Abstract
For the biofeedback control of blood pressure, the instantaneous blood pressure should be presented to the patient. We developed a new Method to indicate blood pressure instantaneously. In recent years it has become possible to measure the waveform of aortic blood pressure non-invasively and continuously. The waveform of aortic pressure includes much useful hemodynamic information. The pressure wave consists of forward and backward propagation waves. The backward propagation wave is reflected mainly from the junction of the arterial tree, and the time between the forward and backward waves is the double propagation time between the heart and the effective reflection point. The time between these waves can be measured by an auto-correlation method, but the measurement error of this method is too large to allow one to estimate the exact effective reflection point, because the forward and backward waves overlap each other. In this paper a new analytic method based on the cepstrum is proposed. Using our method, we can recognize on the cepstrum that the forward and backward waves of various shapes are separated clearly. There is a cross relationship between the propagation delay time and the quefrency of the cepstrum. To evaluate this method, a simulation model of the systemic circulatory system is proposed and used. In this model the arterial tree is divided into 128 segments. Each segment is represented by a four-terminal electrical network. Calculated waveforms obtained from this model are quite similar to the measured waveform from patients. Also the reflection point estimated by this method agrees with that of simulation model.
