Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2000-12-06
2003-01-21
Wolfe, Willis R. (Department: 3747)
Surgery
Diagnostic testing
Cardiovascular
C600S515000, C128S903000
Reexamination Certificate
active
06510339
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an automatic gain control (AGC) apparatus and method for controlling the output from medical devices, and more particularly to an automatic gain control apparatus and method for control of the output from a multi-lead electrocardiogram device.
2. Description of the Related Art
Humans generate a variety of electrical impulses through nerve and muscular activity. Doctors frequently monitor selected impulses to diagnose diseases and otherwise evaluate a patient's health. Impulses from the heart and brain are most frequently monitored. In the case of the heart, electrocardiograms (ECGs) provide doctors with an indication of the heart's electrical activity in both the atria and the ventricles. Since the ECG is reflective of both atrial and ventricular activity, the ECG is particularly useful in evaluating a patient's cardiac rhythm and health.
ECG recordings are derived from electrodes placed on a patient's skin at predetermined locations about the patient's body. The signals picked up by the contacts create particular waveforms dependent upon the number of electrodes and their location on the body. A typical waveform associated with the ECG is the PQRST-complex. The excursions of the PQRST-complex represent the voltage difference at the body's surface sensed by the attached electrodes, typically twelve electrodes, relative to a reference electrode.
The PQRST-complex is indicative of both atrial and ventricular depolarization and repolarization events. The P-wave corresponds to the depolarization of the atria. Atrial depolarization is usually lasts about 0.1 second and has an amplitude of between 0.1 and 0.2 millivolt as sensed by an ECG. The interval of time from the beginning of the P-wave to the beginning of the QRS-complex is called the PR-interval. The PR-interval is normally no longer than 0.2 seconds. The QRS-complex corresponds to ventricular depolarization. Ventricular depolarization usually lasts about 0.08 to 0.10 second and has an amplitude of about 0.5 to 3.0 millivolt as sensed by the ECG. Thus, the QRS-complex typically has a larger amplitude than the P-wave. The increased amplitude is primarily due to the ventricle's greater muscle mass and the depolarization synchronization due to the ventricles' network of nerves. The ST-segment follows the completion of the QRS complex. The ST-segment is a segment of zero voltage. The segment corresponds to the action potential's refractory period when the ventricles remain depolarized. The ST-segment typically lasts about 0.15 second. The T-wave follows the ST-segment. The T-wave corresponds to ventricular repolarization. Repolarization is typically a slower process than depolarization and does not propagate from cell to cell as does depolarization. Thus, the T-wave is typically small in amplitude and lasts between about 0.15 and 0.20 second.
The waveform generated by the voltage changes over time are output as a continuous wave on a monitor or printed on a rhythm strip by the ECG. Doctors can evaluate anomalies in an ECG's output to diagnose diseases and evaluate a patient's overall health. To better enable comparison, the output from an ECG is governed by convention. Particularly, the ECG is configured to maintain the waveform's maximum amplitude between approximately 10 to 20 millimeters as printed or displayed. The printed rhythm strip typically includes a series of horizontal and vertical lines forming a grid. Typically, the lines are one millimeter apart. The horizontal lines represent voltage and, by convention, each line is indicative of a 0.1 millivolt change. The vertical lines represent time and, again by convention, each line is indicative of a 0.04 second interval. To standardize the output, the highest waves typically found in the QRS-complex are set at around 10 mm in height. This height, again set by convention, enables the direct comparison of different outputs. While monitoring a patient, the amplitude of the ECG's output can vary due to a number of physical and physiological changes not related to the condition of the heart. These changes can cause variations in the output not indicative of cardiac function, making interpretation by a physician more difficult. To compensate for these changes, ECG devices are typically equipped with a vertical gain control. The gain control typically requires the operator to switch between a plurality of pre-selected gains to bring the output of the ECG to the desired amplitude. The physician must review the output, determine the appropriate gain setting, and adjust the gain. The attention to the ECG's gain setting diverts the physician's attention away from the patient. Thus, a need exists for a method and apparatus that automatically adjust the gain settings on the ECG.
The present invention meets the above needs and provides additional advantages and improvements that will be evident to those skilled in the art upon review of the following description and figures.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for automatic gain adjustment for an ECG's output. The present invention allows the monitoring of an ECG's output without affecting the ECG's normal processing. Further, the present invention provides an AGC that may be defeatable, allowing a user to switch between manual and automatic gain control.
The method includes receiving data from an ECG and using the data to determine an appropriate gain setting. Thus, the method first involves receiving data representative of at least one vector from an electrocardiogram device. The data indicative of the vector used by the automatic gain control may be decimated or only a fraction of the data used in determining the appropriate gain setting. The amplitude of the vector is then determined. The amplitude may be determined by comparing the amplitude of a particular vector to a baseline. The baseline being established by taking an average amplitude of the input vector over a period of time. Data above a particular exclusion threshold may be excluded from the baseline value to prevent the inclusion of aberrant data in the calculation. The amplitude may be determined for a particular vector during a measurement window. The measurement window may be initiated by the amplitude reaching or exceeding an initiation threshold. The amplitude of the vector is then compared to a plurality of thresholds. The particular thresholds reached or exceeded establish gain values used to determine the appropriate gain setting. The gain setting is then adjusted based on the gain values determined in the prior steps. The gain value may be input into an algorithm and the relationship between the gain values used to determine the gain setting.
The method of the present invention may be implemented in a device for auto-gain control. The specific components may be implemented through circuits, software or a combination of the two. The device includes at least one circle buffer for storing data indicative of output of an electrocardiograph device. A baseline is connected to the circle buffer to read the stored data. The detection circuit establishes a baseline or running average for the amplitude from the data. A maximum amplitude detection circuit determines the maximum amplitude from a particular set of data relative to the baseline. A comparator circuit compares a plurality of amplitudes from the maximum amplitude detection circuit with a plurality of thresholds to establish a set of gain values. The set of gain values are provided to a decision circuit for altering a gain setting for the output of the electrocardiograph device based on a relationship between set of gain values.
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Kovtun Vladimir V.
Paulson Paul D.
Cardiac Pacemakers Inc.
Nikolai Thomas J.
Nikolai & Mersereau , P.A.
Wolfe Willis R.
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