Ventricular Assist Device Sputnik: Description, Technical Features and Characteristics
In this paper, the first ventricular assist device (VAD) developed in Russia is described. This device is used to replace thefunction of left ventricle for patients with an acute heart failure. Basis of this VAD is the axial-flow pump, that assistsa left ventricle pump blood to the aorta. Prior to the system development, diverse international design practices werescrutinized. Researches has shown that axial-flow blood pumps can be successfully used as a bridge to transplantation,a destination therapy or a bridge to recovery. The weight of implantable pump is about 200 g. The pump rotor speedcan be varied within the range 5000...10000 rpm. Blood flow provided by the pump is up to 10 l/min. Components ofthe VAD include the microprocessor-based controller, four lithium-ion batteries, the charging unit, the notebook withinstalled control program and AC power adapter.
About 8 million people in Russia suffer from a heart failure.About 30% of them have an acute heart failure (Classes III and IV of New York Heart Association functionalclassification of heart failure). In its turn, an acute heartfailure is the most widespread reason of hospitalizationand death from heart diseases. The only way to save thepatient life at the end-stage heart failure is an implantationof donor’s heart or a device, that can partially or fullyreplace heart function. Other solutions, such as usage ofmedications or therapeutic treatment, does not providesufficient results . In USA about 2000 hearts beingtransplanted each year. In Russia this sum is significantlysmaller and is only reaches 100 transplantations.However, both these numbers stay almost unchangedyearly and remain much less than existing need fortransplants .
Determining the solution to the donor’s heart availabilityproblem does not seem possible in the near future.Therefore, implantation of the device, that can partiallyor fully replace heart function, is the only way to treat aheart failure.
Ventricular assist devices (VADs) are partially replace heart function. Nowadays, most widespread type of VADsis an axial-flow or a centrifugal pump with nonpulsatileflow [3, 4, 5]. In 2009 in USA usage of such systemsexceeded amount of donor heart transplantations .Necessity for the solution of the acute heart failureproblem and also usage of international experience withVAD formed the basis for the design of the Sputnik VAD.
Execution of the Sputnik VAD project started in 2009.The project is joint effort of:
- National Research University of ElectronicTechnology (MIET)
- OJSC Zelenograd Innovation-Technology Centerof Medical Equipment (JSC ZITCMT)
- FSBI “Academician V.I. Shumakov FederalResearch Center of Transplantology and ArtificialOrgans”, Ministry of Health of the Russian Federation.
- DONA-M LLC.
- BIOSOFT-M LLC.
Materials and Methods
The Sputnik VAD design is based on an axial-flow blood pump with nonpulsatile flow. It can provide flow up to 10l/min. An axial-flow pump was chosen due to clinicallyproven success of a nonpulsatile VAD usage: survivabilityof the patients with such systems exceed 70% two yearsafter the device implantation . Wearable parts of theSputnik VAD are illustrated in Fig. 1.
|Figure 1: Wearable parts of the Sputnik VAD|
The rotary type blood pump designed to produce bloodflow to support a weak left ventricle of patient’s heart.The pump includes a moving part, namely, impeller (rotorwith four blades) and a stationary part, namely, flowstraightener with three blades and diffuser. An externalpower supply is used to drive the pump. Two wearablebatteries are connected to the driving unit, which, in itsturn, connected to the pump by the percutaneous cablepassing through the skin.
The blood flow through the VAD is driven by the pumpimpeller rotor that contain a permanent NdFeB magnet, which is actuated by a brushless DC motor. Stator of themotor located inside the thin-walled titanium housing withdiameter of 16 mm. The weight of implantable pump isabout 200 g. The flow straightener consist of threestationary blades 1200 radially apart, straightening theincoming blood flow along the axial direction. The samecharacteristics of the straighteners have the ThoratecHeartMate II VAD (HMII; ThoratecCorp., Pleasanton, CA)and MicroMed HeartAssist 5 VAD (HA5; MicroMedCardiovascular, Inc., Houston, TX) . Three blades ofthe flow straightener direct flow into rotating impellerblades, minimizing eddy flow prior to entering into theimpeller. Magnetic impeller has four blades (3 and 6impeller blades for HMII and HA5, respectively ). Thespinning direction of the impeller is clockwise(counterclockwise and clockwise directions for HMII andHA5, respectively ). After impeller, blood flow movesinto the flow diffuser, which incorporates three twistedblades, located in the rotor output (HMII and HA5 have 3and 6 diffuser blades, respectively ). The inlet and outletsupport inflow and outflow needle bearings. Describeddesign of an implantable pump allows to minimize athrombosis and a hemocyte damage. The length of theimplantable pump is 81 mm (the length of HMII and HA5 81 mm and 71 mm, respectively ) and the maximumdiameter 34 mm (the maximum diameter of HMII and HA530 mm and 43 mm, respectively )
The blood pump profile is illustrated on Fig. 2. Thetunneling trocar is used to lead the percutaneous cable ofthe implantable pump outward from the patient’s tissue.Design of the implantable pump connection to acardiovascular system includes inflow and outflowcannulas, felt ferrule and a vascular prosthesis, sewed toascending aorta.
The external components include microprocessor-basedcontroller, lithium-ion batteries, the charging unit, thenotebook with installed control program and AC poweradapter.
The implantable pump is connected to themicroprocessor-based controller (size: 130.6 cm × 10.6 cm× 3.7 cm, weight: 280 g) by the percutaneous lead with asilicone or polyvinylchloride jacket (diameter: < 5 cm,length: <170 cm). The microprocessor-based controlleroperates the pump, regulates the pump speed, managespower sources, store pump parameters data. The SputnikVAD microprocessor-based controller design extensivelydescribed in . The controller provides an audible alarmif one of the power supply is lost.
The system power supplying is carried out by two lithiumionbatteries (size: 161 cm × 110 cm × 34 cm, weight: 570 g)or by an AC network. The Sputnik VAD package containset of four batteries. One pair of this batteries can provideup to 8 hours of the system support. The low-batteryalarm on the microprocessor-based controller alerts theuser when battery must be replaced and charged. Thecharging unit is used to charge the batteries (Fig. 3). Thisunit can monitor and charge up to four batteries at once.LED-indicators are used to display charge level of thebatteries. Two dual-colored diodes used to show thebattery charge level for the each channel. Maximumcharging time of the Sputnik VAD lithium-ion battery isless than 5 hours. Forced air cooling via two integral fans is used to cool the charging unit.
|Figure 2: Blood pump profile||Figure 3: Charging unit with four batteries (front panel view)|
The notebook with installed control program allows a user(e.g. doctor or technical expert) to:
- regulate prescribed value of the rotor speed installed inthe VAD driving unit;
- monitor system parameters during intensive andrecuperative stages of the patient’s treatment;
- periodically monitor system parameters during clinicaland ambulatory studies of the patient.
Results and Discussion
Results of the hydrodynamic pump evaluation (headpressure - pump flow and power uptake - pump flow) shownin Fig. 4 and 5. The pressure-flow characteristics werereceived during experiment with a basic hydraulic mock,like in . The mock incorporate a flowmeter (ME-11PXLClamp-on Tubing Flowsensors; Transonic Systems Inc.,Ithaca, NY, USA), inlet and outlet pressure transducers(MPX5050GP; Freescale Semiconductor, Austin, Texas,United States ), a resistance valve, reservoir and series offlexible polyvinyl chloride laboratory tubes (TYGON E-3603; Compagnie de Saint-Gobain, Courbevoie, Ile-deFrance,France), with an inner diameter of 12.7 mm.
|Figure 4: Flow-pressure (H-Q) curve of the Sputnik VAD||Figure 5: Flow- power uptake (P-Q) curve of the SputnikVAD|
Over the 2009 to 2012 period, the experimental animal studywas conducted . During this study the prototype ofthe implantable pump VAD Sputnik was tested. The VADwas connected by a scheme “left ventricle – aorta” fortwo different configurations: paracorporeal and implantedin a thoracic cavity. In 4 out of 6 experiments longevityequaled 74.5 ± 29 days. One experiment was ended due toan intraoperative heart fibrillation. Last experiment lasted8 days, but it was scheduled. Based on the results of theexperiments there were none pump thrombosis andmechanical wear of bearings. Anatomical and histologicalexamination of kidneys, liver and lungs did not spotoccurence of an ischemic zone and thrombembolia.
On June 9, 2012, first implantation of the Sputnik VADwas successfully conducted . The recipient was a 67years old man. After one month in a clinic the patient wasreleased, then he led normal life at home. Finally, on March5, 2013, the Sputnik VAD was successfully replaced by adonor heart.
Over the 2009 to 2014 period, development studies, invivo and in vitro studies, full range of certification testsand clinical testing of the Sputnik VAD were conducted inRussia . Results, gained during studies, and successfulpractices of system clinical usage is a good basis foradditional studies in the VAD field.
Currently, in MIET researches of a flow sensor integrationinto a VAD being conducted to provide an adaptive controlof the system operation based on the physiological humanneeds. Mathematical simulation of a cardiovascular system, considering a VAD implantation, is performed toexamine the pump control task . Also, studies wereconducted with the objective of ensuring wirelesstranscutaneous energy transfer for VAD .
This study was supported by the Russian ScienceFoundation grant ¹ 143900044.
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