Technical Support of Preclinical Hydrodynamic and Functional Tests of New Medical Mechatronic Peristaltic Blood Pumps Developed by Central Research Institute of Robotics and Cybernetics

Corresponding Author: Vyacheslav Valentinovich Kharlamov Russian State Scientific Center for Robotics and Technical Cybernetics, St. Petersburg, Russia Email: v.harlamov@rtc.ru Abstract: The article considers the results of scientific research works on creation of hydrodynamic and functional experimental benches for preclinical physiological tests of new mechatronic peristaltic blood pumps. The conclusion states the need in carrying out such tests before the start of biological experiments involving animals. An example of the device developed at Central Research Institute of Robotics and Cybernetics-a centrifugal pump-having optimal physiological characteristics is provided. The novelty of the proposed approaches to creation of hydrodynamic and functional experimental benches, as well as their technical equipment and data obtained as a result of the experiments, form a new approach to conduct of preclinical and physiological tests of mechatronic peristaltic pumps.


Introduction
Perfusion complex for extracorporeal circulation is intended for temporary full or partial replacement of the heart pump function (Kay, 2004;Reznik, 2010). It ensures optimal level of blood circulation and metabolic process in the patient's organism or in an isolated organ.
The key element of any perfusion unit is a pump, which supports continuous circulation of blood (chemotherapeutic agent solution) (Khaustov, 1998). Comparative preclinical hydrodynamic and functional tests of medical mechatronic peristaltic pumps Mars and НР-6 peristaltic pumps (in pulse mode) (Senchik, 2005) and a peristaltic pump developed by Central Research Institute of Robotics and Cybernetics (in constant mode) were carried out at Central Research Institute of Robotics and Cybernetics (Fig. 1).

Methods and Techniques
An experimental hydrodynamic bench ( Fig. 2 and 3) with circulation of model fluid in the closed loop was created for study of pump characteristics. The unit allows for connection of tubes having a diameter of 1 to 12 mm to the tested pump (8), measurement of pulsing flow rates and pressures in the loop, entry of data in a computer and their processing with calculation of necessary parameters. Saline is used as working fluid to ensure operation of the electromagnetic transducers; starch (0.5 g L −1 ) is added to the saline to ensure operation of the ultrasonic transducers. In order to model blood viscosity, 36% water-glycerin mixture was used.
A measuring cell (4) allowing performance of fluid flow measurement by the ultrasound method in tubes with a diameter of 1 to 12 mm was designed and manufactured for mounting of an ultrasonic transducer. Signals from the ADOP analogue Doppler flow meter (3) were sent to L-154 AD converter board of Pentium-200MMX system unit (1).  (Senchik, 2005) A silicone tube (7) was used in the roller pump (8) as a working segment. The difference between inlet and outlet pressure is measured with a pressure sensor (6). The pressure sensor is connected to the L-154 AD converter.
At the outlet, the tube passes through the measuring cell (4). Ultrasonic transducer with operation frequency of 4 MHz is connected to ADOP unit where the signal is processed by the analogue circuit and to Speсtra-300 Doppler blood flow analyzer (1) where the signal is processed digitally and displayed on the monitor in realtime. A clamp (5) that allows changing outlet/inlet pressure by pinching the tube is installed on the inlet/outlet of the pump. The pump sucks the working fluid from the tank (10). Figure 1(B) for the bench configuration used in calibration of the flow meters. In this mode, the fluid from the main outlet tube comes into the measuring cylinder (11) and then to the storage tank (10). Pulse operation of Mars pump was tested within the following parameter range: • d = 13 mm-inside diameter of the working segment tube • T1 = 0.5-4 sec-fluctuation time • T2 = 0.4-2 sec-pump operation time (systole) An experimental setup (Fig. 4), which presents a system consisting of a pump (1) + hydraulic loop (2), was created for conduct of the tests.
The setup provides measurement of flow rate and pressure pulses and also entry of data into the computer (7). Water was used as the working fluid. Saline was added to the solution to support operation of electromagnetic flow meters. A silicone tube with inner diameter of 13 mm was used as a working segment tube. Signals from FA-100S electromagnetic sensor (4) (diameter of 10 mm) were sent to Nihon Kohden MF-46 electromagnetic flow meter (5) connected to the L-154 AD converter built in the system unit of the computer. Outlet pressure is measured by the pressure sensor (3) connected to the L-154 AD converter. The pumped working fluid is held in a tank in case of opened loop A (in case of closed loop-B). There is a pump operation control system (6), which lets control time of operation and off state of the pump.

Results
As an example, we present the test results of Mars pump (Fig. 5) Perfusion of whole blood in the closed standard loop was performed for blood injury assessment experiments in the mentioned pumps. Quantity of free hemoglobin of blood plasma was determined upon completion of the perfusion time.
Statistically credible increase of free plasma hemoglobin content was noted both for HP-6 pump and Mars pump at the end of the surgery using p<0.001. In addition, the highest increase of this indicator was noted while using НР-6 pump. At the same time, free plasma hemoglobin at the end of a 4 h perfusion of whole blood in the closed standard loop using Mars pump was 0.154±0.012 g L −1 . This indicator does not exceed the values obtained in the experiment for roller pumps of foreign manufacturers (0.24 g L −1 ) (Chang et al., 2003;De Vries et al., 2003;Fieux et al., 2009;Garcia et al., 2000;Harper et al., 2006;Linfert et al., 2009) (Fig. 6). depending on time of circulation of whole blood in the closed loop using Mars (n = 10) and НР-6 (n = 10) peristaltic pumps (Reference-literature data (Chang et al., 2003;De Vries et al., 2003;Fieux et al., 2009;Garcia et al., 2000;Harper et al., 2006;Linfert et al., 2009)) Such satisfactory performance of blood injury could be achieved due to proper precise manufacture of the roller mechanism of Mars perfusion pump and use of an advanced stepper motor with improved dynamic characteristics in the drive (Chang et al., 2003;De Vries et al., 2003;Fieux et al., 2009;Garcia et al., 2000;Harper et al., 2006;Linfert et al., 2009).

Discussion
The article provides information about technical support of the preclinical hydrodynamic and functional tests of mechatronic peristaltic medical blood pumps. As a result of the accomplished tests, we could find that the blood injury performance was at an acceptable level when testing the perfusion and centrifugal pumps manufactured by Central Research Institute of Robotics and Cybernetics and still below that level when using similar devices of different designs.

Conclusion and Further Research
In order to carry out preclinical hydrodynamic and functional study of the new medical mechatronic peristaltic pumps, it is desirable to use experimental benches created at Central Research Institute of Robotics and Cybernetics. It is reasonable to use the hardware system based on the centrifugal pump for the purpose of ensuring the physiological parameters of perfusion to perform extracorporeal circulation and perfusion treatment.
Hydrodynamic tests should precede biological and experimental study in animals for the purpose of decreasing the volumes of the latter in conformity with the principles of the evidence-based medicine.