SYSTEM AND METHOD FOR SMOOTHING SAMPLED DIGITAL SIGNALS

• US 20080243207A1
• Filed: 03/26/2007
• Published: 10/02/2008
• Est. Priority Date: 03/26/2007
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Corndorf, Eric D.
• Granted Patent: US 8,315,709 B2
• Time in Patent Office: Days
• US Class Current: 607/60
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/025 Digital circuitry features of electrotherapy devices, e.g. memory, clocks, processors
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371
• CPC Class Codes: H03M 7/40 Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code

Abstract

Waveforms are digitally sampled and compressed for storage in memory. The compression of the data includes generating a truncated entropy encoding map and using the values within the map to obtain good compression. An encoder further sub-selects values to be encoded and values to remain unencoded to provide an overall compression of the data.

Claims

1. An implantable medical device (IMD) comprising:

a memory;

an analog to digital converter (ADC) configured to receive an analog waveform and sample the waveform into digitized data;

a smoothing filter configured to process the sampled signal and classify each data point into a first type or a second type and to apply a smoothing function to the first type of classified data and to retain a sampled valued for the second type of classified data;

a predictive encoding module operatively coupled with the ADC to generate an encoded waveform data point for each of an equivalent data point from a subset of the digitized data; and

an entropy encoding module operatively coupled with the predictive encoder and configured to selectively replace an encoded waveform data point with a codeword for that data point.

2. The IMD of claim 1, wherein the smoothing filter is configured to determine variability between sampled data points adjacent to a given data point being classified and classifying the given data point into the first type if the variability is less than a predetermined variability value and into the second group if the variability is equal to or greater than the predetermined variability value.

3. An apparatus comprising:

a signal source to provide a digitally sampled signal; and

a smoothing filter configured to process the sampled signal and classify each data point into a first type or a second type and to apply a smoothing function to the first type of classified data and to retain a sampled valued for the second type of classified data.

4. The apparatus of claim 3, further comprising a predictive encoding module configured to encode the classified data.

5. The apparatus of claim 4, further comprising a truncated entropy encoding module configured to selectively replace predicatively encoded data with a codeword.

6. The apparatus of claim 3, wherein the smoothing filter is configured to determine variability between sampled data points adjacent to a given data point being classified and classifying the given data point into the first type if the variability is less than a predetermined variability value and into the second group if the variability is equal to or greater than the predetermined variability value.

7. The apparatus of claim 6, wherein the smoothing function applied to the first type of data is to determine an average value for the given data point and the data points adjacent to the given value.

8. The apparatus of claim 6, wherein the smoothing function applied to the first type of data is to determine a weighted average value for the given data point and the data points adjacent to the given value.

9. A method comprising:

obtaining sampled data;

defining an adjustment set of data points for each given data point;

determining a value for variability in the adjustment set; and

smoothing the given data point relative to the adjustment set if the determined variability is below a predetermined maximum.

10. The method of claim 9 wherein the adjustment set includes the given data point, a first data point immediately preceding the given data point and a second data point immediately subsequent to the given data point.

11. The method of claim 10 wherein determining variability includes measuring a difference in a value between each data point within the adjustment set.

12. The method of claim 10 wherein determining variability includes adding a first absolute value of a difference between the first data point and the given data point and a second absolute value of a difference between the second data point and the given data point.

13. The method of claim 9, wherein smoothing the given data point includes averaging the adjustment set and setting a value of the given data point for subsequent encoding equal to the average value.

14. The method of claim 9, wherein smoothing the given data point includes obtaining a weighted average of the adjustment set and setting a value of the given data point for subsequent encoding equal to the average value.

15. The method of claim 13, further comprising predicatively encoding the sampled data subsequent to selectively smoothing the data.

16. The method of claim 15, further comprising selectively providing entropy encoded codewords for the predicatively encoded data based upon a truncated entropy codeword set.

17. The method of claim 16, wherein entropy encoding is only provided for smoothed data points.

18. The method of claim 16, further comprising:

analyzing the sampled data wherein the sampled data represents cardiac waveforms;

identifying cardiac events; and

entropy encoding portions of the data absent identified cardiac events.

19. The method of claim 18, wherein the determination of variability is utilized in the identification of cardiac events.