Study Of Hemodialysis Treatment Instrument's Control System

The basic function of hemodialysis instrument (manual renal) is to replace the human being's kidney. This instrument can clean out the metabolized waste of the body and reduce most of poisonous substances in blood;hemodialysis and ultrafiltration are the usual methods to complete these functions. When solute passes through half film from the denser solution to the thinner one,this process is called dialysis. Ultrafiltration is the movement of the liquid passing through the half film when the liquid is affected by the pressure grads,which can be described precisely as the molecule moves from the blood to the dialytic solution. With dialysis to clean out the metabolized waste,the nephritic patients can keep a balance of electrolyte,acid and alkali in body;with ultrafiltration the patients can clean out resorted molecule in body. These are the basic theories of hemodialysis.At present,most of hemodialysis instruments are imported from foreign countries and the prices are very high. On the other hand,the number of renal failure patients is increasing sharply. Therefore,the main purpose of this project is to make a research and design a new-style hemodialysis instrument so as to meet the massive demand of this equipment in our country.The paper systematically introduces the basic theory of hemodialysis firstly,and the using procedure of the equipment secondly. The functions of hemodialysis instrument include the blood circuit,the dialysate circuit,the pressure detection,the air bubble detection and temperature detection. The second part introduces the hardware design of the whole instrument in the first period,which is based on the ISA interface,hi this period the equipment precedes its operation and safe detection mainly by the ISA interface card. Also the patients' data,the setting of the blood flux and the display and backup of data are all executed on the computer. The emphasis of this article is the design in the second period,which is based on the PIC microchip interface,because at present embedded structure is adopted by most of medical instruments so that it can run separately without computer,hi this part the article specifically introduces the interface circuit of PIC16F877 single-chip,which includes the acquisition of A/D signals and the serial communication between the single-chip and computer,the design of Complex Programmable Logic Device (CPLD) and the using of Hardware Describe Language(VHDL) to control the rotate speed of 4-route stepping motors. Finally it describes the design of hemodialysis management software,and especially the methods to display the historical curves and real-time curves in the data acquisition.The author has already realized the design of hardware and software of the whole hemodialysis instrument. Furthermore,the equipment can work stably and safely. The tests of this system show that datum and results to measure are almost identical with the object of research.