No abstract

Aiming at a totally implantable ventricular assist device (VAD), a vibrating flow pump (VFP) was developed in Tohoku University. A transcutaneous energy transmission system (TETS) using an amorphous fiber was developed for the totally implantable VAD system. The VFP works with a higher frequency than the natural heart of a biological system, a frequency of 10-50 Hz. In this research, animal experiments on left heart bypass were performed with healthy goats. Blood from the apex of the left ventricle was received and was sent to the aorta so that an adequate supporting effect of the left heart was provided. In particular, the depression effect of the left ventricle was obvious. As a result, sufficient artificial heart flow was provided. For a totally implantable type VAD, left heart bypass of almost 100% may become necessary in some situations. Therefore, apex approaches of left heart bypass may be desirable. From an anatomical consideration, an apex of the heart is suitable for the VFP of this totally implantable type. In the left heart bypass for which the apex of the heart was used, an almost 100% bypass was possible. This is a requirement that is important when waiting for recovery of sufficient cardiac function. It is also important that left heart circulation is maintained fully by an artificial heart of the complete implantation type. The VFP was considered to be useful as a totally implantable type artificial heart from the results.

For the development of a totally implantable ventricular assist system (VAS), we have been developing the vibrating flow pump (VFP), which can generate oscillated blood flow with a relatively high frequency (10-50 Hz) for a totally implantable system. In this study, effects of left ventricular assistance with this unique oscillated blood flow were analyzed by nonlinear mathematics for evaluation as the entire circulatory regulatory system, not as a separate part of the system. Left heart bypasses using VFPs from the left atriums to the descending aortas were performed in chronic animal experiments using healthy adult goats. Electrocardiogram (ECG), arterial blood pressure, VFP pump flow, and flow of the descending aorta data taken while the goats were awake were recorded in the data recorder and analyzed in the personal computer system through the AD convertor. Using nonlinear mathematics, time series data were embedded into the phase space, and the Lyapunov numerical method, fractal dimension analysis, and power spectrum analysis were performed to evaluate the nonlinear dynamics. During left ventricular assistance with the VFP, Mayer wave fluctuations were decreased in the power spectrum, the fractal dimension of the hemodynamics was significantly decreased, and peripheral vascular resistance was significantly decreased. These results suggest that nonlinear dynamics, which mediate the cardiovascular dynamics, may be affected during LV bypass with oscillated flow. Decreased power of the Mayer wave in the spectrum caused the limit cycle attractor of the hemodynamics and decreased the peripheral resistance. Decreased sympathetic discharges may be the origin of the decreased Mayer wave and fractal dimension. These nonlinear dynamical analyses may be useful to design the optimal VAS control.

To analyze the autonomic nervous system during left heart bypass with a vibrating flow pump (VFP), fluctuations in hemodynamic derivatives were evaluated by the spectral analysis method using fast fourier transform methodology. After the left pleural cavity was opened through the fourth intercostal space under general anesthesia, a VFP was implanted as the left heart bypass device in chronic animal experiments using 3 healthy adult goats. Hemodynamic parameters with and without VFP assistance were recorded on magnetic tape in awake animals and were analyzed by computer through an analog to digital convertor. Power spectral analysis was performed on a beat-to-beat basis for the evaluation of the fluctuations. During left heart bypass with the VFP, Mayer wave fluctuations were decreased significantly although respiratory waves were not changed significantly. These results suggest that sympathetic nervous system modulation was changed under the influences of the left heart bypass with VFP. By using this analysis methodology, truly physiologic ventricular assistance may be achieved.

In the clinical application of supporting circulation, the treatment of a patient with pulmonary hypertension is very important. We developed the electromagnetically driven vibrating flow pump (VFP) as a totally implantable type ventricular assist system. The artificial heart driven by electromagnetic forces creates high speed oscillation flow around 10-50 Hz. Assistance by high-speed oscillation flow has an interesting influence on the cardiovascular system. In this study, we carried out research on the influence such oscillation flow had on the pulmonary arterial vessels, and the supporting flow wave-form that controlled pulmonary vascular resistance was considered. Six healthy adult goats of both sexes were used in the experiments. We carried out inhalation anesthesia and performed intubation. The thorax was opened through left fourth rib resection. Right heart bypass was performed from the right atrium to the pulmonary artery. The flow of right heart assistance was maintained within 20-25% of total flow. Our purpose was to add flow of a specific high frequency to the right heart circulation. The hemodynamic parameters were recorded on a magnetic tape data recorder and input into a computer through an A-D converter. A result identified was that the pulmonary vascular resistance changed according to the alteration of the driving frequency of the VFP even during the same flow assistance. The resistance of the pulmonary arterial vessels became smaller when the driving of the VFP of 30 Hz was added to the right heart circulation. This was significant even when compared with continuous flow right heart assist. The characteristics of impedance appeared to have interesting alterations as well. Control of pulmonary vascular resistance by right heart assistance becomes possible if these results are applied. Accordingly, it may become one of the choices for treatment of a patient with pulmonary hypertension.