METHOD OF DETECTING SIGNAL CLIPPING IN A WEARABLE AMBULATORY MEDICAL DEVICE

• US 20120289809A1
• Filed: 03/23/2012
• Published: 11/15/2012
• Est. Priority Date: 03/25/2011
• Status: Active Grant

• Current Assignee: Zoll Medical Corporation (Asahi Kasei Corporation)
• Original Assignee: Zoll Medical Corporation (Asahi Kasei Corporation)
• Inventors: Kaib, Thomas E., Volpe, Shane S., Macho, John D.
• Granted Patent: US 8,600,486 B2
• Time in Patent Office: Days
• US Class Current: 600/388
• CPC Class Codes: A61B 2562/0204 Acoustic sensors
• CPC Class Codes: A61B 5/02055 Simultaneously evaluating both cardiovascular condition and temperature
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/25 Bioelectric electrodes therefor
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/303 Patient cord assembly, e.g. cable harness
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• CPC Class Codes: A61B 5/6801 specially adapted to be attached to or worn on the body surface
• CPC Class Codes: A61B 5/6805 Vests
• CPC Class Codes: A61B 5/6831 Straps, bands or harnesses
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R
• CPC Class Codes: A61N 1/3987 characterised by the timing or triggering of the shock
• CPC Class Codes: H03G 7/002 in untuned or low-frequency amplifiers, e.g. audio amplifiers H03G7/007, H03G7/001, H03G7/008, H03G7/02, H03G7/06 take precedence
• CPC Class Codes: H03G 7/005 using discontinuously variable devices, e.g. switch-operated

Abstract

A wearable medical device and method of detecting clipping of ECG signals is disclosed. In one embodiment, the wearable medical device comprises a plurality of ECG sensing electrodes configured to sense an ECG of a patient and an ECG acquisition circuit electrically coupled to a pair of the plurality of ECG sensing electrodes and configured to provide an amplified and conditioned analog ECG signal, a programmable attenuation/gain stage electrically coupled between a first gain stage and a second gain stage, an ADC electrically coupled to the ECG acquisition circuit to receive and digitize the amplified and conditioned analog ECG signal and provide a digitized ECG signal, and a signal conditioning and control unit electrically coupled to the ECG acquisition circuit and the ADC to receive and monitor the digitized ECG signal and to detect clipping of the amplified and conditioned analog ECG signal based upon the digitized ECG signal.

Claims

1. A wearable medical device, comprising:

a plurality of ECG sensing electrodes configured to sense an ECG of a patient;

an ECG acquisition circuit electrically coupled to a pair of the plurality of ECG sensing electrodes and configured to provide an amplified and conditioned analog ECG signal, the ECG acquisition circuit including a programmable attenuation/gain stage electrically coupled between a first gain stage and a second gain stage;

an analog to digital converter electrically coupled to the ECG acquisition circuit to receive and digitize the amplified and conditioned analog ECG signal and provide a digitized ECG signal; and

a signal conditioning and control unit electrically coupled to the ECG acquisition circuit and the analog to digital converter to receive and monitor the digitized ECG signal and to detect clipping of the amplified and conditioned analog ECG signal based upon the digitized ECG signal.

2. The wearable medical device of claim 1, wherein the signal conditioning and control unit includes an automatic level control unit electrically coupled to the programmable attenuation/gain stage, and configured to vary an amount of attenuation/gain provided by the programmable attenuation/gain stage based on the digitized ECG signal.

3. The wearable medical device of claim 2, wherein the automatic level control unit is configured to determine whether a voltage level of the digitized ECG signal is above a threshold level and configured to increase the amount of attenuation provided by the programmable attenuation/gain stage.

4. The wearable medical device of claim 2, wherein the automatic level control unit is configured to determine whether a voltage level of the digitized ECG signal is below a threshold level and configured to decrease the amount of attenuation provided by the programmable attenuation/gain stage.

5. The wearable medical device of claim 2, wherein the signal conditioning and control unit includes an analog clipping detection and control unit electrically coupled to the programmable attenuation/gain stage, and configured to determine whether a voltage level is approaching a clipping threshold.

6. The wearable medical device of claim 5, wherein the analog clipping detection and control unit is configured to determine the voltage level before programmable attenuation/gain stage.

7. The wearable medical device of claim 6, wherein the amplified and conditioned analog ECG signal is marked as compromised in response to a determination that the voltage level is approaching the clipping threshold before the programmable attenuation/gain stage.

8. The wearable medical device of claim 5, wherein the analog clipping detection and control unit is configured to determine the voltage level after the programmable attenuation/gain stage.

9. The wearable medical device of claim 8, wherein the analog clipping detection and control unit attenuates the amplified and conditioned analog ECG signal in response to a determination that the voltage level is approaching the clipping threshold after the programmable attenuation/gain stage.

10. The wearable medical device of claim 5, wherein the clipping threshold is determined based on a voltage range of an ECG of a human patient, a maximum output voltage level and a current gain setting of at least one of the first gain, the programmable attenuation/gain stage and the second gain stage.

11. The wearable medical device of claim 1, further including a low noise instrumentation amplifier electrically coupled to the pair of the plurality of ECG sensing electrodes and the first gain stage.

12. The wearable medical device of claim 1, further including a low pass filter electrically coupled to at least one of the second gain stage and the analog to digital converter.

13. A method of detecting clipping of ECG signals in a wearable medical device, the method comprising acts of:

sensing an ECG signal of a patient using ECG sensing electrodes;

amplifying the sensed ECG signal using a first gain stage;

conditioning the amplified ECG signal from the first gain stage using a programmable attenuation/gain stage;

amplifying the conditioned ECG signal from the programmable attenuation/gain stage using a second gain stage;

receiving and digitizing the amplified and conditioned analog ECG signal to provide a digitized ECG signal; and

monitoring the digitized ECG signal to detect clipping of the amplified and conditioned analog ECG signal based upon the digitized ECG signal.

14. The method of claim 13, further including varying an amount of attenuation applied by the programmable attenuation/gain stage based on the digitized ECG signal.

15. The method of claim 14, wherein the act of varying the amount includes:

determining whether a voltage level of the digitized ECG signal is above a threshold level; and

increasing the amount of attenuation applied by the programmable attenuation/gain stage.

16. The method of claim 14, wherein the act of varying the amount includes:

determining whether a voltage level of the digitized ECG signal is below a threshold level; and

decreasing the amount of attenuation applied by the programmable attenuation/gain stage.

17. The method of claim 13, further including detecting whether a voltage level is approaching a clipping threshold.

18. The method of claim 17, further including determining the clipping threshold based on a voltage range of an ECG of a human patient, a current gain setting and a maximum output voltage level of at least one of the first gain stage, the programmable attenuation/gain stage and the second gain stage.

19. The method of claim 17, wherein the act of detecting includes marking the amplified and conditioned analog ECG signal as compromised in response to a determination that the voltage level is approaching the clipping threshold before programmable attenuation/gain stage.

20. The method of claim 13, wherein the act of detecting includes attenuating the amplified and conditioned analog ECG signal in response to a determination that the voltage level is approaching the clipping threshold after the programmable attenuation/gain stage.