Method of detecting signal clipping in a wearable ambulatory medical device

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.

What is claimed is: 
     
         1 . A wearable medical device, comprising:
 at least one sensing electrode configured to sense a cardiac signal of a patient;   an acquisition circuit, operatively coupled to the at least one sensing electrode, configured to process the cardiac signal;   at least one processor configured to detect a cardiac arrhythmia based on the processed cardiac signal; and   a signal conditioning and control unit, operatively coupled to the acquisition circuit and the at least one processor, the signal conditioning circuit configured to
 monitor the cardiac signal during processing by the acquisition circuit, 
 control the processing of the cardiac signal performed by the acquisition circuit, 
 identify one or more corrupted portions of the processed cardiac signal and flag the one or more corrupted portions of the processed cardiac signal with one or more markings indicating the one or more corrupted portions of the processed cardiac signal are compromised to prevent misdetection of the processed cardiac signal by the at least one processor, and 
 provide the processed cardiac signal to the at least one processor, the processed cardiac signal comprising the flagged one or more corrupted portions. 
   
     
     
         2 . The wearable medical device of  claim 1 , wherein the cardiac signal comprises an ECG signal and wherein the signal conditioning and control unit identifies the one or more corrupted portions of the processed signal based upon a comparison with one or more predetermined thresholds, the one or more predetermined thresholds being based on a normal range of a human ECG signal. 
     
     
         3 . The wearable medical device of  claim 2 , wherein the acquisition circuit comprises one or more gain stages to amplify the cardiac signal and wherein the one or more predetermined clipping thresholds are further based upon a gain of the one or more gain stages. 
     
     
         4 . The wearable medical device of  claim 1 , wherein the acquisition circuit comprises at least one programmable attenuation/gain stage and wherein the signal conditioning and control unit comprises an automatic level control unit to vary an amount of attenuation/gain provided by the programmable attenuation/gain stage. 
     
     
         5 . The wearable medical device of  claim 4 , wherein the signal conditioning and control unit is configured to temporarily disable functionality of the automatic level control unit responsive to flagging one or more portions of the cardiac signal as compromised. 
     
     
         6 . The wearable medical device of  claim 1 , wherein the acquisition circuit comprises a filter and wherein the signal conditioning and control unit is configured to detect high frequency noise in the cardiac signal and adjust a cutoff frequency of the filter responsive to detecting the high frequency noise. 
     
     
         7 . The wearable medical device of  claim 1 , further comprising an analog to digital converter, electrically coupled to the acquisition circuit, to digitize the processed cardiac signal and provide a digitized cardiac signal to the signal conditioning and control unit. 
     
     
         8 . The wearable medical device of  claim 1 , wherein the wearable medical device comprises a wearable defibrillator. 
     
     
         9 . The wearable medical device of  claim 4 , wherein the automatic level control unit is configured to determine whether a voltage level of the cardiac signal is above a threshold level and to decrease the amount of gain provided by the at least one programmable attenuation/gain stage responsive to a determination that the voltage level of the cardiac signal is above the threshold level. 
     
     
         10 . The wearable medical device of  claim 4 , wherein the automatic level control unit is configured to determine whether a voltage level of the cardiac signal is below a threshold level and to increase the amount of gain provided by the at least one programmable attenuation/gain stage responsive to a determination that the voltage level of the cardiac signal is below the threshold level. 
     
     
         11 . The wearable medical device of  claim 4 , wherein the signal conditioning circuit is configured to flag the one or more corrupted portions of the processed cardiac signal with the one or more markings in response to a determination that the voltage level of the cardiac signal is approaching the clipping threshold before the at least one programmable attenuation/gain stage. 
     
     
         12 . A wearable medical device, comprising:
 at least one sensing electrode configured to sense a cardiac signal of a patient;   an acquisition circuit, operatively coupled to the at least one sensing electrode, configured to process the cardiac signal; and   a signal conditioning and control unit, operatively coupled to the acquisition circuit, configured to
 monitor the cardiac signal during processing by the acquisition circuit; 
 adjust at least one of a gain and an attenuation applied by the acquisition circuit to the cardiac signal based on one or more predetermined clipping thresholds for the cardiac signal, wherein at least one of the one or more predetermined clipping thresholds is determined based on at least two of a voltage range of an ECG of a human patient, a maximum output voltage level of one or more gain stages of the acquisition circuit, and a current gain setting of the one or more gain stages of the acquisition circuit; and 
 identify one or more corrupted portions of the processed cardiac signal and flag the one or more corrupted portions of the processed cardiac signal with one or more markings indicating that one or more portions of the cardiac signal are compromised in response to a determination that a voltage level of the cardiac signal is approaching the one or more predetermined clipping thresholds. 
   
     
     
         13 . The wearable medical device of  claim 12 , wherein the acquisition circuit comprises at least one programmable attenuation/gain stage and wherein the signal conditioning and control unit comprises an automatic level control unit to vary an amount of attenuation/gain provided by the at least one programmable attenuation/gain stage based on the processed cardiac signal and the one or more predetermined clipping thresholds. 
     
     
         14 . The wearable medical device of  claim 13 , wherein the signal conditioning circuit is configured to flag the one or more corrupted portions of the processed cardiac signal with the one or more markings in response to a determination that a voltage level of the cardiac signal is approaching the one or more predetermined clipping thresholds before the at least one programmable attenuation/gain stage. 
     
     
         15 . The wearable medical device of  claim 12 , further comprising an analog to digital converter, electrically coupled to the acquisition circuit, to digitize the processed cardiac signal and provide a digitized cardiac signal. 
     
     
         16 . The wearable medical device of  claim 12 , wherein the acquisition circuit comprises at least one filter to remove high frequency noise from the cardiac signal. 
     
     
         17 . A wearable medical device, comprising:
 at least one therapy electrode to apply at least one therapeutic shock to a patient;   at least one physiological sensor to provide a physiological sensor signal;   an acquisition circuit, operatively coupled to the at least one physiological sensor, to process the physiological sensor signal; and   a controller, operatively coupled to the acquisition circuit, configured to monitor the physiological sensor signal during processing by the acquisition circuit, identify one or more corrupted portions of the physiological sensor signal and flag the one or more corrupted portions of the physiological sensor signal with one or more markings indicating the one or more corrupted portions are compromised to prevent misdetection of a medical condition of the patient, and administer the at least one therapeutic shock to the patient based on one or more unmarked portions of the physiological sensor signal.   
     
     
         18 . The wearable medical device of  claim 17 , wherein the at least one physiological sensor comprises at least one of: an ECG sensor, a blood pressure sensor, an acoustic sensor, a thoracic impedance sensor, a pulse oxygen sensor, and a temperature sensor. 
     
     
         19 . The wearable medical device of  claim 17 , wherein the acquisition circuit comprises a cascade of amplifiers. 
     
     
         20 . The wearable medical device of  claim 17 , wherein the acquisition circuit is configured to process the physiological sensor signal by at least one of amplifying and attenuating the physiological sensor signal. 
     
     
         21 . The wearable medical device of  claim 17 , wherein the wearable medical device comprises a wearable defibrillator. 
     
     
         22 . A method of processing cardiac signals, comprising:
 sensing a cardiac signal of a patient;   processing the cardiac signal;   providing the processed cardiac signal to at least one processor; and   analyzing, using the at least one processor, the processed cardiac signal to detect a cardiac arrhythmia;   wherein processing the cardiac signal includes identifying whether one or more portions of the processed cardiac signal are corrupted; and   wherein providing the processed cardiac signal to the at least one processor includes providing the one or more portions of the processed cardiac signal to the at least one processor along with one or more markings indicating that the one or more corrupted portions of the processed cardiac signal are compromised to prevent misdetection of the processed cardiac signal by the at least one processor.   
     
     
         23 . The method of  claim 22 , wherein processing the cardiac signal further includes amplifying the cardiac signal, the method further comprising:
 varying an amount of gain applied to the cardiac signal responsive to providing the one or more portions of the processed cardiac signal to the at least one processor along with the one or more markings.   
     
     
         24 . The method of  claim 22 , wherein processing the cardiac signal further includes amplifying the cardiac signal, the method further comprising:
 determining whether a voltage level of the cardiac signal is one of above a threshold level and below the threshold level; and   at least one of decreasing an amount of gain applied to the cardiac signal responsive to a determination that the voltage level of the cardiac signal is above the threshold level and increasing the amount of gain applied to the cardiac signal responsive to a determination that the voltage level of the cardiac signal is below the threshold level.   
     
     
         25 . The method of  claim 22 , wherein processing the cardiac signal further includes amplifying the cardiac signal using a plurality of gain stages, the plurality of gain stages including a fixed gain stage preceded by at least one programmable attenuation/gain stage, the method further comprising determining whether a voltage level of the cardiac signal is approaching a clipping threshold before or after the at least one programmable attenuation/gain stage.