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United States Patent  [li] Patent Number: 5,615,687
Pritchard  Date of Patent: Apr. 1, 1997
 HEART MONITORING SYSTEM AND METHOD WITH REDUCED SIGNAL ACQUISITION RANGE
 Inventor: Bruce A. Pritchard, McMinnville, Oreg.
 Assignee: Hewlett-Packard Company, Palo Alto, Calif.
 Appl. No.: 567,975
 Filed: Dec. 6, 1995
 Int. CI.6 A61B 5/0402
 U.S. CI 128/696
 Field of Search 128/901, 902,
An ECG system for a 12-lead ECG test includes ten electrodes—consisting of six ventricle electrodes V1-V6, a right arm electrode RA, a left arm electrode LA, a left leg electrode LL, and a right leg electrode RL—which generate electrical signals indicative of heart activity within a human patient. The EGG system also includes a plurality of conductors connected to corresponding electrodes and a signal acquisition system connected to the conductors. The EGG system also has an offset adjustment system operatively coupled to the signal acquisition system. The offset adjustment system identifies a selected voltage level (such as a maximum or minimum voltage level) of at least one of the electrical signals generated by an associated electrode and manipulates that voltage level to produce an offset adjustment signal. This offset adjustment signal is used to bring voltage levels of all of the electrical signals produced by the electrodes within a signal acquisition range of the signal acquisition system. The ECG system further includes a potential adjusting feedback circuit coupled between the offset adjustment system and one of the electrodes (such as the right leg electrode RL) to supply a reference potential to that electrode. The potential tends toward the offset adjustment signal to offset the electric potentials of the human patient by an equal amount. This offset has the effect of moving the range of electrode voltages into the range of the signal acquisition system and yields a maximum signal acquisition range of approximately 300 mV, which can be resolved to 5 uV increments using a 16-bit A/D converter.
17 Claims, 3 Drawing Sheets