微控制器控制低温系统

Journal of Medical Systems, Vol. 29, No. 5, October 2005 ( C© 2005) DOI: 10.1007/s10916-005-6101-9 A New Microcontroller Supervised Thermoelectric Renal Hypothermia System Hakan Is¸ik1 In the present study, a thermoelectric system controlled by a microcontroller is devel- oped to induce renal hypothermia. Temperature value was managed by 8-byte micro- controller, PIC16F877, and was programmed using microcontroller MPASM pack- age. In order to ensure hypothermia in the kidney 1–4 modules and sensors perceiving temperature of the area can be selected. Temperature values are arranged proportion- ately for the selected area and the determined temperature values can be monitored from an Liquid Crystal Display (LCD) screen. The temperature range of the system is between −50 and +50◦C. Renal hypothermia system was tried under in vivo condi- tions on the kidney of a dog. KEYWORDS: renal hypothermia; microcontroller; thermoelectric module. INTRODUCTION Recent studies about renal surgery are in search of a bloodless and long-lasting method that does not cause renal dysfunction. This can be achieved by working in a hypothermic setting. In a hypothermic setting, cells slow down their metabolism by consuming less energy and oxygen. Thus, the cells are protected and resume their functions after ischemia. The most important issues in long-lasting parenchymatous renal surgery are to provide an operation medium free of blood and to prevent renal dysfunction in the postoperative period. The method most easily used for this purpose is clamping the renal artery. The disadvantage of the concerned method is that it is limited to a period of 30min in order to avoid loss of function in the kidney. It was found that warm ischemia for over 30min leads to renal dysfunction.(1) Ward established that optimal renal hypothermia was at 15◦C.(1) Among the methods used for hypothermia until the present time, the one that is most frequently and easily used is in situ cooling of the renal surface by external ice-slush.(2) Another method is to provide hypothermia by a cooling instrument that is put around the 1Electronic Department, Technical Education Faculty, Selcuk University, Konya, Turkey. 441 0148-5598/05/1000-0441/0 C© 2005 Springer Science+Business Media, Inc. 442 Is¸ik kidney and that completely surrounds it.(3) Besides these two, there is an invasive method of renal artery perfusion.(4) Retrograde endoscopic renal hypothermia is another method used in this field.(5) In surface hypothermia performed using the well-known classical ice-slush, it is difficult to maintain the temperature at the same value in the renal cortex. Since the ice-slush in the bag rapidly warms, it is hard to ensure cooling at the same tem- perature and hypothermia using ice-slush method leads to renal injury.(6) In order to cool the cortex with ice-slush, a volume of about 300–750 cc is re- quired. This leaves 5–20min of time to manipulation. Besides, 15min should be al- lowed to the kidney to cool down. This procedure leads to loss of temperature in the tissues in the vicinity of the kidney, contacting with the ice-slush.(2) Retrograde endoscopic renal hypothermia is yet another method of hypother- mia. Cold salina is cooled down to −1.7◦C and is circulated by the retrograde ure- thral route. Cooling of the kidney within the classical ice bag decreases the temper- ature in the cortex. Researchers compared and contrasted ice-cold saline circulated by retrograde urethral instrumentation and traditional ice-slush cooling methods after renal artery occlusion.(7) One of the studies aiming to provide an effective hypothermia on the renal cortical surface is the external cooling device to the kidney study conducted by Cockett in 1961.(8) In the concerned method, the kidney is completely mobilized and a rougher device is placed outside the kidney. The kidneys are totally mobilized in the ice-slush method and in Cockett’s method and this affects the operation time. A time of 10–15 min is needed for the cooling down of the kidney and unchanging hypothermia cannot be provided to all parts of the kidney in the ice-slush method.(9) Wakabayashi et al.(10) introduced the technique that ice-slush can be inserted easily into the retroperitoneal space through any cylindrical device about 3 cm in diameter by enlarging the primary port site. The major aim of this study was to be able to maintain the targeted temperature value at a certain part of the kidney and to develop a non-invasive renal hypother- mia system to create an ideal hypothermia. DESIGNED SYSTEM In the present study, a renal hypothermia system controlled by a microcon- troller is designed and manufactured. Block schema of the developed system is pre- sented in Fig. 1. Temperature value in the system is controlled by using 8-byte microcontroller, PIC16F877, and programmed by microcontroller MPASM package. The tempera- ture value obtained from sensors output, feeds the microcontroller PIC16F877. A 10-byte counter that can be adjusted as four ups–downs separately between 0 and 700 is placed in PIC16F877 in order to determine the temperature value at different parts of the kidney. Thus, not only the temperature value of the area can be adjusted by its own counter, but also the thermoelectric module and the sensors that perceive the temperature of these modules can be selected. Thermoelectric Renal Hypothermia System 443 Fig. 1. Block schema of the developed system. Microcontroller calculates the difference between the adjusted temperature value and the real temperature value. The difference is multiplied by the system’s proportional gain. The proportional tension obtained in this way is used as the con- trol tension that changes duty cycle of the Switch Mode Power Supply (SMPS). When the control tension of SMPS is proportionally altered, the outlet tension au- tomatically changes proportionally. This tension feeds the thermoelectric module in the selected area. The system is equipped with a continuous cycle, required for cooling in thermoelectric systems. A serpentine formed from a 4-mm copper tube is mounted at the opposite side of the module’s surface cooling the kidney. Water at room temperature is pumped through a plastic pipe to the serpentine, which travels along the serpentine and re- turns to the depot. Thus, temperature of the part of the module that functions as a cooler is stably controlled. In case that there is not sufficient water in the sys- tem or in case of sensor errors, alarm system is automatically activated and gives a sonorous warning. In addition, the type of the error can be monitored from the Liquid Crystal Display (LCD). When the temperature value in the system reaches or exceeds the warning limit, alarm system is activated. The system can readily pro- vide the ideal temperature value of hypothermia, which is 15◦C, in 15min and the temperature range can be adjusted between −50 and +50◦C. When the tempera- ture of a module reaches the desired cooling value, the system can maintain the same temperature value for as long as necessary. The flow chart of the program is shown in Fig. 2. The flow chart is shown in this figure in a general approach with the subroutines. The main body of the system covers an area of 50 cm × 25 cm × 25 cm. Each module is square in shape and 4 cm × 4 cm × 0.3 cm in size. It can be used in the form of a box that can house renal poles depending on the modular position. Schematic view and application of the developed renal hypothermia system is pre- sented in Fig. 3. 444 Is¸ik Fig. 2. The flow chart of developed control system. RESULT AND DISCUSSION Performance analysis of the microcontroller controlled hypothermia system re- alized in this project is measured by Gazi University Technical Education Faculty Thermoelectric Renal Hypothermia System 445 Fig. 3. External view of the developed system. Electronics and Computer Education Department’s Research and Development Laboratories through a 60-min test. It is found that optimal renal hypothermia temperature is 15◦C with the exper- iments performed by Ward.(1) For this purpose, system temperature was adjusted to 15◦C, and measurements were repeated every 5 min and every measurement was also repeated 10 times and their arithmetic mean is calculated. Obtained results are given at Table I and shown in Fig. 4. As for surface hypothermia obtained with ice-slush, it is difficult to keep the cortical temperature at the same value since the ice-slush warms up very rapidly. Besides, there is a loss of temperature in the tissues in the vicinity of the kidney, as 15min should be allowed the kidney to cool down. Arterial occlusion at 20◦C provided an operation time of up to 2 h in practice and this time were extended up to 4 h in some cases by opening and closing the artery. In the external cooling device to the kidney devised by Cockett to ensure an effective hypothermia on renal cortical surface, the kidney is completely mobilized and a rougher device is placed outside the kidney. Table I. 15◦C Cooling Test Results of Developed Renal Hypothermal System Time (min) Module temperature (◦C) 0 26.7 5 14.9 10 15.2 15 14.8 20 15.3 25 15.1 30 14.9 35 15.1 40 15.3 45 15.2 50 15.2 55 15.1 60 15.2 446 Is¸ik Fig. 4. +15◦C adjusted temperature variation graph of system. The kidneys are entirely mobilized in the ice-slush method and Cockett’s method. This affects the operation time, since about 10–15min should be allowed the kidney to cool down. Besides, ice-slush does not bring about an unchanging hy- pothermia in all parts of the kidney. Recent studies in the field of renal surgery aim at finding a bloodless, long- lasting method that does not result in renal dysfunction. This can be achieved by working in a hypothermic environment. In this study, it was planned to develop a non-invasive renal hypothermia sys- tem that could keep a targeted part of the kidney at a certain temperature for as long as necessary. Thanks to this system, renal cortex can be cooled down to the intended temperature values, totally or locally, and the temperature of the cooling module reaches the level of application in as shortly as 3min. Since the parts of the module not used for cooling are isolated, it does not have any influence on the body temperature or the tissues around the kidney. Cooling modules can be used in two opposite sides of the kidney at the same time. After the temperature of the module reaches the targeted cooling value, the same temperature can be stably maintained. It is contemplated that the system not only does not prolong the operation time, but also confers all the advantages of hypothermia. The developed renal hypothermia system brings any part of the kidney to the targeted temperature in 5min and reliably maintains that temperature value for the determined period of time. No significant temperature changes take place in other parts of the kidney and general body temperature is not affected, either. In short, it was seen that the system could simply ensure extra renal hypothermia in the targeted way. If compared to the previously applied methods, the differences of designed and realized renal hypothermia system in this study are arranged below. System usage is easy and able to reach to the desired temperature in 5 min. Additionally, it does not affect body temperature and does not effect to the tissues around kidneys. If desired, only the area of interest is cooled and can be mobilized independent of other areas. Cooling modules can be used both sides of kidney surface at the same time. Thermoelectric Renal Hypothermia System 447 Modules can be sterilized ethylene oxide gas. Dimensions of module are 4 cm × 4 cm × 0.2 cm and its shape is a square. Depending on the position, it can be used inside a box enclosing renal poles. The temperature of the module can be stabilized after it reaches aimed cold- ness. The bulk of system has a volume dimension of 50 cm × 25 cm × 25 cm. It does not need any extra spending and expenditure supplies. System does not increase operation period, and also offers all the advantages of hypothermia. It can easily provide the ideal hypothermia temperature of 15◦C in very short time. Handling of module inside the body is very easy. Because of the isolation of the parts that are not in use, of the module, tissues behind the modules will not cool. System can be used by trans-peritoneal approach. System also provides con- tinuous temperature measurements without any hardship and time waste. 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