| 摘要 |
An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart as an indicator of cardiac stroke volume, wherein common interfering signals such as the intracardiac electrogram, myoelectric signals, pacing artifacts and pacing after-potentials are eliminated from the measurement of impedance. The cardiac pacemaker senses varying impedance of the heart by discharging an active capacitor through an electrode implanted within the heart to a second electrode or to the case or can of the pacemaker. The active capacitor is discharged for a selected short period of time after which the voltage remaining on the capacitor is measured. To minimize error in the measurement of voltage discharged from the active capacitor, the selected short period of time for discharge can be varied dynamically by the cardiac pacemaker. Prior to discharge of this active capacitor, however, the cardiac pacemaker samples the electrical condition of the heart or the body of the patient between the two electrodes by charging a passive capacitor. The sampled voltage on the passive capacitor is subtracted from the residual voltage on the active capacitor and the resulting voltage is used to adjust the rate of the pacemaker.
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