| 摘要 |
Thoracic impedance (22, 23) and EKG signals (25a, 25b) are processed for improved resolution and accuracy. EKG signals are adaptively processed (26, 28) by digitizing, filtering, differentiating and raising the resultant differential by a power greater than one to emphasize changes in the slope. Blocks of the processed EKG data are analyzed (30) to identify peak amplitude and to compare spacing between peak amplitudes to more accurately identify R wave peaks. Stroke volume is determined from a thoracic impedance signal and its time derivative. Preferably, a time- frequency distribution is taken of the time derivative thoracic impedance signal after low- and high-pass filtering to identify B and X wave events which are used to determine ventricular ejection time and dZ/dt min for heart stroke volume determination by conventional methods. Alternatively, stroke volume is determined by a new relationship between a product of a pair of impedances simultaneously sensed on opposing sides of a heart at the heartbeat's peak.
|
