| 摘要 |
A differential lead impedance comparison apparatus (10) senses lead impedance and compensates for patient-to-patient and electrode variability. A bridge circuit (12) is connected to one end of electrode conductors (22, 24 and 26) in an ECG Leads I configuration. The other end of the conductors (22, 24 and 26) are connected to a patient (18) via electrodes (RA, LA and LL). Leads formed in part by RA, LA and LL and the respective conductors (22, 24 and 26) have lead impedances (Rb, Ra, and Rc). Constant current sources (11, 12 and 13) are connected to the conductors (22, 24 and 26) and supply constant AC currents (I1, I2 and I3). A first bridge output voltage (VM) is produced by I1 and a combination 32 of Ra, Rb, and Rc. A second bridge output voltage (VP) is produced by I2 and a combination 34 of Ra, Rb, and Rc. A differential amplifier circuit (14) differentially amplifies the VM and VP voltages to produce differential voltages (VOM and VOP). Demodulators (DM1 and DM2) demodulate VOM and VOP to produce differential impedance voltages (V1M and V1P). A first comparator (OA3) changes states and produces a high logic output when V1M equals or exceeds a first threshold level (VTH1). A second comparator (OA4) changes states and produces a high logic output when V1P equals or exceeds a second threshold level (VTH2). An exclusive OR gate (G1) produces a high logic output (VOUT) when one and only one of OA3 or OA4 produce a high logic output.
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