Hisashi Okubo

Indirect flow rate estimation of the NEDO PI Gyro pump for chronic BVAD experiments.

In totally implantable ventricular assist device systems, measuring flow rate of the pump is necessary to ensure proper operation of the pump in response to the recipient’s condition or pump malfunction. To avoid problems associated with the use of flow probes, several methods for estimating flow rate of a rotary blood pump used as a ventricular assist device have been studied. In the present study, we have performed a chronic animal experiment with two NEDO PI gyro pumps as the biventricular assist device for 63 days to evaluate our estimation method by comparing the estimated flow rate with the measured one every 2 days. Up to 15 days after identification of the parameters, our estimations were accurate. Errors increased during postoperation days 20 to 30. Meanwhile, their correlation coefficient r was higher than 0.9 in all the acquired data, and estimated flow rate could simulate the profile of the measured one.

Ten-year NEDO BVAD development program: Moving forward to the clinical Arena

Since 1995, the Baylor Group has been developing a totally implantable NEDO BVAD system. This 10-year program was completed in March 2005, and preparation for clinical trials is underway. This article summarizes the entire 10-year NEDO program and describes the strategy for clinical trials. The project aimed to achieve: (1) dual centrifugal pumps with the ability of full biventricular support, (2) a compact system implantable into small adults, (3) a totally implantable system with transcutaneous energy transmission system (TETS), (4) a durable system with a lifetime of over 5 years, and (5) a system free of thrombus and with minimal hemolysis. The final goals are to complete preclinical system evaluations and commence the clinical trials in the near future. In vitro studies have demonstrated a pump capacity of over 8.5 l/min and an Index of Hemolysis of <0.004 g/100 l. The pump-bearing life expectancy was over 5 years. To date, eight pumps endured in vivo studies of over 3 months without complications, including thromboembolic events. The in vitro endurance studies of eight pumps are longer than 1 year. There were no mechanical malfunctions or pump failure. A stepwise clinical trial is being planned: Step1, a wearable BVAD/VAD will be clinically studied; Step 2, the BVAD/VAD will be implanted intracorporeally without TETS; and, Step 3, a totally implantable system will be clinically evaluated. The NEDO BVAD system has completed preclinical testing. Clinical trial preparation is underway.

Development of a Clipped Single-bag with Bicarbonate Replacement Fluid to Ensure Proper Mixing

A clipped single-bag for bicarbonate replacement fluid was developed to ensure proper mixing before administering to the patient. Nonmixture can cause imbalances of electrolytes and pH, which is a key problem for the current double-bag type bicarbonate replacement fluid sets. To resolve this problem, this single bag properly mixes the solutions before use. The new bag consists of a clip that is placed in the middle to keep the two solutions separated and sealed. When the caregiver is ready to administer treatment, the bag is simply unfolded and the clip automatically detaches, releasing the fluids. Thereby, the bicarbonate fluids are effectively mixed. An optimal clip size with an outer diameter of 16 mm and thickness of 2 mm was determined using compression tests and drop tests. This bag may be a safer and more effective way to provide proper replacement fluid supply for both hemofiltration and hemodiafiltration.

Evaluation of Flow Rate Estimation Method for Rotary Blood Pump with Chronic Animal Experiment

Rotary blood pumps are expected to be used as an implantable ventricular assist device (VAD). In the VAD system, flow rate is important for monitoring of the state of a recipient and for automatic control to maintain appropriate blood perfusion. To obtain flow rate of the pump without any sensors, we proposed a method of estimating flow rate with supplied power and rotational speed using a time series model. To evaluate the accuracy of the proposed estimation method from the aspect of long-term use, we implanted NEDO PI Gyro pumps in a calf and performed a chronic animal experiment. Flow rate, supplied power and rotational speed were measured until post operation day (POD) 63, and the estimated flow rate was compared with the measured one. We confirmed that waveforms of the measured flow rate was sufficiently similar to the measured one, and correlation between them was higher than 0.9 in all the datasets. On the other hand, the root mean square error increased after 15 days. This error was probably due to the change in physiological condition, the operating point of the pump, or mild intima formation