Accelerometer count calculation for activity signal for an implantable medical device

• US 6,449,508 B1
• Filed: 10/21/1999
• Issued: 09/10/2002
• Est. Priority Date: 10/21/1999
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Sheldon, Todd J., Ruzin, Donald
• Primary Examiner(s): Schaetzle, Kennedy
• Assistant Examiner(s): DROESCH, KRISTEN L
• Application Number:
  US09/422,835
• Time in Patent Office: 1,055 Days
• Field of Search: 600/587, 600/595, 600/509, 607/9, 607/17-19, 128/902
• US Class Current: 607/19
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration

Abstract

Different levels of accelerometer output are monitored separately and the outputs from these separate monitorings are combined with weighted values to produce a more responsive accelerometer output or count signal. The value of the weights varies with the level monitored. The method and apparatus can be used independently or combined with other cardiac demand signals to produce a pacing rate or target pacing rate signal or can provide data for monitoring, research, or therapeutic intervention.

Claims

1. An activity count producing circuit determining activity count values in an (Implantable Medical Device) IMD, comprising:

means for receiving amplitude and frequency varying output signal from an accelerometer in the IMD,

a plurality of threshold circuits receiving the accelerometer output signal, each threshold circuit of the plurality of threshold circuits having a corresponding plurality of threshold levels and producing sensor count outputs corresponding to amplitude components of the accelerometer output signal that exceed a corresponding threshold level of the plurality of threshold levels for each of the plurality of threshold circuits to produce a count of a number of times each of the corresponding threshold levels are exceeded, and,

combining circuit means for combining the sensor count outputs from said plurality of threshold circuits.

2. An activity count producing circuit as set forth in claim 1 further comprising means for weighting the sensor count outputs, and summing the zero crossings or time periods over the plurality of thresholds to produce an activity count signal.

3. An activity count producing circuit as set forth in claim 1, wherein a first threshold level corresponding to a first threshold circuit of the plurality of threshold circuits is approximately equal to a first signal level in a first setting and a second signal level, not equal to the first setting, in a second setting, and a second threshold level corresponding to a second threshold circuit of the plurality of threshold circuits is approximately equal to a third signal level in the first setting and a fourth signal level, not equal to the third signal level, in the second setting.

4. A rate-responsive implantable medical device having an accelerometer sensor responsive to patient activity to produce a sensor output signal indicative of the level of patient activity, comprising:

a plurality of threshold circuits, each threshold circuit having a different threshold level and producing activity count signals in response to the sensor output signal being greater than the threshold level of the threshold circuit, each threshold circuit having an input to receive the sensor output signal and an output providing the activity count signals;

a first switch sequentially coupling the sensor output signal to the input of each of the threshold circuits;

an activity count processor producing a sensor count signal as a function of the activity count signals produced by the threshold circuits;

a second switch sequentially coupling the output of each threshold circuit to the activity count processor; and

means for controlling the first and second switches to couple each threshold circuit to the accelerometer sensor and to the activity count processor for a predetermined dwell time.

5. An implantable medical device for implantation within a user and having an accelerometer for producing a sensing output signal representing activity levels of the user, comprising:

a plurality of threshold circuits receiving the sensing output signal, each threshold circuit of the plurality of threshold circuits having a corresponding variable threshold level and producing activity counts in response to the sensing output being greater than the corresponding variable threshold level;

a combiner circuit combining the activity counts from said plurality of threshold circuits and producing sensor counts; and

wherein a first threshold level corresponding to a first threshold circuit of the plurality of threshold circuits is approximately equal to a first signal level in a first setting and a second signal level, not equal to the first signal level, in a second setting, and a second threshold level corresponding to a second threshold circuit of the plurality of threshold circuits is approximately equal to a third signal level in the first setting and a fourth signal level, not equal to the third signal level, in the second setting.

6. A method for producing a measure of activity from an accelerometer comprising:

sampling an accelerometer output signal for a short first period of time in a first circuit of a set of accelerometer monitoring and count producing circuits;

producing a count representing a level of activity sensed by said first circuit using a threshold level corresponding to the first circuit;

sampling an accelerometer output signal for a short next through last of a set of periods of time in a next through last set of circuits of said set of accelerometer monitoring and count producing circuits;

producing counts representing a level of activity sensed by said next through last set of circuits using threshold levels corresponding to the next through last set of circuits;

weighting said counts at a predetermined weight unique to each of said set of circuits; and

producing a weighted sensor count output from each count produced by each of said set of circuits, wherein the threshold levels utilized in the steps of producing counts corresponds to respective first signal levels for the first circuit and the next through last set of circuits in a first setting, and respective second signal levels, not equal to the first signal levels, for the first circuit and the next through last set of circuits in a second setting.

7. The method of claim 6 wherein said step of producing a weighted sensor count output from each count produced by each of said set of said circuits is produced seriatim.

8. A method for generating sensor counts representing activity levels of a user of an implantable medical device, comprising the steps of:

generating sensing outputs corresponding to activity levels of the user;

generating, in response to the sensing outputs, a first count using a first threshold level and a second count using a second threshold level; and

combining the first count and the second count and outputting corresponding sensors counts, wherein the first threshold level is approximately equal to a first signal level in a first setting and a second signal level not equal to the first signal level in a second setting, and the second threshold level is approximately equal to a third signal level in the first setting and a fourth signal level, not equal to the third signal level, in the second setting.