation device of claim 1 wherein the controller determines whether the patient is standing by processing the activity level and the position signals.

4. The stimulation device of claim 1 wherein the controller periodically correlates the position signals from the first and second sensors to a determined standing position to determine whether the patient'"'"'s current body position corresponds to the standing position.

5. The stimulation device of claim 4 wherein the controller correlates the position signals designated as (x, y) to the determined standing position designated as (x_c, y_c) via a projection value (P) according to an equation:

$P=\frac{\left(x*x_c+y*y_c\right)}{\left(x_c^2+y_c^2\right)}$

where x is the position signal from a first sensor, y is the position signal from the second sensor, x_c is an average over a time period of the position signals from the first sensor when the patient'"'"'s sensed activity is greater than an activity threshold level, and y_c is an average over the time period of the position signals from the second sensor when the patient'"'"'s sensed activity is greater than the activity threshold level.

6. The stimulation device of claim 5 wherein the controller determines that the position signals indicate that the patient is standing when the projection value (P) is greater than a predetermined projection threshold value and the patient is not standing when the projection value (P) is less than the predetermined projection threshold value.

7. The stimulation device of claim 6 wherein the predetermined threshold value is greater than 0.65.

8. The stimulation device of claim 1 wherein the first and second sensors are accelerometers.

9. The stimulation device of claim 1 additionally comprising a third sensor positioned along a third sensor axis, essentially orthogonal to at least the first or the second sensor axis, and in communication with the controller to deliver a third signal having a DC position signal component indicative of the position of the patient'"'"'s body along the third axis and additionally configured to deliver an AC activity level component indicative of activity of the patient'"'"'s body along the third sensor axis.

10. The stimulation device of claim 9 wherein the controller correlates the position signals designated as (x, y, z) to a determined standing orientation designated as (x_c, y_c, z_c) via a projection value (P) according to an equation:

$P=\frac{\left(x*x_c+y*y_c+z*z_c\right)}{\left(x_c^2+y_c^2+z_c^2\right)}$

wherein x is the position signal from a first sensor, y is the position signal from the second sensor, z is a position signal from the third sensor, x_c is an average over a time period of the position signals from the first sensor when the patient'"'"'s sensed activity is greater than an activity threshold level, y_c, is an average over the time period of the position signals from the second sensor when the patient'"'"'s sensed activity is greater than the activity threshold level and z_c is an average over the time period of the position signals from the third sensor when the patient'"'"'s sensed activity is greater than the activity threshold level.

11. The stimulation device of claim 1 wherein:

the controller determines the stimulation rate based upon at least one of three stimulation regimes comprising at least one of;

activity indicated rate, circadian base rate, and orthostatic compensation rate, wherein the activity indicated rate is determined based upon the patient'"'"'s sensed activity level, the circadian base rate is determined based upon the patient'"'"'s sensed activity level and a history of the patient'"'"'s sensed activity level, and the orthostatic compensation rate is based upon a predetermined stimulation pattern; and

wherein

the controller determines which stimulation regime to use based upon the patient'"'"'s sensed activity level and the patient'"'"'s sensed body position.

12. The stimulation device of claim 11, wherein the controller determines the stimulation rate to be a maximum of the activity indicated rate and the circadian base rate when there is no sensed change in body position.

13. The stimulation device of claim 11, wherein the controller determines the stimulation rate to be a maximum of the activity indicated rate, the circadian base rate, and the orthostatic compensation rate when there is a sensed change of the patient'"'"'s body position from not standing to standing.

14. The stimulation device of claim 11 wherein the controller determines the stimulation rate to be a maximum of the activity indicated rate and the circadian base rate when the body position has changed from standing to not standing.

15. The stimulation device of claim 1 wherein:

the controller calculates a standing position value for the patient as a function of the activity level and position signals; and

wherein

the controller determines the presence of twiddler'"'"'s syndrome by monitoring changes in the calculated standing position value.

16. A cardiac stimulation device, implantable within a patient'"'"'s body for stimulating a patient'"'"'s cardiac tissue at a cardiac stimulation rate, the stimulation device comprising:

detection means for detecting first signals for indicating patient activity level and second signals for indicating orientation of the patient'"'"'s body;

means for determining a standing position based on the patient'"'"'s activity level signals and body position signals;

pulse means for generating stimulation pulses;

control means, connected to the detection means and the pulse means, for determining the stimulation rate based upon the detection means and for triggering the pulse means in response thereto; and

wherein

the control means determines the stimulation rate based upon a current activity signal level and a current body position signal relative to the determined standing position.

17. The stimulation device of claim 16 wherein:

the control means further comprises means for determining a change in body position, and

the control means determines the stimulation rate based upon the patient activity level, the patient body position, and changes in body position.

18. The stimulation device of claim 16 wherein:

the control means further comprises means for determining a time between changes in patient body position; and

the control means determines the stimulation rate based upon the patient activity level, the patient body position, the change in body position, and the time between changes in patient body position.

19. The stimulation device of claim 16 wherein the means for calculating a standing position comprises determining when the patient'"'"'s activity level exceeds a standing threshold and designating the patient'"'"'s body position as the standing position when the patient'"'"'s activity level exceeds the standing threshold.

20. The stimulation device of claim 19 wherein the standing threshold corresponds to a patient'"'"'s activity level which indicates that the patient is exercising.

21. The stimulation device of claim 16 wherein the detection means correlates the second signals to the calculated standing position via an equation:

$P=\frac{\left(x*x_c+y*y_c\right)}{\left(x_c^2+y_c^2\right)}$

where x is the position signal from a first of at least two accelerometers, y is the position signal from a second of the at least two accelerometers, x_c is an average over a time period of the position signals from the first accelerometers when the patient'"'"'s activity is greater than the activity level, and y_c is an average over a time period of the position signals from the second accelerometers when the patient'"'"'s activity is greater than the activity level.

22. The stimulation device of claim 21 wherein the detection means determines that the patient is standing when the projection value (P) is greater than a predetermined threshold and that the patient is not standing when the projection value (P) is less than the predetermined threshold.

23. The stimulation device of claim 16 wherein:

the control means further comprises means for determining a stimulation regime based upon the patient'"'"'s activity level and the patient'"'"'s body position, wherein the stimulation regime comprises at least one of;

an activity indicated rate, a circadian base rate, and an orthostatic compensation rate; and

wherein the activity indicated rate is determined based upon the patient activity level, the circadian base rate is determined based upon the patient activity level and a history of the patient activity level, and the orthostatic compensation rate is based upon a predetermined stimulation pattern.

25. The stimulation device of claim 23 wherein the means for determining a stimulation regime sets the stimulation rate to be a maximum of the activity indicated rate and the circadian base rate when the body position has changed from standing to not standing.

26. The stimulation device of claim 23 wherein the means for determining a stimulation regime sets the stimulation rate to be a maximum of the activity indicated rate, the circadian base rate, and the orthostatic compensation rate when the body position has changed from not standing to standing.

27. The stimulation device of claim 16 further comprising means for determining the presence of twiddler'"'"'s syndrome by monitoring for changes in the calculated standing position.

24. The stimulation device of 23 wherein the means for determining a stimulation regime sets the stimulation rate to be a maximum of the activity indicated rate and the circadian base rate when there is no change in the patient'"'"'s body position.

28. A method of stimulating a patient'"'"'s heart with a cardiac stimulator implantable within a patient'"'"'s body, wherein the implantable stimulator comprises a pulse generator for triggering stimulation pulses in response to a sensor for sensing activity and position information along at least two essentially orthogonal axes for generating responsive signals, the method comprising:

generating signals indicating the activity of the patient'"'"'s body;

generating signals indicating the relative position of the patient'"'"'s body;

processing the activity and position signals to determine a standing position for the patient;

periodically processing the activity and position signals with reference to the determined standing position to determine whether the patient is standing; and

determining a stimulation rate for stimulating the patients heart based upon a current patient activity level and a current patient position, relative to the determined standing position.

29. The method of claim 28 wherein the step of determining of the patient standing position comprises:

processing the patient activity level signal over a period of time to determine a patient activity variance;

monitoring the patient activity level and the patient activity variance to determine when the patient activity level exceeds an activity standing threshold and the patient activity variance exceed an activity variance standing threshold; and

when the patient activity level exceeds the activity standing threshold and the patient activity variance exceed the activity variance standing threshold, processing the position signals to determine the patient standing position having at least two dimensions (x_c, y_c), where x_c is an average over a time period of position signals from a first sensor when the patient'"'"'s sensed activity is greater than an activity threshold level, and y_c is an average over the time period of position signals from a second sensor when the patient'"'"'s sensed activity is greater than the activity threshold level.

30. The method of claim 29 wherein the step of processing to determine whether the patient is standing comprises correlating the current position signals (x, y) to (x_c, y_c), where x is the position signal from the first sensor, and y is the position signal from the second sensor.

31. The method of claim 30 wherein the step of correlating the position signals comprises:

calculating a projection value (P), according to an equation;

$P=\frac{\left(x*x_c+y*y_c\right)}{\left(x_c^2+y_c^2\right)}$

wherein the patient position is determined to be standing if the projection value (P) is greater than a predetermined threshold and the patient position is determined to be not standing if the projection value (P) is less than the predetermined threshold.

32. The method of claim 31 wherein the step of determining a stimulation rate comprises:

monitoring the patient position over time as a last patient position and a current patient position; and

determining the stimulation rate based upon the patient activity level, the patient activity variance, the last patient position, and the current patient position.

33. The method of claim 32 wherein the step of determining the stimulation rate further comprises:

deriving the stimulation rate from one of three stimulation regimes comprising at least one of;

an activity indicated rate, a circadian base rate, and an orthostatic compensation rate based upon the patient activity level, the patient activity variance, the last patient position, and the current patient position; and

wherein the activity indicated rate is determined based upon the patient activity level, the circadian base rate is determined based upon the patient activity level and a history of the patient'"'"'s activity level, and the orthostatic compensation rate is based upon a predetermined stimulation pattern.

34. The method of claim 33 wherein the step of determining the stimulation rate further comprises determining the stimulation rate to be a maximum of the activity indicated rate and the circadian base rate based upon the patient activity level and the patient activity variance when the last patient position and the current patient position are the same.

35. The method of claim 33 wherein the step of determining the stimulation rate further comprises determining the stimulation rate to be a maximum of the activity indicated rate, the circadian base rate, and the orthostatic compensation rate based upon the patient activity level, the patient activity variance, and a time pointer when the last patient position is not standing and the current patient position is standing.

36. The method of claim 33 wherein the step of determining the stimulation rate further comprises determining the stimulation rate to be a maximum of the activity indicated rate, the circadian base rate when the last patient position is standing and the current patient position is not standing.

37. The method of claim 28 wherein the step of processing the activity and position signals to determine a standing position for the patient further includes monitoring changes in the determined standing position to determine the existence of twiddler'"'"'s syndrome.