Effect of counter-pulsation control of a pulsatile left ventricular assist device on working load variations of the native heart.

BACKGROUND: When using a pulsatile left ventricular assist device (LVAD), it is important to reduce the cardiac load variations of the native heart because severe cardiac load variations can induce ventricular arrhythmia. In this study, we investigated the effect of counter-pulsation control of the LVAD on the reduction of cardiac load variation. METHODS: A ventricular electrocardiogram-based counter-pulsation control algorithm for a LVAD was implemented, and the effects of counter-pulsation control of the LVAD on the reduction of the working load variations of the left ventricle were determined in three animal experiments. RESULTS: Deviations of the working load of the left ventricle were reduced by 51.3%, 67.9%, and 71.5% in each case, and the beat-to-beat variation rates in the working load were reduced by 84.8%, 82.7%, and 88.2% in each ease after counter-pulsation control. There were 3 to 12 premature ventricle contractions (PVCs) before counter-pulsation control, but no PVCs were observed during counter-pulsation control. CONCLUSIONS: Counter-pulsation control of the pulsatile LVAD can reduce severe cardiac load variations, but the average working load is not markedly affected by application of counter-pulsation control because it is also influenced by temporary cardiac outflow variations. We believe that counter-pulsation control of the LVAD can improve the long-term safety of heart failure patients equipped with LVADs.

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.

Computational analysis of the effect of the type of LVAD flow on coronary perfusion and ventricular afterload.

We developed a computational model to investigate the hemodynamic effects of a pulsatile left ventricular assist device (LVAD) on the cardiovascular system. The model consisted of 16 compartments for the cardiovascular system, including coronary circulation and LVAD, and autonomic nervous system control. A failed heart was modeled by decreasing the end-systolic elastance of the ventricle and blocking the mechanism controlling heart contractility. We assessed the physiological effect of the LVAD on the cardiovascular system for three types of LVAD flow: co-pulsation, counter-pulsation, and continuous flow modes. The results indicated that the pulsatile LVAD with counter-pulsation mode gave the most physiological coronary blood perfusion. In addition, the counter-pulsation mode resulted in a lower peak pressure of the left ventricle than the other modes, aiding cardiac recovery by reducing the ventricular afterload. In conclusion, these results indicate that, from the perspective of cardiovascular physiology, a pulsatile LVAD with counter-pulsation operation is a plausible alternative to the existing LVAD with continuous flow mode.

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 degrees 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 (K(uf)) and fiber bundle volumes (FBV) were measured after each dialysis session. Postdialysis K(uf) 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 K(uf) 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.

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.

Comparison of myocardial loading between asynchronous pulsatile and nonpulsatile percutaneous extracorporeal life support.

We hypothesized that myocardial loading can be increased when extracorporeal pulse flow occurs during systole, and that this may adversely affect myocardial working conditions in heart failure patients supported by extracorporeal life support (ECLS). This study was designed to compare myocardial loading and myocardial oxygen consumption/supply balance between nonpulsatile ECLS and asynchronized pulsatile ECLS in a myocardial stunning model. Thirteen, 23-42 kg dogs were allotted to a nonpulsatile group and an asynchronous pulsatile group. Coronary sinus lactate level, mixed venous oxygen consumption (MvO2), and left anterior descending coronary artery flow were measured. The real-time pressure of the left ventricle and the ascending aorta was monitored, and the lowest left ventricular pressure and tension time index were calculated. Our results showed that the lactate level and the lowest left ventricular pressure were lower in the pulsatile group than in the nonpulsatile group at 30 minutes after ECLS was applicated (p < 0.05, respectively). Tension time index in the pulsatile ECLS group was substantially lower than in the nonpulsatile group. Left anterior descending coronary flow did not show significant difference between the two groups. In conclusion, asynchronous pulsatile ECLS may also be superior to nonpulsatile ECLS in myocardial volume unloading and oxygen consumption/supply balance.

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.

Durability improvement of polymer chamber of pulsatile extracorporeal life support system in terms of mechanical change.

Twin Pulse Life Support, T-PLS has received the CE mark (2003) and Korea Food and Drug Administration (KFDA) approval (2004) for short-term application as an Extracorporeal Life Support system (ECLS). T-PLS's original intention was to apply for not only short-term but also long-term application such as Extracorporeal ventricular assist device (VAD). Hence, a long-term durability test was conducted. The 1-year reliability of the systems tested in this study did not meet the STS/ASAIO standard of 80% reliability with 60% confidence for a 1-year mission life. However, without the disposable units, which are only designed to operate for 6 h, the 1-year reliability exceeded the STS/ASAIO standard of 80% reliability with 60% confidence. In this study, by using the existing analysis methods and analyzing the root cause of the failure used by a numerical analysis. As eliminating or mitigating of the root cause of the failure, we improved the durability of blood chamber and evaluated the performance of the modified system via the hemolysis test.

Convection-enhanced high-flux hemodialysis.

Internal filtration contributes to convective clearance in high-flux hemodialysis but its contribution is limited by low pressure gradients. Therefore, a modification using a conventional dialyzer was conceived to enhance internal filtration and backfiltration (BF) rates. The modified dialyzer includes two longitudinal independent regions for blood flow, which were created by redesigning dialyzer caps. Blood pressures remained higher than dialysate pressures in one region and lower in the other region, allowing continuous internal filtration and BF in these respective regions. Modified and conventional dialyzers were compared in terms of pressure gradients and solute clearances. Thus, our experiments involved two groups: the modified dialyzer group and the conventional dialyzer group. A renal failure model was established using a dog weighing 25-30 kg by renal artery and vein ligation. With the exception of the dialyzers, experimental conditions were identical in the two groups. The pressure gradients between blood and dialysate were much higher for the modified dialyzer than for the conventional dialyzer. No significant differences were observed with respect to small solute clearances between the two groups, but mid-range solute clearances were significantly higher in the modified group. More optimization is required before the devised unit can be used clinically. However, the devised unit offers a straightforward means of regulating internal filtration and BF rates.

In vivo evaluation of the pulsatile ECLS system.

Extracorporeal life support (ECLS) systems have been increasingly applied to groups of patients with cardiorespiratory failure, including pediatric and adult patients with respiratory failure. Current pulsatile ECLS systems use a single pulsatile blood pump that generates a high inlet pressure in the membrane oxygenator. To minimize this high inlet pressure, we have developed a new and improved ECLS system, twin pulse life support (T-PLS). To analyze the advantages of T-PLS, we have compared T-PLS with a single pulsatile ECLS system. An acute heart failure model was constructed by using a pulmonary artery banding technique. Fourteen pigs (22-31 kg) were used, with cardiac outputs of 2.0 l/min and a V/Q ratio set at 1. Cannulae of 28 Fr and 18 Fr were used in the right atrium and aorta, respectively. A polypropylene hollow-fiber membrane oxygenator and four polymer valves 30 mm in diameter were used in the T-PLS system. In the single pulsatile ECLS system, Medtronic Hall monostrut valves were used. To evaluate blood cell trauma in both pulsatile ECLS systems, plasma free hemoglobin (fHb) was measured while the systems were in use. The results show that fHb levels in T-PLS are lower than fHb levels in the single pulsatile ECLS system. There is a possibility that T-PLS could be used as an ECLS system for emergency situations.

Aortic valve involvement in Behçet's disease. A clinical study of 9 patients.

OBJECTIVES: To assess the clinical features, pathologic findings, postoperative results and the effects of immunosuppressive therapy in patients with Behçet's disease (BD). METHODS: We reviewed the postoperative course of the 9 BD patients who underwent a total of 17 aortic valve replacement procedures with prosthetic valves. RESULTS: Histological examination of the aortic valve commonly revealed diffuse myxoid degeneration (75 percent). Of 17 valve replacement surgeries, 13 surgeries resulted in complications, such as detachment of the prosthetic valve with perivalvular leakage and dehiscence of the sternotomy wound, within an average of 5 months (range from 1 month to 14 months). The rate of prosthetic valve detachment was 76 percent (13 of 17 surgeries). Four of the 9 patients (44 percent) who underwent aortic valve replacement procedures died of heart failure or infection associated with the detachment of the prosthetic valve, and perivalvular leakage within an average of 9 months. Aortic insufficiency associated with dehiscence of the prosthetic valve developed in 11 of 12 surgical cases (92 percent) with a mechanical valve and 2 of 5 surgical cases (40 percent) with tissue valves. Thirteen of 15 surgeries (87 percent) which were not given postoperative immunosuppressive therapy developed complications, while none of 2 surgeries that used postoperative immunosuppressive therapy with prednisolone (1 mg/kg/day) and azathioprine (100 mg/day) had these complications. CONCLUSION: The rates of prosthetic valve detachment in BD involving aortic valve were higher than those of other diseases. Aortic valve involvement was also one of the poor prognostic factors in BD. Intensive postoperative immunosuppressive therapy and surgical methods may be important factors for postoperative results.