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Shin-ichi Nitta

Publications and source records attributed to Shin-ichi Nitta.

13 recordsLinked to original sources
PubMed2004

Open-loop analysis of transfer characteristics from blood pressure to heart rate using an effectively total artificial heart.

It is desirable for the dynamic behavior of the drive rate of the artificial heart to be as similar as possible to that of the recipient's heart rate (HR) before implantation. This requires a model which can simulate the behavior of HR on the basis of only the information measured with the limited number of approvable implanted sensors. This article provides a linear time series model for explaining the behavior of HR only with aortic pressure and right atrial pressure. This could be obtained from open-loop analysis using a total artificial heart, which was introduced for measuring HR in vivo and for eliminating its effect on blood pressure. The model was identified in a goat equipped with a special biventricular assist device called the effectively total artificial heart (ETAH). The ETAH was introduced to make an open loop and awake situation in the animal with almost intact autonomic nerves, which could enhance the accuracy and reliability of the identification of the model. The adequacy of the proposed model was ascertained in several data sets measured in two goats, which were different from the data set used for identification. Most of the mean estimation errors were less than 3 beats/min and auto-correlation analysis showed approvable statistical appropriateness. However, it was clarified through comparison with the 1/R control method that the proposed model has a few problems still to be solved before its future implementation as an automatic controller of the TAH.

Animals↗
PubMed2003

Can personality traits predict pathological responses to audiovisual stimulation?

The "Pockemon shock" is the most famous accident in the history of the broadcasting industry in Japan. Based on the experiences of this unfortunate accident from famous animation program "Pocket Monster", this study focused on the psychology and psychosomatics of the patients. A head-mounted display was used as the three-dimensional image presentation device and "Descent", a free software shooting game, was used as the software. Ten healthy adult male volunteers were used in this experiment after obtaining their informed consent. The oxygen metabolic change in the anterior lobe of the brain was measured by near infrared spectroscopy and recorded on an electrocardiogram. The mental scaling tendency of the object was analyzed using the type A behavior pattern and the hostility scaling. The Cook and Medley hostility (HO) scale from the Minnesota multiphasic personality inventory (MMPI) was also used in this experiment. From this scaling methodology, the paranoid scale, cynicism scale, lie scale, social support quality and social support quantity were calculated. All measured time series data were kept in the normal range, and no fatal arrhythmia or epilepsy were observed during experiments. In some cases, the brain oxygen metabolism may completely differ for the objects of Type A and Type B behavior patterns. On the whole, correlation did not become significant in type A scaling and hostility scaling. In a comparison of the percent changes of the HF in HRV with lie scaling, significant negative correlation was observed. The social support quantity was calculated from Cook and Medley, and significant negative correlations were observed with percent changes of LF/HF in HRV. The lie scale and social support quantity are opposite scaling. The sympathetic nervous system and parasympathetic nervous system have an opposite function also. Therefore, our results showed an interesting phenomenon, when considering the relationship between the autonomic function and the pathophysiological reaction to the audiovisual stimulations. As for the photo sensitive epilepsy, it was reported to be only 5-10% for all patients. Therefore, 90% or more of the cause could not be determined in patients who started a morbid response. The results in this study suggest that the autonomic function was connected to the mental tendency of the objects. By examining such directivity, it is expected that subjects, which show morbid reaction to an audiovisual stimulation, can be screened beforehand.

Acoustic Stimulation↗
PubMed2003

Influence of tissue preparation on the acoustic properties of tissue sections at high frequencies.

The purpose of the present study was to clarify the influence of tissue preparation on the high-frequency acoustic properties by comparing the acoustic properties of the formalin-fixed, paraffin-embedded, deparaffinized sections and formalin-fixed, frozen sections for two types of fat-containing renal cancer and fat-free renal oncocytoma using a SAM. There was no significant difference for the sound speed among the clear cell, granular cell renal cancer and oncocytoma in either groups, but the attenuation constant was significantly higher for the frozen than for that of the paraffin section in fat-containing renal cancer. In fat-free oncocytoma, there was no significant difference for the attenuation constant in either group. The data suggest that the fat component, which had been eluted by paraffinization, is stored and the true acoustic properties of the tissue can be measured in frozen section.

Adenocarcinoma, Clear Cell↗
PubMed2003

In vivo test of pressure head and flow rate estimation in a continuous-flow artificial heart.

To avoid using sensors with low biocompatibility and low durability in implantable total artificial heart (TAH) systems, the authors previously proposed a new method for estimating instantaneous values of flow rate and pressure head on the basis of voltage, current, and rotational speed in a motor driven centrifugal pump. The previous in vitro experiments showed that the proposed estimator could automatically compensate for the effect of the change in blood viscosity on the estimation accuracy by employing two kinds of autoregressive exogenous models. In this study, validity and reliability of this estimation method were ascertained in an acute animal experiment. In the experiment, two centrifugal blood pumps were implanted into an adult goat as a total artificial heart. Results of estimation were compared with true values when blood viscosity was changed by injecting physiological saline. The results indicated that the system could successfully estimate pressure head by compensating the change of viscosity, although the estimation accuracy of the in vivo estimation was not so high as that of the previous in vitro tests.

Animals↗
PubMed2003

Recent progress in artificial organ research at Tohoku University.

Tohoku University has developed various artificial organs over the last 30 years. Pneumatic driven ventricular assist devices with a silicone ball valve have been designed by the flow visualization method, and clinical trials have been performed in Tohoku University Hospital. On the basis of these developments, a pneumatic driven total artificial heart has been developed and an animal experimental evaluation was conducted. The development of artificial organs in Tohoku University has now progressed to the totally implantable type using the transcutaneous energy transmission system with amorphous fibers for magnetic shielding. Examples of implantable systems include a vibrating flow pump for ventricular assist device, an artificial myocardium by the use of shape memory alloy with Peltier elements, and an artificial sphincter for patients with a stoma. An automatic control system for artificial organs had been developed for the ventricular assist devices including a rotary blood pump to avoid suction and to maintain left and right heart balance. Based upon the technology of automatic control algorithm, a new diagnostic tool for evaluating autonomic nerve function has been developed as a branch of artificial organ research and this new machine has been tested in Tohoku University Hospital. Tohoku University is following a variety of approaches aimed at innovation in artificial organs and medical engineering fields.

Academic Medical Centers↗
PubMed2003

Chaos attractors of ventricular elastance to evaluate cardiac performance.

Quantitative evaluation of cardiac function is very important in the clinical application of a ventricular assist device. This article reports a new evaluating method of E max, which is the most reliable parameter to evaluate cardiac function. Fluctuation in the E max time series data was evaluated by the nonlinear mathematical analyzing method including chaos and fractal theory. Experimental goats were anesthetized with halothane inhalation, and left ventricular volume and pressure were measured with other hemodynamic parameters to evaluate E max during various drug administrations. E max was evaluated by two methods. One was the conventional pressure volume loop evaluation and the other was the parameter optimization method without left ventricular volume data. As a result, E max evaluated by the parameter optimization method correlated well with the E max with conventional PV curve. Furthermore, interesting results were obtained. There were rhythmical fluctuations in the E max time series data. By the methodology of Takens, E max time series data was embedded into the phase space and a strange attractor was observed. These results may be important when considering E max evaluation during left ventricular assistance.

Animals↗
PubMed2003

Outflow control for avoiding atrial suction in a continuous flow total artificial heart.

Continuous flow blood pumps, such as axial flow and centrifugal pumps, have been gaining interest as circulatory devices for total artificial hearts (TAHs) because of their smaller size and simpler structure compared to pulsatile pumps. However, continuous flow pumps are more prone to atrial wall suction than pulsatile pumps are. Sudden increases in flow rate to meet changes in physiological demand, especially in the left pump, often cause atrial wall suction. In this study, a control algorithm to prevent atrial wall suction from occurring in the left atrium by controlling the rotational speed of the right pump, instead of reducing the cardiac output of the left pump, was developed and investigated. The method was tested in a mock circulatory system and in acute animal experiments with adult goats. Two centrifugal pumps were used to totally replace the circulatory function of the natural heart. The cardiac output of each pump was determined independently by a control algorithm running on a computer connected through a serial interface to the pump driving units. Results showed that left atrial wall suction could be prevented using this method, and that the method could be performed simultaneously with physiological control of the artificial heart.

Algorithms↗
PubMed2003

Computational flow visualization in vibrating flow pump type artificial heart by unstructured grid.

Computational flow visualization in the casing of vibrating flow pump (VFP) was made for various conditions based on the novel techniques of fluid dynamics. VFP type artificial heart can generate the oscillated flow and can be applied to the left ventricular assist device. Flow pattern of blood in an artificial heart is closely connected to mechanical performance and serious biomechanical problems such as hemolysis and blood coagulation. To effectively design the VFP for a left ventricular assist device, the numerical codes for solving Navier-Stokes equations were developed for three-dimensional blood flow based on the finite volume method. Furthermore, the simulation techniques based on the artificial compressibility method and the unstructured grid were also developed here. The numerical calculations were based on the precise configurations and the flow conditions of the prototype device. From the viewpoint of computational fluid dynamics (CFD), the detailed discussion of flow patterns in the casing of VFP, which were closely connected with hemolysis and blood coagulation, was made and the computational results were visualized by the use of the recent technique of computational graphics. Some useful design data of VFP were presented.

Blood Flow Velocity↗
PubMed2002

Non-linear dynamic analysis of hemodynamic parameters in an undulation type artificial heart system.

Undulation pump total artificial heart (UPTAH) is a unique total artificial heart implant (TAH) using an undulation pump that is a continuous blood flow pump. To evaluate the autonomic nerve function mediating the circulation system, we analyzed the hemodynamic parameters during animal experiments with UPTAH using the non-linear mathematical analyzing technique, including chaos and fractal theory. Adult female goats were used for the implantation of UPTAH. The natural heart was replaced with UPTAH under extra-corporal circulation. The conductance- and arterial pressure-based control method (1/R control) was applied on the 5th to 7th post-operative day as the influences of the cardiopulmonary bypass circulation were diagnosed to be terminated. Hemodynamic parameters were recorded on the data recorder, and non-linear mathematical analysis was performed. For the quantitative evaluation of the strange attractor, which was the characteristics of the deterministic chaos, the fractal dimension analysis was carried out. As a result, hemodynamic parameters fluctuated on the time axis and showed fractal characteristics, which were thought to be the characteristics of the deterministic chaos. The reconstructed attractor of the hemodynamics showed various behaviors according to changes in the situation of the goats. These results suggest that non-linear dynamical analysis might be useful in monitoring the circulatory regulatory system in artificial heart circulation.

Animals↗
PubMed2002

Non-linear dynamic analysis of hemodynamic behavior during virtual reality immersion.

Several years ago, a famous accident occurred in Japan. Hundreds of children, who were watching a cartoon on television, suddenly complained of spasms and vertigo, and were taken to hospital. In this study, the autonomic nervous system was evaluated during audiovisual stimulation with three dimensional Virtual Reality (VR) imaging. In our previous studies, we designed the diagnosis machine for an autonomic function using multi-parameters, including electrocardiography, arterial blood pressure, respiration and stroke volume as detected by ultrasonic cardiography. Healthy adult volunteers were used in this experiment with their satisfactory informed consent. The three-dimensional content for VR included dinosaur images in a pre-historic scene. The content was projected on a wide screen and volunteers watched an audiovisual screen for about 20 minutes and the 3-D and 2-D images were compared. There was no significant arrhythmia during experiments in both images. No significant alteration was observed in the quantified hemodynamic data during the experiment. Spectral analysis was performed to evaluate the heart rate variability (HRV) during the experiment. LF, HF and LF/HF of HRV were calculated. However, there were no significant changes during the experiment. Significant change was observed in the fractal dimension of the stroke volume during 2-D and 3-D image VR immersion. Our results suggest that a significant response was observed in the autonomic function according to the 2-D or 3-D images. Our study, which aims at safe audiovisual stimulating equipment, must be developed.

Acoustic Stimulation↗
PubMedDate not supplied

Sensorless estimation of pressure head and flow of a continuous flow artificial heart based on input power and rotational speed.

The present study has proposed a new method for estimating the pressure head (P(t)[mm Hg]) and flow (Q(t)[L/min]) of a centrifugal pump on the basis of voltage (V(t)[V]), current (I(t)[A]), and rotational speed (N(t)[k(rpm)]) of the DC motor for a pump without any additional sensors. In the proposed estimation method, two auto-regressive exogenous (ARX) models are employed. One ARX model has an output, P(t) or Q(t), and three inputs, VI(t) = V(t)I(t) and N(t) and the steady state gain (K) of the system from VI(t) to N(t). It can be assumed that K may include the information on viscosity of blood. The coefficient parameters of this ARX model are identified in an off-line fashion before implantation of the pump. After implantation, P(t) or Q(t) is estimated by the same ARX model with the already identified parameters. The other ARX model is used to identify Kon the basis of VI(t) and N(t) in an on-line fashion every time the viscosity of blood may change. In the experiment, a mock circulatory system consisting of a centrifugal pump and a reservoir with 37% glycerin or water was employed. The root mean square error between measured Q(t) and its estimate obtained from the proposed method was 1.66L/min. On the other hand, a different method based on a single ARX model with inputs of VI(t) and N(t), but without the additional input of K, yielded the corresponding estimation error of 2.22L/min. This means that the proposed method can reduce its estimation error by about 25% in comparison with a method that cannot cope with the change in blood viscosity.

Blood Flow Velocity↗
PubMedDate not supplied

Recording vagal nerve activity for the control of an artificial heart system.

Monitoring cardiovascular control system information is important in considering the quality of life (QOL) of patients with artificial hearts. Natural heart circulation is controlled by an autonomic nervous system. Therefore, it is desirable to record autonomic nerve activity for the control of artificial heart systems. We directly recorded vagal nerve activity in long-term animal experiments. Six healthy adult goats were anesthetized with halothane inhalation, and thoracotomy was performed with the fourth rib resection during mechanical ventilation. Arterial blood pressure and right and left atrial pressures were continuously monitored with an inserted catheter. Cardiac output was measured by an electromagnetic flow meter attached to the ascending aorta. After the chest was closed, an incision was made in the left neck, and the left vagal nerve was separated. Stainless steel electrodes were inserted into the vagal nerve and fixed by a plasticizer. After the incision was closed, the goats were transferred to a cage and extubated after waking. Vagal nerve activity was measured using hemodynamic parameters when the animals were awake. Our results show that clear observation of autonomic nerve discharge was made through this experimental system for over 1 month. The tonus of the vagal nerve was significantly altered before body motion with hemodynamic changes, suggesting the possibility of prediction. These results suggest that information from autonomic nerves may help to control implantable artificial hearts or ventricular assist devices.

Animals↗