Pulsatile Impeller Research Articles

R&D of a Pulsatile Rotary Heart Pump Imitating the Native Ventricle

It is evident that a pulsatile flow is important for blood circulation because the flow pulsatility can reduce the resistance of peripheral vessels. It is difficult, however, to produce a pulsatile flow with an impeller pump, since blood damage will occur when a pulsatile flow is produced. Further investigation has revealed that the main factor for blood damage is turbulence shear, which tears the membranes of red blood cells, resulting in free release of haemoglobin into the plasma, and consequently lead to haemolysis. Therefore, the question for producing a pulsatile flow with low haemolysis becomes how to develop a pulsatile impeller pump with less turbulence? The authors have successively developed a pulsatile axial pump and a pulsatile centrifugal pump. In the pulsatile axial pump, the impeller reciprocates axially and rotates simultaneously. The reciprocation is driven by a pneumatic device and the rotation by a DC motor. For a pressure of 40mm Hg pulsatility, about 50mm axially reciprocation amplitude of the impeller is desirable. In order to reduce the axial amplitude, the pump inlet and the impeller both have cone-shaped heads, thus the gap between the impeller and the inlet pipe changes by only 2mm, that is, the impeller reciprocates up to 2mm, a pressure pulsatility of 40mmHg can be produced. As the impeller rotates with a constant speed, low turbulence in the pump can be expected. In the centrifugal pulsatile pump, the impeller changes its rotating speed periodically; the turbulence is reduced by designing an impeller with twisted vanes which enable the blood flow to change its direction rather than its magnitude during the periodic change of the rotating speed. In this way, a pulsatile flow is produced and the turbulence is minimized. Compared to the axial pulsatile pump, the centrifugal pulsatile pump needs only one driver and thus has more application possibilities. The centrifugal pulsatile pump has been used in animal experiments. The pump assisted the circulation of calves for several months without harm to the blood elements and the organ functions of the experimental animal. The experiments demonstrated that the pulsatile impeller is the most efficient pump for assisting heart recovery, because it can produce a pulsatile flow like a diaphragm pump and has no back flow as what occurs in a non-pulsatile rotary pump; the former reduces the circulatory resistance and the later increases the diastole pressure in aorta, and thus increase the perfusion of coronary arteries of the natural heart.

Computational modelling and evaluation of cardiovascular response under pulsatile impeller pump support

This study presents a numerical simulation of cardiovascular response in the heart failure condition under the support of a Berlin Heart INCOR impeller pump-type ventricular assist device (VAD). The model is implemented using the CellML modelling language. To investigate the potential of using the Berlin Heart INCOR impeller pump to produce physiologically meaningful arterial pulse pressure within the various physiological constraints, a series of VAD-assisted cardiovascular cases are studied, in which the pulsation ratio and the phase shift of the VAD motion profile are systematically changed to observe the cardiovascular responses in each of the studied cases. An optimization process is proposed, including the introduction of a cost function to balance the importance of the characteristic cardiovascular variables. Based on this cost function it is found that a pulsation ratio of 0.35 combined with a phase shift of 200° produces the optimal cardiovascular response, giving rise to a maximal arterial pulse pressure of 12.6 mm Hg without inducing regurgitant pump flow while keeping other characteristic cardiovascular variables within appropriate physiological ranges.

Numerical Modeling of Hemodynamics with Pulsatile Impeller Pump Support

There is significant interest in the development and application of variable speed impeller-pump type ventricular assist devices designed to generate pulsatile blood flow. However, no study has so far been carried out to investigate the systemic cardiovascular response to various aspects of pump motion. In this article, a numerical model is constructed for the simulation of the cardiovascular response in the heart failure condition under representative cases of pulsatile impeller pump support. The native cardiovascular model is based on a previously validated model, and the impeller pump is modeled by directly fitting the pressure-flow curves that describe the pump characteristics. The model developed is applied to study circulatory dynamics under different degrees of phase shift and pulsation ratio in the pump motion profile. The characteristic variables are discussed as criteria for the evaluation of system response for comparison of the pulsatile flows. Simulation results show that a constant pump speed is the most efficient work mode for the rotary pump, and with the application of either a phase shift of 75% and a pulsation ratio of 0.5, or a phase shift of 42% and a pulsation ratio of 0.55, it is possible to generate arterial pulse pressure with the maximal magnitude of about 28 mmHg. However, this is achieved at the cost of reduced cardiac output and pump efficiency.

Artificial Heart Rejects High Tech? Lessens Learnt from Non-pulsatile VAD with Straight Impeller Vanes

Despite the progresses in developing pulsatile impeller pump and impeller total heart, as well as in applying streamlined impeller vanes, the best results in application of artificial heart pumps have been achieved by nonpulsatile univentricular assist pump with straight impeller vanes until now. It seems all efforts and successes have been done in vain because artificial heart rejects Hi-Tech! This paper recalls some important achievements in R&D of artificial heart in past 25 years and shares author’s experiences with the readers.

Recent progress in developing durable and permanent impeller pump.

Since 1980s, the author's impeller pump has successively achieved the device implantability, blood compatibility and flow pulsatility. In order to realize a performance durability, the author has concentrated in past years on solving the bearing problems of the impeller pump. Recent progress has been obtained in developing durable and permanent impeller blood pumps. At first, a durable impeller pump with rolling bearing and purge system has been developed, in which the wear-less rollers made of super-high-molecular weight polythene make the pump to work for years without mechanical wear; and the purge system enables the bearing to work in saline and heparin, and no thrombus therefore could be formed. Secondly, a durable centrifugal pump with rolling bearing and axially reciprocating impeller has been developed, the axial reciprocation of rotating impeller makes the fresh blood in and out of the bearing and to wash the rollers once a circle; in such way, no thrombus could be formed and no fluid infusion is necessary, which may bring inconvenience and discomfort to the receptors. Finally, a permanent maglev impeller pump has been developed, its rotor is suspended and floating in the blood under the action of permanent magnetic force and nonmagnetic forces, without need for position measurement and feed-back control. In conclusion, an implantable, pulsatile, and blood compatible impeller pump with durability may have more extensive applications than ever before and could replace the donor heart for transplantation in the future.

Development of a Totally Implantable Pulsatile Centrifugal Pump as a Ventricular Assist Device

The Taita No. 1 ventricular assist device (T-VAD) is a totally implantable pulsatile impeller centrifugal pump driven by a magnetically suspended motor. The flow can achieve 2.01 +/- 0.17 L/min against a pressure of 100 mm Hg under 0.266 +/- 0.017 amp and 13.55 +/- 0.41 voltage. The speed was around 3,500 rpm. It consumed less than 6 W of power, resulting in less heat production and mechanical bearing complications. The impeller vane was designed to have both radial and axial curves according to the stream surface and stream lines to reduce thrombosis and hemolysis. Eight calves weighing 80 to 100 kg (mean 87 +/- 12 kg) were used for experiments. With the calves under general anesthesia, left posterolateral thoracotomy was performed to connect the inflow tube with the atrial appendage and to anastomose the outflow tube with the descending aorta. The calves usually awoke and stood up within hours after discontinuation of anesthetics. The mean survival of the calves was 75 +/- 42 days (range 33-148 days). The terminations of experiments were mainly due to infection. During the course of pumping, no significant deterioration of liver or renal function was noted. The evaluation of serum samples from the implanted calves indicated that hemolysis was not associated with use of the T-VAD. The average daily free hemoglobin level was 8.08 +/- 3.05 mg/dl, which was less than the set limit of 20 mg/dl. The red blood cell and platelet count and hemoglobin of implanted animals were within the normal range. In our results, the T-VAD provided competent pulsatile function without severe blood damage or organ dysfunction.

How to produce a pulsatile flow with low haemolysis?

It is evident that a pulsatile flow is important for blood circulation because the flow pulsatility can reduce the resistance of peripheral vessels. It is difficult, however, to produce a pulsatile flow with an impeller pump, since blood damage will occur when a pulsatile flow is produced. Further investigation has revealed that the main factor for blood damage is turbulence shear, which tears the membranes of red blood cells, resulting in free release of haemoglobin into the plasma, and consequently leads to haemolysis. Therefore, the question for developing a pulsatile impeller blood pump is: how to produce a pulsatile flow with low haemolysis? The authors have successively developed a pulsatile axial pump and a pulsatile centrifugal pump. In the pulsatile axial pump, the impeller reciprocates axially and rotates simultaneously. The reciprocation is driven by a pneumatic device and the rotation by a dc motor. For a pressure of 40 mm Hg pulsatility, about 50 mm axial reciprocating amplitude of the impeller is desirable. In order to reduce the axial amplitude, the pump inlet and the impeller both have cone-shaped heads, and the gap between the impeller and the inlet pipe changes by only 2 mm, that is the impeller reciprocates up to 2 mm and a pressure pulsatility of 40 mm Hg can be produced. As the impeller rotates with a constant speed, low turbulence in the pump may be expected. In the centrifugal pulsatile pump, the impeller changes its rotating speed periodically; the turbulence is reduced by designing an impeller with twisted vanes which enable the blood flow to change its direction rather than its magnitude during the periodic change of the rotating speed. In this way, a pulsatile flow is produced and the turbulence is minimized. Compared to the axial pulsatile pump, the centrifugal pulsatile pump needs only one driver and thus has more application possibilities. The centrifugal pulsatile pump has been used in animal experiments. The pump assisted the circulation of calves for several months without harm to the blood elements and the organ functions of the experimental animal. The experiments demonstrated that the pulsatile impeller pump is the most efficient pump for assisting heart recovery, because it can produce a pulsatile flow like a diaphragm pump and has no back flow as occurs in a non-pulsatile rotary pump; the former reduces the circulatory resistance and the latter increases the diastole pressure in aorta and thus increases the perfusion of coronary arteries of the natural heart.

Pulsatile impeller heart: a viable alternative to a problematic diaphragm heart

The impeller blood pump with its simplicity has many advantages compared with the diaphragm pump, but the nonpulsatile property has limited its applications. To make the impeller pump pulsatile, many investigations have been made in vain because of resulting haemolysis. The author has succeeded in producing a pulsatile blood flow with a centrifugal pump, by means of the streamlined design of the impeller. The vane and shroud coincide with the blood stream surface in the pump, to eliminate the turbulence and stasis of the blood flow, which are the main factors in haemolysis and thrombosis. The pulsatility of the blood pressure and flow rate is achieved by changing the rotating speed of the impeller periodically, by introducing a square wave form voltage into the motor coil. The velocity variation of the blood cells due to the changing rotating speed of the impeller is minimized by using twisted impeller vanes, thus reducing the additional Reynolds shear, which causes the additional haemolysis in the pump. In vitro testing demonstrated that the haemolysis index of the pulsatile impeller pump is slightly higher than that of the author's nonpulsatile impeller pump but clearly less than that of other pulsatile blood pumps. The in vivo evaluations indicated that no blood damage occurred and that all haematological and biochemical data kept within a normal range during left ventricular assist experiments in calves for up to 11 days. A pulsatile impeller total heart has been developed. Two pumps are located on both sides of and driven by a d.c. motor. As the motor changes its rotating speed periodically, the left and right pumps eject the blood simultaneously, and the volume equilibrium of both pumps is achieved naturally. Acute biventricular assist experiments in pig confirmed that the device caused no blood damage.

In vivo testing of a pulsatile implantable impeller pump as a left ventricular assist device used in calves.

A pulsatile implantable impeller pump was tested as a left ventricular assist device in five calves. The experiments lasted for 4-11 days. Death or termination was mainly due to respiratory complications or bleeding, irrelevant to the pump itself. As indicators of haemolysis, thrombogenesis, renal and hepatic functions, free haemoglobin (FHb), haematocrit (Hct), platelet number (Plt), lactate dehydrogenase (LDH), blood urea nitrogen (BUN), creatinine, serum glutamic oxalacetic transaminase (GOT) and total bilirubin were measured preoperatively, at the beginning of the pumping (pump on), six hours later and every day thereafter. The data indicated that the pump caused no severe blood damage or organ dysfunction. Thus, the feasibility of a pulsatile centrifugal pump was demonstrated. The pump with its driver weighs 110 g and is capable of delivering a blood flow up to 8 l/min against 100 mmHg mean pressure.

In vivo studies of pulsatile implantable impeller assist and total hearts.

A pulsatile impeller assist heart and a total heart were tested as a chronic left ventricular assist device in 5 calves and an acute biventricular assist device in 4 pigs respectively, to evaluate their blood compatibility. During the left ventricular assist experiments, the indicators for hemolysis, thrombogenesis, renal dysfunction, and hepatic dysfunction were measured preoperatively, at the beginning of the pumping, 6 h postoperatively, and every following day. The results demonstrated that the impeller assist heart causes no severe blood damage nor organ dysfunction in the experiments lasting up to 11 days. In biventricular assist experiments, the number of red blood cells, white blood cells, platelets, and the hematocrit, hemoglobin, free hemoglobin, and lactate dehydrogenase levels were tested preoperatively at the beginning of the pumping and every 2 h postoperatively. The data remained in acceptable ranges during experiments lasting 6 h. It is confirmed that the authors' impeller assist heart and total heart have the advantages of simplicity, implantability, and pulsatility with good blood compatibility.

Pulsatile Blood Flow from Impeller Pump: A Dream Has Come True

For decades many investigations have been made on producing a pulsatile blood flow with an impeller pump. It has been foiled because of excessive hemolysis. Other investigators foretold that a pulsatile centrifugal pump is impossible in the near future, without increasing the complexity of the system remarkably. The author has presevered in this study and made progress steadily. An axial pulsatile impeller pump with constant-rotating speed was developed, in which the impeller reciprocates along its axis while rotates. Meanwhile, a pulsatile implantable impeller centrifugal pump is now in animal surviving experimental stage. The pulsatility of the blood flow is achieved by changing the rotating speed of the impeller periodically, via introducing a square wave form voltage into the motor coil. The hemodynamic and physiological superiorities to both nonpulsatile impeller pump and diaphragm pump were demonstrated. The hematological and biochemical data indicated low hemolysis and thrombogenesis, low renal and heptic dysfunction. Furthermore, a pulsatile implantable impeller total heart has completed its acute biventricular assist animal experiments. This is an almost unique total heart at the present, it is driven by a single motor, the left and right pumps eject the blood simultaneously, and the volume equilibrium of both pumps is achieved naturally. The dream of producing a pulsatile blood flow with an impeller pump has come true. Doubtlessly, an impeller heart with simplicity, pulsatility, implantability, compatibility and reliability, will be a viable alternative to diaphragm heart, really.

Haematological variations in pigs during experimental left ventricular assistance with a pulsatile impeller pump

Left ventricular assistance with a pulsatile impeller pump was performed on 5 pigs. The pump delivered the blood from the left atrium to the aorta. The by-pass flow was adjusted to 40% of the total flow. All of the haematological variations were measured every hour. The results demonstrated that the pulsatile impeller pump caused less erythrocyte but more platelet damage than the nonpulsatile impeller pump in same experiments by dogs. The free haemoglobin was unchanged but lactate dehydrogenase increased remarkably in 6h. Compared with the same experiments of the pulsatile impeller pump in goats and roller pump in pigs, it seems that the pig erythrocytes have more endurance to shear stress than that of dogs and goats, and pig platelets are more sensitive to mechanical force than those of other animals. The chronic experiment of pulsatile impeller pump is now in the planning stage for further investigations.

In Vivo Evaluation of a Pulsatile Impeller Total Heart

For the in vivo evaluation of a pulsatile impeller total heart, biventricular assistance was performed in five pigs weighing 30-50 kg. The left pump delivered blood from the left atrium to the aorta, and the right pump from the right atrium to the pulmonary artery. The bypass flow on both sides was adjusted to about 40-50% of the total flow. Hematologic variables were measured every 2 hr during the 6 hr experiments. Results demonstrated that the pulsatile impeller total artificial heart causes no blood damage and can be used in chronic survival experiments.

Low haemolysis pulsatile impeller pump: design concepts and experimental results

A pulsatile fully implantable impeller pump with low haemolysis has been produced by developing a pulsatile impeller for a nonpulsatile pump also developed in this laboratory. The impeller was designed according to the 3-dimensional theory of fluid dynamics. The impeller shroud retains the same parabolic form and the vane has a form compacted by a radial logarithmic spiral and an axial helical spiral so that the absolute vibration velocity of the blood in a peripheral direction is a minimum as the impellar changes its speed periodically to generate a physiological pulsatile blood flow. Thus the Reynolds shear and the Newton shear are a minimum for the required pulse pressure. The mean volume and mean pressure are controlled by adjusting the voltage. The shape of the pressure pulse is determined by a square was of vollage and the systole/diastole ratio. In order to abolish regurgitation of the pump, a 40 per cent systole period and a 5 V voltage pulse are desirable for 40 mmHg pulse pressure (80–120 mmHg mean pressure). The pulse frequency has almost no effect on pump output. The pump can delivery 4 l/min mean volume and 100 mmHg mean pressure (40 mmHg pulse pressure), and these conditions result in an index of heamolysis (IH) for porcine blood of 0.020—only slighly more than the nonpulsatile pump (0.016). When the pulsatile impeller was used under nonpulsatile conditions its IH was almost doubled, but when the nonpulsatile impeller was used under pulsatile conditions the IH reached 0.13. The power consumption is approximately equal to that for the nonpulsatile pump: 3 W for 4 l/min and 100 mmHg output. The pump weights 240 g (including 190 g for the motor) and, because a commercial motor has been used, costs only a few hundred US dollars.