Magnetoresistive-based position sensor for use in an implantable electrical device

• US 6,430,440 B1
• Filed: 12/08/1999
• Issued: 08/06/2002
• 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: Gibson, Scott, Vogel, Alan B., Shankar, Balakrishnan, McNeil, Kenneth R. II
• Primary Examiner(s): Jastrzab, Jeffrey F.
• Assistant Examiner(s): Oropeza, Frances P.
• Application Number:
  US09/457,194
• Time in Patent Office: 972 Days
• Field of Search: 600/595, 607/4, 607/5, 607/7, 607/9, 607/11, 607/17, 607/19
• US Class Current: 607/19
• CPC Class Codes: A61B 5/11 Measuring movement of the entire body or parts thereof, e.g. head or hand tremor, mobility of a limb for measuring pulse A61B5/02 ;A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration

Abstract

An implantable cardiac stimulation device including an activity/position sensor that incorporates a magnetoresistive sensor and a magnet that are positioned so as to move relative to each other in response to activity and the body position of the patient when the device is implanted in the body of the patient. In one embodiment, the sensor includes a magnetoresistive sensor that is made from giant magnetoresistive (GMR) materials. Preferably, a magnet is positioned on a flexible cantilevered beam so as to be positioned adjacent the magnetoresistive sensor. Movement of the patient results in relative movement of the magnet with respect to the magnetoresistive sensor and generates a signal having an AC component corresponding to a patient'"'"'s activity and a DC component corresponding to the patient'"'"'s body position. The signal can be used by the implantable cardiac stimulation device'"'"'s processor for adjusting the delivery of therapeutic electrical stimulation such as by adjusting the pacing rate of pacing pulses being delivered to the patient'"'"'s heart.

Claims

1. A magnetoresistive position sensor assembly suitable for use in a cardiac stimulation device implanted within a patient'"'"'s body to determine the position of the patient'"'"'s body, the sensor assembly comprising:

a substrate having a first and a second surface, the substrate being mounted within the cardiac stimulation device;

a magnet;

a magnetoresistive sensor that produces a variable position signal proportional to the relative positions of the magnet and the magnetoresistive sensor; and

means for mounting the magnetoresistive sensor and the magnet proximate to the first surface of the substrate and displaced from each other by a variable amount, the amount alterable in response to changes in the patient'"'"'s body position, wherein the variable position signal corresponds to the patient'"'"'s body position.

2. The sensor assembly of claim 1, wherein the mounting means comprises:

a flexible cantilevered beam having first and second ends, the first end of the cantilevered beam being attached to the first surface of the substrate;

the magnetoresistive sensor being mounted proximate to the second end of the cantilevered beam; and

the magnet being mounted to the first surface of the substrate so as to be positioned adjacent the magnetoresistive sensor.

3. The sensor assembly of claim 1, wherein the mounting means comprises:

a flexible cantilevered beam having first and second ends, the first end of the cantilevered beam being attached to the first surface of the substrate;

the magnet being mounted proximate to the second end of the cantilevered beam; and

the magnetoresistive sensor being mounted to the first surface of the substrate so as to be positioned adjacent the magnet.

4. The sensor assembly of claim 1, wherein the mounting means comprises:

the magnetoresistive sensor being mounted on the first surface of the substrate;

a mounting block that is positioned on the first surface of the substrate;

a flexible cantilevered beam, having an inner and an outer end, attached to the mounting block at the inner end so that the outer end of the flexible cantilevered beam extends outward from the mounting block; and

wherein

the magnet is mounted on the outer end of the flexible cantilevered beam so as to be positioned adjacent the magnetoresistive sensor.

5. The sensor assembly of claim 1, wherein the magnetoresistive sensor is formed out of giant magnetoresistive (GMR) materials.

6. The sensor assembly of claim 1, wherein the magnetoresistive sensor is comprised of a bridge circuit having at least one resistor formed out of giant magnetoresistive (GMR) materials, the bridge circuit producing an output voltage signal.

7. The sensor assembly of claim 6, further comprising an activity/position circuit that receives the output voltage signal from the bridge circuit and provides signals indicative of the body position and the activity level of the patient having the cardiac stimulation device mounted within.

8. The device of claim 7, wherein the activity level signal is indicative of both the frequency and magnitude of the relative motion of the magnet and the magnetoresistive sensor.

9. The device of claim 8, wherein the activity/position circuit includes:

a voltage controlled oscillator that receives the output voltage signal from the bridge circuit and oscillates at a frequency that is proportional to the magnitude of the output voltage signal;

a counter which receives an output signal of the voltage controlled oscillator and provides a digital signal indicative of the oscillations of the voltage controlled oscillator; and

wherein

the activity level signal corresponds to a periodic sample of the counter value.

10. An implantable cardiac stimulation device contained within a casing and adapted to be implanted in the body of a patient, the device comprising:

delivery means for delivering therapeutic electrical stimulation to the heart of the patient;

control means for controlling the delivery of therapeutic electrical stimulation to the heart of the patient;

an activity/position sensor incorporating a magnet and a magnetoresistive sensor, the activity/position sensor being adapted to be implanted in the body of the patient so that movement of the patient results in relative movement between the magnet and the magnetoresistive sensor so that the magnetoresistive sensor provides a variable position signal that is indicative of the body position of the patient; and

wherein

the control means controls the delivery of therapeutic electrical stimulation to the heart of the patient responsive, at least in part, to the variable position signal.

11. The device of claim 10, wherein the delivery means comprises at least one lead that is adapted to be positioned adjacent to the wall of the heart and is further adapted to deliver pacing pulses to the heart.

12. The device of claim 11, wherein the control means comprises a processor that is positioned within the casing, wherein the processor is adapted to receive the variable position signal and to use the variable position signal to adjust the frequency of the pacing pulses that are to be delivered to the heart via the at least one lead.

13. The device of claim 10, wherein the control means is adapted to adjust the pacing rate in response to variations in the variable position signal, wherein the variations in the variable position signal are indicative of a patient'"'"'s activity level.

14. The device of claim 10, wherein the activity/position sensor additionally comprises:

a substrate having a first and a second surface that is positioned within the casing of the implantable cardiac stimulation device wherein the magnetoresistive sensor is mounted on the substrate; and

wherein

the magnet is movably mounted proximate to the substrate so that when the casing is implanted in the body of a patient, activity of the patient results in the magnet moving with respect to the magnetoresistive sensor so that the magnetoresistive sensor produces the variable position signal that is proportional to the movement of the magnet with respect to the magnetoresistive sensor.

15. The device of claim 14, wherein the activity/position sensor further comprises:

a mounting block that is positioned on the first surface of the substrate;

a flexible cantilevered beam that is attached to the mounting block so that the flexible cantilevered beam extends outward from the mounting block; and

wherein

the magnet is mounted on the outer end of the flexible cantilevered beam so as to be positioned adjacent the magnetoresistive sensor.

16. The device of claim 10, wherein the magnetoresistive sensor is formed out of giant magnetoresistive (GMR) materials.

17. The device of claim 10, wherein the magnetoresistive sensor is comprised of a bridge circuit having at least one resistor formed out of giant magnetoresistive (GMR) materials.

18. The device of claim 17, further comprising an activity/position circuit that receives an output voltage signal from the bridge circuit and provides an input signal to the control means that is indicative of the relative positions of the magnet and the magnetoresistive sensor.

19. The device of claim 18, wherein the input signal includes a variable activity signal, wherein the variable activity signal received by the control means is indicative of both the frequency and magnitude of the relative motion of the magnet and the magnetoresistive sensor.

20. The device of claim 19, wherein the activity/position circuit includes:

a voltage controlled oscillator that receives the output signal from the bridge circuit and oscillates at a frequency that is proportional to the magnitude of the voltage provided by the bridge circuit; and

a counter which receives an output signal of the voltage controlled oscillator and provides a digital signal indicative of the oscillations of the voltage controlled oscillator; and

wherein

the control means periodically samples the counter value so that the counter value comprises the variable activity signal.

21. An implantable cardiac stimulation device adapted to be implanted in the body of a patient, the device comprising:

a casing adapted to be implanted within the body of a patient;

a controller for controlling the delivery of therapeutic electrical stimulation to the heart of the patient;

a magnet positioned within the casing;

a magnetoresistive sensor positioned within the casing, wherein the magnet and the magnetoresistive sensor are mounted so as to be moveable with respect to each other;

wherein

the magnetoresistive sensor produces a position signal that is indicative of the magnetic field sensed by the magnetoresistive sensor such that the position signal is indicative of the relative position of the magnet and the magnetoresistive sensor; and

an activity/position circuit that receives the position signal and provides a corresponding activity signal representative of variances in the position signal to the controller so as to allow the controller to adjust the delivery of therapeutic electrical stimulation to the heart of the patient responsive, at least in part, to the activity signal and the position signal.

22. The device of claim 21, wherein the activity signal received by the controller is indicative of both the frequency and magnitude of the relative motion of the magnet and the magnetoresistive sensor.

23. The device of claim 22, wherein the activity/position circuit comprises:

a voltage controlled oscillator that receives the output signal from the bridge circuit and oscillates at a frequency that is proportional to the magnitude of the voltage provided by the bridge circuit; and

a counter which receives the output signal of the voltage controlled oscillator and provides a digital signal indicative of the oscillations of the voltage controlled oscillator and wherein the controller periodically samples the counter value so that the counter value comprises the activity signal.

24. The device of claim 21, further comprising a substrate positioned within the casing the substrate having a first and a second surface wherein the magnetoresistive sensor is mounted on the substrate and wherein the magnet is movably mounted to the substrate so that when the casing is implanted in the body of a patient, activity of the patient results in the magnet moving with respect to the magnetoresistive sensor so that the magnetoresistive sensor produces the position signal that is indicative of the relative positions of the magnet and the magnetoresistive sensor.

25. The device of claim 24, further comprising:

a mounting block that is positioned on the first surface of the substrate; and

a flexible cantilevered beam that is attached to the mounting block so that the flexible cantilevered beam extends outward from the mounting block wherein the magnet is mounted on the outer end of the flexible cantilevered beam so as to be positioned adjacent to the magnetoresistive sensor.

26. The device of claim 21, wherein the magnetoresistive sensor is comprised of a magnetoresistive sensor formed out of giant magnetoresistive (GMR) materials.

27. The device of claim 21, wherein the magnetoresistive sensor is comprised of a bridge circuit having at least one resistor formed out of giant magnetoresistive (GMR) materials.

28. The device of claim 21, wherein the controller is adapted to increase the pacing rate of pacing pulses that are delivered to the heart when the activity signal indicates that the patient is more active.

29. A method of delivering therapeutic electrical stimulation to the heart of a patient comprising the steps of:

sensing an output signal of a magnetoresistive sensor that is implanted within the body of a patient wherein the output signal is indicative of the relative position of the magnetoresistive sensor and a magnet implanted within the body of the patient; and

adjusting the delivery of therapeutic electrical stimulation to the heart based, at least in part, on the output signal of the magnetoresistive sensor.

30. The method of claim 29, wherein the sensing step is comprised of sensing the output signal of a giant magnetoresistive (GMR) sensor that is implanted within the body of the patient in proximity to the magnet, wherein the magnet is mounted so as to be movable with respect to the giant magnetoresistive sensor.

31. The method of claim 30, wherein the output signal has an AC component and a DC component, further comprising the step of providing a rectified portion of the AC component of output signal to a voltage controlled oscillator that oscillates at a frequency that is proportional to the magnitude of the output signal and then providing an output signal from the voltage controlled oscillator to a counter that provides a counter value signal that is indicative of the oscillations of the voltage controlled oscillator, wherein the counter value signal is indicative of patient activity.

32. The method of claim 29, wherein the step of adjusting the delivery of therapeutic electrical stimulation to the heart comprises increasing the pacing rate of pacing pulses being delivered to the heart in response to receiving an output signal that is indicative of greater physical activity on the part of the patient.

33. The method of claim 29, wherein the step of adjusting the delivery of therapeutic electrical stimulation to the heart comprises decreasing the pacing rate of pacing pulses being delivered to the heart in response to receiving an output signal that is indicative of lesser physical activity on the part of the patient.

34. The method of claim 29, wherein the step of adjusting the delivery of therapeutic electrical stimulation to the heart comprises adjusting the pacing rate in response to changes in position of the patient'"'"'s body.