Makoto Yoshizawa

Real-time cardiac output estimation of the circulatory system under left ventricular assistance

A method for indirect and real-time estimation of the cardiac output of the circulatory system supported by the left ventricular assist device (LVAD) is proposed. This method has low invasiveness and is useful for clinical applications of the LVAD since it needs only two measurements: the rate of blood outflow from the LVAD and the aortic pressure. The method is based on a system identification technique for the time-series model of the cardiovascular system and requires less computational time than other methods with similar estimation accuracy. Hence, the method could be implemented in a personal computer system and realize online, real-time estimation of the instantaneous outflow rate of the natural heart. Results obtained in vitro using a mock circulatory system and in vivo using an adult goat show that the method can yield a fairly high correlation coefficient between the true stroke volume of the natural heart and its estimate of more than 0.99 (in vitro) or 0.95 (in vivo). The estimation method thus appears suitable for clinical use.<<ETX>>

A frequency domain hypothesis for human postural control characteristics (visual feedback)

Experiments performed to determine the effect of filtered visual feedback information in the frequency domain on human body sway during quiet standing is described. The three-dimensional visor display system (3D-VD) was used to filter the visual feedback information. A hypothesis is proposed to explain the test subjects postural control characteristics and to estimate the different roles of the visual information used for postural stability in the low and high frequency domains. It is concluded that the hypothesis based on the spatial map in the brain is useful to explain the different roles of the visual feedback information in the frequency domain.<<ETX>>

An automatic monitoring and estimation tool for the cardiovascular dynamics under ventricular assistance

An automatic, on-line and real-time monitoring and estimation tool for the cardiovascular dynamics under pumping of the left ventricular assist device (LVAD) has been developed to unload the operator who has to pay constant attention to the LVAD operation. The tool can detect the presence and origin of accidents happening in the cardiovascular system, the pneumatic drive unit as well as the automatic controller by means of the fuzzy reasoning. The cardiovascular parameters such as peripheral vessel resistance, arterial compliance and cardiac output are estimated by means of a time series model. In vivo experiment using an adult goat revealed that the proposed system successfully worked during withdrawal of blood.

Simulation study on a control strategy of total artificial heart based on vascular conductance

A new control method of the total artiflcial heart (TAH) proposed by Y.Abe[l] in which the cardiac output of TAH t adjusted on the bank of the peripheral V M C U ~ R ~ conductance han been examined with digital computcr simulation. As a result, its control theoretical aspects and direction of improvement have been revealed. peripheral vascular resist. INTRODUCTION The typical and traditional control strategy of the artificial heart is to regulate the atrial pressure, the aortic pressure or the cardiac output so as to keep each value constant. For example, a control method based on FrankStarling’s law aims at keeping the atrid pressure constant. In application of such a method, however, we have never had any standard criterion to decide its reference value to be approached. To avoid this problem, Abe,el af . [ l ] has proposed the method in which the cardiac output of the total artificial heart is adjusted so as to depend on the reciprocal of tbe peripheral vascular resistance, i.e., the peripheral vascular conductance. Abe called this method “1/R control method”. The peripheral vascular conductance can be changed by the autonomic nemous system in vivo. In such a method, hence, the cardiac output may be adjusted by the recipient himself and we don’t have to decide any reference input to be given outside his body. However, Abe’s 1/R control method has never been examined from the viewpoint of control engineering. In the present paper, the examination of Abe’s l /R control strategy is reported using digital computer simulation. DIGITAL SIMULATION Electrical Circuit Model of Cardiovascular System 0-7803-1377-1/93

A Hypothesis That Explains The Human Postural Control Characteristics

3.00 01993 IEEE 913 L CRV CPA 111 CPV CLA LV Figure 1: Electrical circuit model. Fig.1 shows our digital simulator based on an electrical circuit model to mimic the cardiovascular system. To extract only the typical feature of dynamic behavior of Abe’s control method, the model was made as simple as possible. For example, all nonlinear elements and systemic shunt vessel were omitted. Dynamic Behavior of Cardiovascular System By use of this simulator, the dynamic behavior of the circulatory system under Abe’s control strategy could be obtained as shown in Fig.2. Abe’s method is represented by where Rg’ [ml/(mmHgs)]: peripheral vascular conducHRk+I [/min]: heart rate a t (k + 1)-th beat, AOPk [mmHg]: aortic pressure at k-th beat, m k [mmHg]: aortic pressure through a low [mmHg]: set point of right atrial pressure, tance, pass digital filter at k-th beat,

New Artificial Heart Control Method from the Neurophysiological Point of View

To investigate the role of the visual feedback information in the frequency domain, the frequency component included in the visual feedback information has been filtered and the effect of the filtered information on the human body sway during quiet standing has been analyzed. A hypothesis has been proposed to explain the test subjects postural control characteristics and to estimate the different roles of the visual information used for postural stability in the low and the high frequency domains.

Adaptive estimation of impedance cardiographic signals

In order to determine optimal drive conditions for the total artificial heart (TAH) from the neurophysiological point of view, power spectral analysis of the hemodynamic parameters in animals chronically implanted with TAH was performed to analyze the rhythmical fluctuations that reflect the operation of cardiovascular regulatory systems. Two ventricular assist devices were implanted as total biventricular bypasses (BVB) in chronic animal experiments with adult goats. Natural hearts were then electrically fibril-lated to constitute the BVB type of TAH model for comparison of the circulation in animals with a natural heart and those with a TAH. Mayer waves and respiratory waves were clearly observed in the arterial pressure of the TAH animal, these fluctuations being significantly influenced by the TAH driving conditions. These results suggest that fluctuations in the hemodynamics of animals with TAH can provide information for TAH control systems.

Rhythmical fluctuations of the arterial blood pressure in animal with total artificial heart

An adaptive filter to estimate the deterministic component of the impedance cardiographic signal is presented. This filter removes the noise uncorrelated with the impedance cardiographic signal time-locked to the R-R interval of ECG, using the least mean square (LMS) algorithm. The basic theory and some simulations are presented to verify the the filter performance.<<ETX>>

Chaotic hemodynamics during oscillated blood Flow

In order to investigate the origin of the fluctuations in hemodynamic parameters, total artificial heart (TAH) replacement was performed in chronic animal experiments using adult goats. Two ventricular assist devices were implanted as total biventricular bypass (BVB) and natural heart was electrically fibrillated. The results suggest that fluctuations in the hemodynamics of the TAH animal are originated from the periodicity of the peripheral and pulmonary vascular resistance.