The current status of mechanical circulatory support

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.

The pulsatile impeller pump for left ventricular assist

Because of severe hemolysis, especially on producing pulsatile flow by changing the rotating speed of the impellers, the traditional centrifugal pump was rarely used for long-term support of the failing heart. We therefore developed a motor driven pulsatile implantable impeller pump. The pulsatility was achieved by changing the rotating speed via introducing a square waveform voltage into the motor coil. The impeller vane was designed to have both radial and axial curves according to the stream surface and stream lines to reduce the thrombosis and hemolysis. Nine calves weighing 80 to 100 kg were used. With the calves under endotracheal general anesthesia, left posterolateral thoracotomy was performed to connect the inflow tube with the left 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. Within 7 days, continuous monitoring of electrocardiogram, systemic and pulmonary arterial pressures, and central venous pressure were performed to adjust the pump flow to 40% to 50% of the cardiac output. During the survival of 4 to 54 days (mean 16.3 +/- 19.3 days with two calves surviving longer than 1 month), no significant deterioration of liver or renal function was noted. Because of bleeding, hemoglobin reduced from 11.4 +/- 1.8 to 9.0 +/- 1.3 g/dl, and the hematocrit decreased from 34.5 +/- 4.7 to 26.7 +/- 4.6%. No significant changes of free hemoglobin were noted. In our results, the device revealed competent pulsatile function without severe blood damage or organ dysfunction.

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.

Haemolysis test of non-pulsatile and pulsatile impeller blood pumps

Non-pulsatile and pulsatile impeller blood pumps have been developed. The non-pulsatile pump was compared with the Shanghai and Sarns 7000 roller pumps for haemolysis. Similarly, the pulsatile pump was compared with a pneumatic diaphragm pump and the Polystan pulsatile pump. In each test, one impeller pump and the pump it was being compared with were connected to two identical circulatory systems with the same volume of fresh citrated porcine blood, delivered at the same pressure and flow for several hours. Every half hour the free haemoglobin was measured and the index of haemolysis (IH) calculated. The mean IH of the non-pulsatile impeller pump was about 18% of the Shanghai roller pump and 29% of the Sarns 7000 roller pump; the IH of the pulsatile impeller pump was 16% of the diaphragm pump and 8% of the Polystan pulsatile pump.