Biomedical subjects

Y Sankai

Publications and source records attributed to Y Sankai.

9 recordsLinked to original sources

PubMed2004

Effect of left ventricular assist device on circulatory autonomic nervous activity.

PURPOSE: For evaluation of the autonomic nervous system (ANS) activity of patients with mechanical circulatory support including LVAD, IABP and PCPS, arterial pressure variability (APV) was examined. APV is the power density values of pressure signals. High frequency (0.15 to 0.4 Hz) and low frequency (0.04 to 0.15 Hz) components of APV are regarded as a function of the autonomic nervous system. METHODS: Arterial pressure signals were acquired every 2 hours at 100 Hz for 6 minutes. Power spectral analysis was carried out, and APV was observed in 18 patients with IABP and/or PCPS. APV was also observed in 3 patients with LVADs (Xemex, Zeon Medical, Japan) before their discharge from ICU for transfer to another hospital for cardiac transplantation. RESULTS: Although the value gradually increased in 18 patients with IABP and/or PCPS, sustained low values of LFAnorm of APV in 6 patients were related to prolonged mechanical support, and 4 patients among them died consequently. The normalized power spectral component with low frequency (LFAnorm) was maintained at relatively high values in 3 patients with LVADs. CONCLUSION: The study results suggest that power spectral analysis of systemic arterial pressure offers a reasonable means for the evaluation of the severity of patient cardiovascular condition and for the prediction of clinical outcome. It also suggested that LVAD support exerts a favorable effect on ANS in patients with severe heart failure before cardiac transplantation.

Adult↗

PubMed2001

The estimation of cardiac function from the rotary blood pump.

The rotary blood pump is implanted as a bridge to cardiac transplantation. Mechanical, histological, and biochemical improvements have been described in patients after implantation of left ventricular assist devices (LVADs). Thus, the rotary blood pump might be used as a bridge to recovery of myocardial function. However, unlike a pulsatile pump, the rotary blood pump cannot be stopped to estimate cardiac function: if the rotary blood pump stops, backflow will occur. In this study, a new method that can estimate cardiac function without pump stop was examined. Six pigs were the subjects of this acute study. The pump was implanted as an LVAD: the inlet cannula was inserted into the left ventricle, and the outlet cannula was inserted into the ascending aorta. The motor speed was regulated at a pump flow rate of 0 L/min at diastolic phase. Then, the relationship between the dp/dt of left ventricular pressure and external stroke work of actuator was examined. This method was studied at normal, hyperdynamic, and heart-failure conditions. There was a high positive correlation between the dp/dt of left ventricular pressure and external stroke work of actuator. This method is useful and simple to estimate cardiac function without pump stop.

Animals↗

PubMed2000

Estimation of pump flow rate and abnormal condition of implantable rotary blood pumps during long-term in vivo study.

The control system for an implantable rotary blood pump is not clearly defined. A detection system is considered to be necessary for pump flow monitoring and abnormal conditions such as back flow or a sucking phenomenon where the septum or left ventricle wall is sucked into the cannula, etc. The ultrasound flowmeter is durable and reliable but the control system should not be totally dependent on the flowmeter. If the flowmeter breaks, the rotary blood pumps have no control mechanism. Therefore, the authors suggest controlling the pumps by an intrinsic parameter. One left ventricular assist device (LVAD) calf model was studied where the flow rate and waveform of the pump flow proved to identify the sucking phenomenon. Thus, the pump flow rate was calculated from the required power, motor speed, and heart rate. The value of the coefficient of determination (R2) between the measured and estimated pump flow rate was 0.796. To estimate this abnormal phenomenon, 2 methods were evaluated. One method was the total pressure head in which the pump flow rate and motor speed were estimated. During normal conditions the total pressure head is 79.5 +/- 7.0 mm Hg whereas in the abnormal condition, it is 180.0 +/- 2.8 mm Hg. There was a statistical difference (p < 0.01). Another method is using a current waveform. There is an association between the current and pump flow waves. The current was differentiated and squared to calculate the power of the differentiated current. The normal range of this value was 0.025 +/- 0.029; the abnormal condition was 11.25 +/- 15.13. There was a statistical difference (p < 0.01). The predicted flow estimation method and a sucking detection method were available from intrinsic parameters of the pump and need no sensors. These 2 methods are simple, yet effective and reliable control methods for a rotary blood pump.

Animals↗

PubMed2000

Control system for an implantable rotary blood pump.

Rotary blood pumps can be used for long-term left ventricular assist devices. These pumps have several advantages over the conventional pulsatile pumps including smaller size, higher efficiency, and simple design and construction. However, one of the difficulties associated with the rotary blood pump is the proper control method to maintain an optimum flow rate in different physiological conditions. The rotary blood pump can be controlled by two methods. The first is to utilize the measured pump flow rate from its servo signal. The second is to detect and avoid abnormal pumping conditions such as; back flow and sudden increase in the pressure head. This abnormal situation typically occurs from excessive suction of blood when there is a functional or mechanical occlusion in the inflow cannula. The ultrasound flow meter is durable and reliable but it is difficult to continually monitor the blood flow rate of an implantable pump. Therefore, another method is needed instead of the continuous flow monitoring. One chronic calf having an LVAD was subjected for the development of this control system. This calf survived more than 6 months. Voltage, current, motor speed, heart rate and the pump flow rate were recorded and stored at 30-min intervals in a computer. Utilizing these parameters, attempts were made (1) to achieve indirect flow assessments and (2) to reveal abnormal operating parameters of the centrifugal pump (1). Indirect flow measurement, the predicted pump flow rate was calculated from these pump derived parameters (required power, motor speed and heart rate). The value of the coefficient of determination (R) between the measured and estimated pump flow rate was 0.796. (2) Abnormal operating indicator, there was an association between the required current and pump flow waves. The current was differentiated, and then calculated to the power of the differentiated current. The normal range of this value was 0.02+/-0.54. In abnormal conditions, this abnormal operating indicator increased 500 times. The predicted flow estimation method and abnormal operating indicator were available from intrinsic operating parameters of the pump and need no sensors. These two methods were simple, yet they are possibly effective and reliable servo control methods for a rotary blood pump.

Animals↗

PubMed1999

Long-term in vivo left ventricular assist device study for 284 days with Gyro PI pump.

A totally implantable centrifugal artificial heart has been developed. The plastic prototype, the Gyro PI 601, passed 2 day hemodynamic tests as a functional total artificial heart (TAH), 2 week screening tests for anti-thrombogenecity, and a 1 month system feasibility study. Based upon these results, a metallic prototype, the Gyro PI 700 series, was subjected to long-term in vivo left ventricular assist device (LVAD) studies of over 1 month. The Gyro PI 700 series has the same inner dimension and same characteristics of the Gyro PI 601 such as an eccentric inlet port, a double pivot bearing system, and a magnet coupling system. The PI metallic pump is also driven with the Vienna DC brushless motor actuator like the PI 601. The pump-actuator package was implanted in 3 calves in the preperitoneal space, bypassing from the left ventricular (LV) apex to the descending aorta. Case 1 achieved a 284 day survival. Case 2 was euthanized early at 72 postoperative days as a result of the functional obstruction of the inlet port due to the excessive growth of the calf. There was no blood clot inside the pumps of either case. Case 3 is on-going (22 days on July 24, 1998). During these periods, all cases showed no physiological abnormalities. In conclusion, the PI 700 series pump has excellent results as a long-term implantable LVAD.

Animals↗

PubMedDate not supplied

Operating point control system for a continuous flow artificial heart: in vitro study.

We proposed and developed a practical and effective servo control system for rotary blood pumps. A rotary blood pump for assisting the failing natural heart should be operated only in physiologically acceptable conditions. The operation of a rotary blood pump is based on the rotational speed of the impeller and pressure head. If the pump flow and the pressure head are set within an acceptable range, the driving condition is deemed normal condition, and this control system maintains the preset operating point by applying proportional and detective control (PD control). If the pump flow or pressure head is outside the acceptable range, the driving condition is determined to be abnormal condition, and this system operates the pump in a recovery fashion. If the driving condition is kept under abnormal conditions of sudden decrease of the flow, the condition is termed a suction condition. The controller releases the pump from the suction condition and later returns it to the normal condition. In this study, we evaluated these servo control modes of the centrifugal pump and confirmed whether the performance of this proposed operating point control system was practical.

Algorithms↗

PubMedDate not supplied

Muscle type-specific response of PGC-1 alpha and oxidative enzymes during voluntary wheel running in mouse skeletal muscle.

AIM: It is generally accepted that endurance exercise increases the expression of peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), which governs the expression of oxidative metabolic enzymes. A previous report demonstrated that the regulation of mitochondrial protein expression in skeletal muscles in response to cold exposure depends on muscle fibre type. Cold exposure and endurance exercise are both metabolic challenges that require adjustments in mitochondrial energy metabolism, we hypothesized that the exercise-induced increase in oxidative enzymes and PGC-1alpha expression is higher in fast-type than in slow-type muscle. METHODS: Female ICR mice were individually housed in cages equipped with running wheel for 1, 2, 4, 6 or 8 weeks. The soleus, plantaris (PLA) and tibialis anterior (TA) muscles were then prepared from each mouse. The expression levels of PGC-1alpha, mitochondrial proteins and GLUT4 were evaluated by Western blotting. RESULTS: The expression level of PGC-1alpha was increased only in the PLA muscle. Furthermore, the expression levels of all mitochondrial proteins and GLUT4 in the PLA muscle were increased. In the TA muscle, although there was no increase in PGC-1alpha expression, the expression levels of mitochondrial proteins and GLUT4 were increased. CONCLUSIONS: These results suggest that muscle type-specific responses occur during endurance exercise, and that the increase in PGC-1alpha expression is not the only factor that promotes oxidative capacity as a result of endurance exercise.

Animals↗

PubMedDate not supplied

Method of noninvasive and continuous hemolysis/thrombogenesis measurement by laser photometry during artificial heart development.

The purpose of this research is to propose and develop a method to measure hemolysis and thrombogenesis non invasively and continuously to aid in development of an artificial heart. Generally, the optical absorption rate of hemoglobin is influenced by oxygen saturation except at the isosbestic point, which is not influenced by oxygen saturation. The authors, therefore, used an 805 nm laser diode, an optical spectrum analyzer to obtain greater accuracy. An experimental blood circuit system was constructed using a Bio-Pump, Tygon tubing, a soft shell reservoir, and an optical measurement system. Experimental settings for monitoring hemolysis were as follows; blood volume 200 ml, blood flow 6 L/min, and afterload 200 mmHg. Blood was sampled six times (0, 30, 60, 120, 180, and 240 min), and hemolysis in each sampled was measured using a colorimetric method. Comparing continuous laser measurement data with the sample data, an adequate correlation is obtained, proving that the dynamic trend of hemolysis could be continuously measured. Furthermore, to analyze the process of thrombogenesis, simple experiments were performed using blood neutralized by protamine. As a result, the authors could see the process of thrombogenesis as it occurred and could confirm that this method is able to dynamically detect hemolysis and thrombogenesis.

Biomedical Engineering↗

PubMedDate not supplied

Species differences in erythrocyte mechanical fragility: comparison of human, bovine, and ovine cells.

The erythrocyte destruction rate under constant shear stress was measured to clarify species differences in red blood cell (RBC) mechanical fragility between human, bovine, and ovine cells. Blood was collected from healthy donors by venipuncture. RBC age fractionation was performed by high speed centrifugation (20 min at 12,000 g). Relatively young, middle, and old age RBCs was suspended in Dulbecco's phosphate buffered saline to adjust the hematocrit to 35%. Uniform shear stress was applied to each sample contained in a concavo-convex Couette flow testing machine. Young and old aged samples were exposed to 300 dyne-sec-cm2 for 0 and 15 min. Middle aged samples were exposed to 300 dyne-sec-cm2 for 0, 5, 10 and 15 min. Liberated hemoglobin was estimated by tetramethylbenzidine colorimetric measurement and the erythrocyte destruction rate was calculated. Older samples had a higher hemolysis rate than younger samples in every species. The destruction under constant shear stress is approximately linear in time. Mechanical fragility of ovine and bovine RBCs was 1.8 and 0.5 times as large as human RBCs, respectively. These values could serve as universal standards when extrapolating animal hemolysis data for any blood pump to predict its safety and biocompatibility in human clinical trials.

Animals↗