Taro Sonobe

Deterministic chaos in the hemodynamics of an artificial heart

To analyze the hemodynamic parameters during prosthetic circulation as an entity, non linear mathematical techniques were used. To compare natural and prosthetic circulation, two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses in chronic animal experiments using adult goats to consitute the biventricular bypass complete prosthetic circulation model with ventricular fibrillation. After implantation, these goats were placed in a cage and extubated after waking. All hemodynamic parameters with the natural circulation without biventricular bypass pumping, and the artificial circulation with biventricular bypass pumping under ventricular fibrillation were recorded under awake conditions. By the use of a non linear mathematical technique, the arterial blood pressure waveform was embedded into a four dimensional phase space and projected into three dimensional phase space. The Lyapunov numeric method is used as an adjunct to the graphic analysis of the state space. A phase portrait of the attractor showed a high dimension complex structure, with three dimensional solid torus suggesting deterministic chaos during natural circulation. However, a simple attractor, such as a limit cycle attractor, was observed during artificial circulation. Positive Lyapunov exponents during artificial circulation suggest the lower dimensional chaotic system. Thus, hemodynamic parameters during prosthetic circulation must be carefully controlled when unexpected stimuli are fed from outside.

A mobile communications system for home-visit medical services: The Electronic Doctor's Bag

In the present study, “Electronic Doctors Bag” which is a tele-healthcare tool for home-visit medical service using the mobile communications environment has been proposed and evaluated by preliminary experiments. It was shown that its basic function was sufficiently evaluated by a few doctors and nurses but further improvement in portability and operability is required on the basis of much more opinions of medical and nursing professionals.

Successful closure of coronary-bronchial artery fistula with vein graft-coated stent.

A coronary‐bronchial fistula and aneurysmal dilatation of the proximal part of the fistula was successfully closed using an autologous vein graft‐coated stent (Palmaz‐Schatz stent). This is the first report that demonstrates the feasibility of the vein‐coated stent for the treatment of congenital disease. Cathet. Cardiovasc. Intervent. 46:214–217, 1999.

An electromagnetically driven univalved artificial heart

A wide variety of clinical blood pumps including powering systems have been developed and evaluated for totally implantable support systems [1–6]. However, there are still several serious problems, such as thromboembolic episodes, size, and weight, affecting prolonged survival of a total system inside the body.

Arterial Resonance Inferred from Analysis of Arterial Impedance

At an irregular point in an artery, a pulse wave is reflected, generating a characteristic impedance. An arterial branch is a major origin of such reflection waves. It may be possible to make an artery resonate by using an artificial heart which is carefully controlled to generate the appropriate frequency for the target point. In this report, arterial impedance was studied in animal experiments. Total cardiopulmonary bypasses were performed using a vibrating flow pump generating a 10–40-Hz oscillating blood flow. It was found that the value of arterial impedance at around 30 Hz was increased compared with that at other driving frequencies. Blood flow distribution was also changed at 30 Hz; the left common carotid arterial blood flow rate underwent a relative increase with a 30-Hz oscillating blood flow. These results indicate that 30 Hz is a point of significance in determining the frequency characteristics of this artery. It is postulated that resonance of the artery caused a reflection wave from the aortic arch at 30 Hz. The power generated by pulsatile flow is the product of mean flow and amplitude. It may be important to study the hemodynamics from the viewpoint of alternating current theory, i.e., considering arterial impedance, as well as direct current theory. Arterial resonance may become an important factor in the management of the artificial circulation of blood.

Fractal Dimension Analysis of Chaos in Hemodynamics with Artificial Heart

To analyze the hemodynamic parameters in prosthetic circulation as a complete entity, not as a decomposed entity, non-linear mathematical techniques, including chaos and fractal theory, were utilized. Two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses (BVB) in chronic animal experiments in four healthy adult goats. For the comparison between the natural and prosthetic circulation, the BVB type complete prosthetic circulation model with ventricular fibrillation was adopted. All hemodynamic parameters with natural circulation without BVB pumping and artificial circulation were recorded under awake conditions, and calculated with a computer system. By the use of a non-linear mathematical technique, arterial blood pressure waveform was embedded into the return map by the beat-to-beat variability, and fractal dimension analysis was performed to analyze the reconstructed attractor. By the use of the box-counting method, fractal dimension analysis of the hemodynamics was performed. The return map of the hemodynamics during natural and artificial circulation showed the characteristics of lower dimensional fractal. The fractal time series data were suggested to have robusticity and error resistance. Thus, our results suggest that the circulatory regulatory system with the artificial heart may have these desirable characteristics.

Fractal Dimension Analysis of Heart Rate Variability with Left Ventricular Assist Device

We analyzed heart rate variability by nonlinear mathematics, including fractal theory, to evaluate the hemodynamic stability of left ventricular assistance. A left ventricular assist device (LVAD) was implanted from the left atrium to the descending aorta in four long-term experiments using healthy adult goats. After the implantation procedure, these goats were placed in a cage, and then extubated after the anesthesia was terminated. All time-series data were recorded with the animals awake. The LVAD was driven in internal mode (INT) at a rate of 50–60bpm, counterpulsation mode (CP), and copulsation mode (CoP). Electrocardiograms were recorded. To assess the heart rate variability with the LVAD, we calculated the fractal dimension by the box-counting method. During left ventricular assistance, fractal dimensions were decreased. This result suggests that the hemodynamics during LVAD use have decreased fractal characteristics. A system which has fractal structures is said to have the characteristics of stability when stimuli are fed from outside. During LVAD use, we must carefully control the hemodynamic parameters to compensate for any unexpected stimuli received from outside.

Sympathetic Nerve Adjustment to Artificial Circulation

To analyze the dynamical behavior of the autonomic nervous system while being driven by an artificial heart, sympathetic nerve discharges were analyzed by the use of nonlinear mathematics, including chaos and fractal theory. For the comparison of the natural and artificial circulation, a biventricular bypass type, total artificial circulation model was adopted under ventricular fibrillation in short-term animal experiments on four healthy mongrel dogs. After the implantation of a biventricular assist pneumatic pump, bipolar stainless steel bipolar electrodes were attached to the left renal sympathetic nerve via a retroperitoneal approach, to record the sympathetic nerve discharges. After amplifying the nerve activity with a preamplifier, the sympathetic discharges were further amplified with a main amplifier and integrated with a resistance-capacitance (R-C) integrator (time constant 0.1s). After control natural-circulation data were recorded without biventricular assistance, ventricular fibrillation was induced electrically, and the biventricular bypass pneumatic pump was started, constituting the total artificial circulation model. Driving parameters for the bypass pumps were manually controlled to maintain the hemodynamic parameters within the normal range. Time-series data of the hemodynamics and sympathetic nerve discharges were recorded in the data recorder and calculated in a personal computer system (PC9801RA) through an analog-digital (A-D) converter. Even during artificial heart circulation, the reconstructed attractor of the sympathetic discharges in the phase space appeared to be a strange attractor, which is a feature of deterministic chaos. However, the Kolomosov-Sinai (KS) entropy of the reconstructed attractor decreased during artificial circulation, suggesting changes in the nonlinear dynamics in the autonomic nervous system. Various values of the KS entropy were observed according to the various drive rates of the artificial heart. Our results suggest that there is chaotic itineracy in the autonomic nervous system according to variations in the natural and artificial circulation, and artificial heart drive rate. These results suggest sympathetic nerve adjustments of the circulatory regulatory system in response to the artificial heart. It becomes possible to analyze the information-processing mechanism of the central nervous system by such an open loop experiment using an artificial organ. This mechanism is a focus of attention in the scientific community. We expect that this paper will contribute to understanding this field.

Flow visualization of ventricular assist device using tracer method.

The ventricular assist device (VAD) should supply the wide range of the flow assistance according to the cardiac requirement after the failing natuaral heart. The flow behavior within our different several types of VADs had been analized with the numerical method based on the flow visualization technique. In this study, it was observed that the stagnation in which the thrombus would be generated was affected mainly by the contour of VAD. According to the results of the flow. characteristics within VADs, the contour of the junctions between the sac and the inflow and outflow tracts were improved to the smooth configuration which enhanced the rotating flow in the diastole and minimized the stagnant area within the sac. It was concluded that the flow visualization furnished the very useful information on the development of the VAD.