System and method for receiving telemetry data from an implantable medical device

• US 20020087203A1
• Filed: 01/04/2001
• Published: 07/04/2002
• Est. Priority Date: 01/04/2001
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Bange, Joseph E., Schleifer, Fred, Schmitt, Steven
• Granted Patent: US 6,556,871 B2
• Time in Patent Office: Days
• US Class Current: 607/60
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/37211 Means for communicating with stimulators
• CPC Class Codes: A61N 1/37252 Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data
• CPC Class Codes: H04B 1/1036 with automatic suppression of narrow band noise or interference, e.g. by using tuneable notch filters H04B1/123 takes precedence; filter circuits H03H
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A system and method for receiving telemetry data from implantable medical devices such as cardiac pacemakers with improved noise immunity is disclosed. Ambient noise levels and signal strength are monitored and used to adaptively adjust the detection sensitivity of the receiver. Filtering of the received signal is performed to remove both broadband and narrowband noise. Removal of narrowband noise is accomplished with notch filters that are dynamically adjusted in accordance with a detected noise spectrum.

Claims

1. A system for receiving data in the form of transmit pulses from an implantable medical device, comprising:

an antenna for receiving a transmitted signal from an implantable device;

a matched filter with filter coefficients corresponding to a transmit pulse;

a pulse detector for detecting transmit pulses within the received signal by comparing output values of the matched filter with a pulse threshold value; and

,

a threshold adjustment routine for adjusting the pulse threshold value in accordance with measured peak values of noise and the transmitted signal.

2. The system of claim 1 further comprising an analog-to-digital converter for digitizing the received signal into input signal samples.

3. The system of claim 2 wherein noise peak values are measured at a time when the implantable device is known not to be transmitting in accordance with a telemetry protocol.

4. The system of claim 2 wherein the pulse threshold value is computed as a fraction of a weighted moving average of measured signal peak values that exceed a specified minimum pulse threshold value.

5. The system of claim 4 wherein the minimum pulse threshold value is adjusted in accordance with measured noise peak values.

6. The system of claim 5 wherein the minimum pulse threshold is adjusted by comparing a current minimum pulse threshold value with a measured noise peak value, setting the minimum pulse threshold value equal to the measured noise peak value if the measured noise peak value is greater than the current minimum pulse threshold value, and setting the minimum pulse threshold value equal to a weighted moving average of measured noise peak values if the measured noise peak value is less than the current minimum pulse threshold value.

7. The system of claim 6 wherein the pulse threshold value is left unchanged if the current measured signal peak value is below the current minimum pulse threshold value and set equal to an updated weighted moving average of measured signal peak values otherwise.

8. The system of claim 7 further comprising one or more notch filters for removing narrowband noise from the input signal samples prior to being input to the matched filter, the filters having notch frequencies corresponding to frequency components of the narrowband noise

9. The system of claim 8 further comprising a filter generator for updating filter coefficients of the notch filters so that the notch frequencies correspond to a detected noise spectrum in the input signal samples.

10. The system of claim 9 wherein the filter generator detects a noise spectrum by discrete Fourier transforming a set of input samples to produce a power spectrum of the input signal and subtracting a template spectrum therefrom, the template spectrum corresponding to a representative input signal without noise.

11. The system of claim 10 wherein the filter generator sets the notch frequencies of the notch filters to match those spectral components of the noise spectrum that exceed a specified spectral threshold value.

12. The system of claim 10 wherein the filter coefficients of the notch filters are periodically updated by the filter generator.

13. The system of claim 12 wherein the filter coefficients of the notch filters are updated based upon input samples continuously input into a buffer.

14. The system of claim 9 wherein the notch filters are digital infinite impulse response filters synthesized with notch frequencies corresponding to the detected noise spectrum.

15. The system of claim 2 wherein the data is encoded into the transmitted signal by amplitude shift keying such that the presence or absence of a pulse in the transmitted signal constitutes a binary symbol.

16. An external programmer for a cardiac rhythm management device having incorporated therein the system of claim 9 for receiving data from a cardiac rhythm management device.

18. The method of claim 17 further comprising measuring noise peak values at a time when the implantable device is known not to be transmitting in accordance with a communications protocol.

19. The method of claim 17 further comprising computing the pulse threshold value as a fraction of a weighted moving average of measured signal peak values that exceed a specified minimum pulse threshold value.

20. The method of claim 19 further comprising adjusting the minimum pulse threshold value in accordance with measured noise peak values.

21. The method of claim 20 further comprising adjusting the minimum pulse threshold by comparing a current minimum pulse threshold value with a measured noise peak value, setting the minimum pulse threshold value equal to the measured noise peak value if the measured noise peak value is greater than the current minimum pulse threshold value, and setting the minimum pulse threshold value equal to a weighted moving average of measured noise peak values if the measured noise peak value is less than the current minimum pulse threshold value.

22. The method of claim 21 further comprising leaving the pulse threshold value unchanged if the current measured signal peak value is below the current minimum threshold value and setting the pulse threshold value equal to an updated weighted moving average of measured signal peak values otherwise.

23. The method of claim 21 further comprising:

filtering the input signal samples prior to being input to the matched filter with a plurality of notch filters for removing narrowband noise therefrom, the filters having notch frequencies corresponding to frequency components of the narrowband noise;

detecting a noise spectrum of the input signal samples; and

,

updating filter coefficients of the notch filters so that the notch frequencies correspond to the detected noise spectrum.

24. The method of claim 23 further comprising detecting a noise spectrum by discrete Fourier transforming a set of input samples to produce a power spectrum of the input signal and subtracting a template spectrum therefrom, the template spectrum corresponding to a representative input signal without noise.

25. The method of claim 24 further comprising setting the notch frequencies of the notch filters to match those spectral components of the noise spectrum that exceed a specified spectral threshold value.

17. A method for receiving telemetry data from an implantable medical device, comprising:

receiving a transmitted signal modulated with data from an implantable device;

digitizing the received signal into input signal samples;

filtering the input samples with a matched filter having filter coefficients corresponding to a transmit pulse;

detecting transmit pulses within the input signal samples by comparing output values of the matched filter with a pulse threshold value; and

,

adjusting the pulse threshold value in accordance with measured peak values of noise and the transmitted signal.