Yong Soon Won

Hemodialysis using a valveless pulsatile blood pump.

Research on pulsatile blood pumps for extracorporeal life support has been widely performed because of the proven advantageous effects of blood pulsation. However, studies on the use of pulsatile blood pumps for hemodialysis are limited, although available evidence demonstrates that pulsatile blood flow has a positive influence on dialysis outcome. Therefore, the authors designed a new pulsatile pump, which is characterized by minimal-occlusion of blood-containing tubing, no requirement for valves, and no blood flow regurgitation. In-vitro hemolysis tests were conducted using fresh bovine blood, and the normalized index of hemolysis was adopted to compare blood traumas induced by the devised pulsatile pump and a conventional roller pump. In addition, experimental hemodialyses with a canine renal failure model were performed using the devised pump. Normalized index of hemolysis levels obtained was much smaller for the devised pulse pump (45 ± 21 mg/100 L) than for the roller pump (103 ± 10 mg/100 L), and no technical problems were encountered during dialysis sessions. Blood and dialysate flow rates were maintained at predetermined values and molecular removal was satisfactory. Postdialysis urea and creatinine reduction ratios were 61.8% ± 10.6% and 57.4% ± 9.0%, respectively. Pulsatile flow has usually been generated using pulsatile devices containing valves, but the valves cause concern in terms of the clinical applications of these devices. However, the described pulsatile pump does not require valves, and yet no blood flow regurgitation was observed.

Pulse Push/Pull Hemodialysis in a Canine Renal Failure Model

A new dialysis modality was devised to increase convective mass transfer. Blood and dialysate are circulated by a pulsatile pump, but with pulsatile flow patterns that are 180° out of phase, which causes blood-to-dialysate pressure gradients to oscillate between positive and negative. In the present study, hemodialytic performance of the devised modality was investigated using a canine renal failure model. Membrane hydraulic permeabilities (Kuf) and fiber bundle volumes (FBV) were measured after each dialysis session. Postdialysis Kuf and FBV were then compared with those with conventional high-flux hemodialysis. No complications concerning animals or technical problems with the devised modality were encountered. Urea and creatinine reductions were satisfactory. Postdialysis Kuf and FBV values were significantly reduced after hemodialysis sessions, but were higher for the new modality. The devised modality incorporated with blood and dialysate pulsation offers a simple but safe means new mode of hemodialysis.

Comparison of Hemolytic Properties of Different Shapes of Occlusion of Blood Sac in Occlusive‐type Pulsatile Blood Pump

The occlusive-type pulsatile extracorporeal blood pump (T-PLS, Seoul National University, Seoul, Korea) received the Communauté Européenne mark of the European Directives (2003) and Korea Food and Drug Administration approval (2004) for short-term application as an extracorporeal life support system. The pump system was recently upgraded in the ameliorated actuator head for reducing hemolysis, rather than in the existing actuator head. In this study, the hemolytic performance of the new pump system (assessed as the degree of occlusiveness of the blood sac) was compared with the existing one. A roller pump, the Stockert S3 (Stockert Instrumente GmbH, Munchen, Germany), was selected as a control device. Five tests were conducted for each pump, with each of these tests lasting for 6 h. A pump flow of 3 L/min with 50 beats per minute was included in the hemolytic test conditions. The lowest hemolytic results were obtained by the new pump system yielding a normalized index of hemolysis of less than 0.005 g/100 L, and this result was one-fourth that of the roller pump, Stockert S3.

A Dual-Chambered Hemodialyzer for Convection-Enhanced Hemodialysis

Convective clearance during hemodialysis (HD) improves dialysis outcomes in kidney failure patients, and, thus, trials have been undertaken to increase convective mass transfer, which is directly related to internal filtration rates. The authors designed a new hemodialyzer to increase the internal filtration rates, and here describe the hemodialytic efficacy of the devised unit. The developed dual-chambered hemodialyzer (DCH) contains two separate chambers for dialysate flow within a single housing. By placing a flow restrictor on the dialysate stream between these two chambers, dialysate pressures are regulated independently. Dialysate is maintained at a higher pressure than blood pressure in one chamber, and at a lower pressure in the other chamber. The dialysis performance of the DCH was investigated using an acute canine renal failure model. Urea and creatinine reductions and albumin loss were monitored, and forward and backward filtration rates were measured. No procedurally related malfunction was encountered, and animals remained stable without any complications. Urea and creatinine reductions after 4-h dialysis treatments were 75.2 ± 6.5% and 67.7 ± 8.9%, respectively. Post-treatment total protein and albumin levels remained at pretreatment values. Total filtration volume was 4.98 ± 0.5 L over 4 h, whereas the corresponding backfiltration (BF) volume was 4.77 ± 0.6 L. The developed dual-chamber dialyzer has the benefit of providing independent control of forward filtration and BF rates. HD using this dialyzer provides a straightforward means of increasing the internal filtration and convective dose.

In vivo experiment leading to clinical application of an electrohydraulic ventricular assist device with magnetic coupling.

We developed an electrohydraulic ventricular assist device with magnetic coupling. The integrated system consists of a blood pump, a water conduit for pressure transmission, a bellows type pumping sac, an actuator for transforming the circular motion of a motor to the linear motion of a pusher plate attached to the pumping sac with magnetic coupling, and a controller. The purpose of the coupling was to prevent excessive sucking against the atrial wall. Number 21 Medtronic Hall (Irvine, CA) mechanical valves were used in the inflow and outflow ports of the blood pump. Maximum dynamic stroke volume was 48 ml, and against a mean afterload of 100 mm Hg, maximum pump output was 7 L/min. Chronic in vivo experiments were performed in three sheep, and during these evaluations the system showed no noticeable problems related to mechanical or electronic devices. When left atrial pressure decreased below 0 mm Hg, the magnetic coupling system decoupled the pumping sac and pusher plate with satisfactory reliability. The device was clinically applied in a postoperative patient with chronic dilating cardiomyopathy, and no significant device related problems ensued. These results prove that the electrohydraulic ventricular assist system with magnetic coupling is a suitable ventricular assist device.

Further Development of the Moving-Actuator Type Total Artificial Heart

The electromechanical total artificial heart (TAH) developed at Seoul National University Hospital was verified as acceptable for human implantation through several successful animal experiments. In the last two years (1994–1996), the TAH was redesigned to be small (600–650 ml, total volume) and lightweight (approimately 950 g), and also improved to overcome three practical problems encountered in the animal experiments. First, we implemented modifications to the blood-pump housing to resolve the anatomical problem made apparent through the construction of a three-dimensional model of the TAH, the human thoracic cavity, and the large vessels, from magnetic resonance images and Angiogram-Computer tomography. Second, the intraventricular surface of the blood sacs was modified with fibrinolytic and anti-infective surface treatments. Third, the mechanism of regulation of cardiac output (CO) was improved by analyzing the measured pressure in the interventricular volume space (IVP). It proved beneficial to achieve the regulation of CO in response to the physiological demand, and to prevent atrial collapse due to the suction. The IVP, which accurately reflected the hemodynamic parameters, was used to predict the preload condition. These three improvements will assist in the application of the newly developed implantable electromechanical artificial heart for long-term implantation.

An Adaptive Cardiac Output Control for the Total Artificial Heart Using a Self-Tuning Proportional-Integral-Derivative (PID) Controller

The development of a control method for the totally implantable artificial heart (TAH) to regulate cardiac output according to the change in physiological demand was the goal of this study. The conventional proportional-integral-derivative (PID) controller was used for the automatic regulation of the cardiac output. Furthermore, using a fuzzy gain-tuning algorithm, the PID controller parameters were adaptively tuned to the optimal operating point of the process, which varied with hemodynamic disturbances. To determine the physiological demand, the interventricular pressure (IVP) inside the TAH was used to estimate inflow conditions. The negative peak value of the IVP at each diastolic period has a linear relation to the corresponding atrial pressure. Based on the relationship of atrial pressure to the IVP, the automatic control algorithm proposed regulates the optimal pump rate in terms of sufficient cardiac output delivery under a given venous return. To maintain a well-balanced left and right pump output from the volumetrically coupled, circular moving actuator type TAH, the automatic control also adjusts an asymmetric amount of the moving actuator stroke angle, which provides a different net output of the ventricles. The in vitro performance of the newly developed automatic control method was assessed using a mock circulatory system. Over a physiological range of preload, -3–15 mmHg of right atrial pressure (RAP) and 80–120 mmHg of aortic pressure (AoP), the cardiac output varied from 4.2 to 6.31/min with the left atrial pressure (LAP) maintained below 15 mmHg.