Continuous monitoring of autonomic nerve information for the control of an artificial heart

To drive an artificial heart system optimally, information from the autonomic nervous system may be needed; however, it is very difficult to monitor autonomic nerve discharges continuously. In this study, we propose a new automatic control algorithm for a total artificial heart (TAH) using fluctuations in the circulatory system. It was reported that fluctuations in hemodynamics reflect ongoing information from the autonomic nervous system. A Mayer wave at 0.1 Hz was reported to reflect sympathetic information. We observed fluctuations in vascular resistance, which can be measured during use of an artificial heart. Four adult goats were used for the experiments. Through a left thoracotomy, hemodynamic parameters were measured during chronic animal experiments. All time series data were recorded on magnetic tape. Quantitative analysis, statistics, and spectral analysis were carried out on a computer through an analog-digital (AD) converter. A Mayer wave peak was clearly recognized in all goats in the spectrum of vascular resistance. A band pass filter was used to convert this information to automatic control. Time series curves of the Mayer wave of vascular resistance were provided, and compared with the time series curve of the cardiac output. After a change in the Mayer wave, increase in cardiac output was observed. This phenomenon may be interpreted as sympathetic nervous control of changes in cardiac output. These results suggest that an artificial heart may be controlled by the measurement of the Mayer wave of vascular resistance, making it possible to control an artificial heart with neural information.

Development and evaluation of totally implantable ventricular assist system using a vibrating flow pump and transcutaneous energy transmission system with amorphous fibers

We have developed a vibrating flow pump (VFP) that can generate oscillated blood flow with a relatively high frequency (10-50 Hz) for a totally implantable ventricular assist system (VAS). To evaluate the newly developed VAS, left heart bypasses, using the VFP, were performed in chronic animal experiments. Hemodynamic parameters were recorded in a data recorder in healthy adult goats during an awake condition and analyzed in a personal computer system through an alternating-direct current converter. Basic performance of the total system with a transcutaneous energy transmission system were satisfactory. During left ventricular assistance with the VFP, Mayer wave fluctuations of hemodynamics were decreased in the power spectrum, the fractal dimensions of the hemodynamics were significantly decreased, and peripheral vascular resistance was significantly decreased. These results suggest that cardiovascular regulatory nonlinear dynamics, which mediate the hemodynamics, may be affected by left ventricular bypass with oscillated flow. The decreased power of the Mayer wave in the spectrum caused the limit cycle attractor of the hemodynamics and decreased peripheral resistance. These results suggest that this newly developed VAS is useful for the totally implantable system with unique characteristics that can control hemodynamic properties.