Microcontrolled electrocardiographic monitoring circuit with feedback control

• US 8,285,370 B2
• Filed: 10/08/2010
• Issued: 10/09/2012
• Est. Priority Date: 10/08/2010
• Status: Active Grant

• Current Assignee: Zoll Medical Corporation (Asahi Kasei Corporation)
• Original Assignee: Cardiac Science Operating Company (Cardica Incorporated)
• Inventors: Felix, Jason, Bardy, Gust H.
• Primary Examiner(s): Layno, Carl H
• Assistant Examiner(s): Wu, Eugene
• Application Number:
  US12/901,449
• Publication Number:
  US 20120089036A1
• Time in Patent Office: 732 Days
• Field of Search: 600/508, 600/509, 600/519
• US Class Current: 600/509
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/332 Portable devices specially adapted therefor
• CPC Class Codes: A61B 5/333 Recording apparatus specially adapted therefor
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period

Abstract

A microcontrolled electrocardiographic monitoring circuit with feedback control is provided. An input signal path includes an electrode, a low pass filter, and an amplifier connected in-line. The electrode senses an input signal and the amplifier outputs a filtered amplified output signal. A microcontroller circuit includes an input codec, analog-to-digital converter, and feedback generation module. The analog-to-digital converter converts the filtered amplified output signal into a data stream of discrete digital values. The feedback module identifies a pairing of drive resistor settings matched to each discrete digital value, which are output as a digital feedback signal. The output signal path includes an electrode and a buffer connected in-line. A pair of drive resistors is connected in parallel to an input terminal of the buffer and to the output terminals of the feedback module. Each drive resistor is adjusted according to the digital feedback signal, and the electrode provides an output signal.

Claims

1. A microcontrolled electrocardiographic monitoring circuit with feedback control, comprising:

an input signal path comprising an electrode, a low pass filter, and an amplifier, each connected in-line, the electrode configured to sense an input signal via a conductive surface and the amplifier configured to output a filtered amplified output signal;

a microcontroller circuit comprising an input codec, comprising;

an analog-to-digital converter connected to the input signal path through an output of the amplifier and configured to convert the filtered amplified output signal into a data stream of discrete digital values; and

a feedback generator configured to identify a pairing of drive resistor settings matched to each discrete digital value and output the drive resistor settings from the microcontroller circuit as a digital feedback signal through a pair of output terminals; and

an output signal path comprising an electrode and a buffer, each connected in-line, and a pair of drive resistors connected in parallel to an input terminal of the buffer and to the output terminals of the feedback generator, the microcontroller circuit configured to adjust each drive resistor according to the digital feedback signal, and the electrode configured to provide an output signal via a conductive surface.

2. A circuit according to claim 1, further comprising:

a comparator comprised in the feedback generator configured to compare the discrete digital value to a bias saturation threshold for the input signal path and configured to select the digital feedback signal in relation to relative closeness of the discrete digital value to the bias saturation threshold.

3. A circuit according to claim 1, further comprising:

a set of enumerated values stored in a persistent memory that each correspond to a range of bias for the input signal path; and

the microcontroller circuit further comprising a selector configured to select the digital feedback signal from the enumerated values by comparison of the discrete digital value to each range of bias.

4. A circuit according to claim 3, wherein each range of bias corresponds to at least one of percentages of a bias saturation threshold and subthreshold values that are each less than the bias saturation threshold.

5. A circuit according to claim 1, further comprising:

persistent memory connected to the microcontroller circuit via a peripheral serial interface bus, wherein each of the discrete digital values in the data stream are stored into the persistent memory.

6. A circuit according to claim 5, wherein each discrete digital value comprises a voltage representative of an analog cardiac action potential signal, further comprising:

a power supply, the microcontroller circuit configured to be powered by the power supply; and

the microcontroller circuit further comprising a reference compensator configured to determine the voltage of the power supply and normalize the voltage for each of the discrete digital values against depletion of the voltage of the power supply over a monitoring period.

7. A circuit according to claim 6, further comprising:

a reference scaler configured to scale the voltage of the power supply based on a number of write operations into the persistent memory and set the voltage for each of the discrete digital values based upon placement of the specific retrieved discrete digital value within an ordering of all of the retrieved discrete digital values.

8. A circuit according to claim 1, the feedback generator further comprising:

a feedback marker configured to generate and store a feedback marker value into a persistent memory in sequence with the discrete digital values in the data stream.

9. A circuit according to claim 8, the microcontroller circuit further comprising:

a decoder configured to reproduce analog cardiac action potential signals from the discrete digital values; and

an adjuster configured to determine a contribution from feedback from the feedback marker value and subtract the feedback contribution from the analog cardiac action potential signals.

10. A circuit according to claim 9, the microcontroller circuit further comprising:

a reference compensator configured to extend resolution of each discrete digital value as a function of the subtraction of feedback contribution before analog cardiac action potential signals reproduction.

11. A microcontrolled electrocardiographic monitoring circuit with bias saturation feedback, comprising:

an input signal path comprising an electrode, a low pass filter, and an amplifier, each connected in-line, the electrode configured to sense an input signal via a conductive surface and the amplifier configured to output a filtered amplified output signal;

a microcontroller circuit comprising an input codec, comprising;

an analog-to-digital converter connected to the input signal path through an output of the amplifier and configured to convert the filtered amplified output signal into a data stream of discrete digital values;

a feedback generation generator configured to compare the discrete digital value to a bias saturation threshold for the input signal path and configured to select a pairing of drive resistor settings as a digital feedback signal in relation to relative closeness of the discrete digital value to the bias saturation threshold; and

an input/output module configured to output the digital feedback signal through a pair of output terminals;

persistent memory connected to the microcontroller circuit via a peripheral serial interface bus, which stores each of the discrete digital values in the data stream into the persistent memory; and

an output signal path comprising an electrode and a buffer, each connected in-line, and a pair of drive resistors connected in parallel to an input terminal of the buffer and to the output terminals of the feedback;

generator, the microcontroller circuit configured to adjust each drive resistor according to the digital feedback signal, and the electrode configured to provide an output signal via a conductive surface.

12. A circuit according to claim 11, further comprising:

a set of enumerated values stored in the persistent memory that each correspond to lower and upper bounds of bias for the input signal path, path; and

the microcontroller circuit further comprising a selector configured to select configured to select the digital feedback signal from the enumerated values by comparison of the discrete digital value to the lower and upper bounds of bias.

13. A circuit according to claim 12, wherein each range of bias corresponds to at least one of percentages of a bias saturation threshold and subthreshold values that are each less than the bias saturation threshold.

14. A circuit according to claim 11, wherein each discrete digital value comprises a voltage representative of an analog cardiac action potential signal, further comprising:

a power supply, the microcontroller circuit configured to be powered by the power supply; and

a reference compensator configured to determine a voltage for the power supply and configured to normalize each of the discrete digital values against depletion of the voltage of the power supply over a monitoring period.

15. A circuit according to claim 14, further comprising:

a reference scaler configured to scale the voltage of the power supply based on a number of write operations into the persistent memory and set the voltage for each of the discrete digital values based upon placement of the specific retrieved discrete digital value within an ordering of all of the retrieved discrete digital values.

16. A circuit according to claim 11, wherein the electrode comprised in the input signal path and the electrode comprised in the output signal path are spaced less than 6 cm apart.