8031 mikrodenetleyici kontrolünün biyomedikalde uygulamaları EKG aritmi detektörü

Abstract

Çeşitli üstün özellikleri nedeniyle, her sahada giderek çok daha yaygın bir şekilde kullanılan mikrobilgisayar ve bilgisayar bağlantılı cihazlar, bioraedikal alanına da girmiştirler. En belirgin özellikleri programlanabilir olmaları sayesinde her çeşit probleme uygulanabilmekte, bio- medikal cihazlarda kullanıldıklarında, veri toplama» işleme saklama» analiz etme ve teşhis koyma gibi fonksiyonları yerine getirebilmektedirler. Bu çalışmada Intel 'in 8 bitlik mikrodenetleyici aile si MCS-51 Ailesi'nin ROM'suz üyesi olan 8031 mikrodenetle- yicisinin biomedikal sahasında kullanımı örnekler üzerinde incelenmiştir.' Ana 'konu olarak insandan alınan Elektrokardiyogram işaretlerini işleyen ve bir aritmi teşhis algoritmasından hareketle hazırlanan programı ile kalp hastalıklarının teşhisinde kullanılabilecek bir cihaz hazırlanmıştır. Aritmi detektörünün yanında bir "EKG - Aritmi Simülatörü" ve bir "Veri Toplama" cihazı da aynı konuyla ilgili olarak tasarlanmıştır. Çalışmalar sürdürülürken İstanbul Tıp Fakültesinden gelen bir istek üzerine "Monark Ergometresi Devir Sayacı", biyomedikalde bir mikrodenetleyici uygulaması olarak tez kapsamı dahilinde gerçekleştirilmiştir.

There is a rapid growth in use of computers and mic rocomputer based devices in Biomedical Engineering. Circu its and systems included microprocessors are used widely because of their lower costs, high reliabilities, and high noise immunities. Such devices are also simple to implement. They're suitable to be applied to almost every kind of subjects, also complex problems which cannot be solved by other methods. The same circuitry can be used by changing only some peripheral devices and changing the software, for different problems or to improve the featu res of devices. The evolutionary tree representing of microprocessor technology is marked by a major fork. One branch is rep resented by microprocessors which have evolved in the di rection of enlarged work widths (16 or 32 bits) and inc reasingly powerful CPUs. Another branch is represented -by microprocessors which have been combined with RAM. ROM, and various I/O facilities on a single chip, and which are commonly referred to as microcontrollers. The distinguishing charasteristic of a microcontroller chip is the inclusion, on one chip, of all the resources which permit it to serve as the controller in a device or instrument. Furthermore, to support the expansion of resources beyond what is available on the chip itself, a microcontroller may include the "hooks" to make such expansion easy. Because of their suitable characters, the area of microcontroller appications is very wide. One of them is biomedical engineering. In this study, we use an eight bit microcontroller belongs to MCS-51 Family developed by INTEL. The 8031 is ROMless version of the 8051 which is the original member of the family and is the core for all devices. Tne basic architectural structure of this core is shown in Figure 1. -vi- EXTERNAL INTERRUPTS JLL INTERRUPT CONTROL £.4K ROM W İZİ BUS CONTROL ?ra tt I_.I '_ => 128 BYTES MM 7? iz. * I/O l>ORTS M P2 PI P3 AOORESS/OATA TMER t TMERO Z> İ£ SERIAL PORT FT TXO RXO COUNTER INPUTS 27tHS1-l Figure 1: Block diagram of MCS-51 Family core The features of this core are: i 8 bit CPU Extensive Boolean processing (single bit logic) capabilities 64 K Program Memory address space 64 K Data Memory address space 128 bytes of on-chip data RAM 16 bidirectional and individually addressable I/O lines Two 16 bit Timer/Counters Full duplex UART (for serial communications with other processors or PCs) -via- - 6 source/5 vector Interrupt Structure with two priority levels - On chip clock oscillator In this study, we use 8031 to design a microcomputer based biomedical system - an Electrocardiyographic (ECG) Monitoring and Arrhythmia Detection Device. After that device has designed a normal ECG and arrhythmia simulator device and a data acquisition device was developed. During all these studies, there was a wish to a device which can count and display cycles of Anaerobic Monarc Ergometer from Medical Faculty of Istanbul University. It was also an application example of microcontroller in Biomedical Engineering area, so another device has been designed for this purpose. All of. these devices are connected to a PC through the RS-232 cable so control, parameters- -and~ata.te~ reports may be sent to each other. In another words these devices have data acquisition feature. / Because the main example df this study is ECG monitoring and arrhythmia detection system, it's necessary to have some knowledge about electrocardiography and arrhythmias. The electrical activity of the human heart can be detected on the body surface and, though quite small (about lmV), can be recorded as an electrocardiog ram (ECG). Electrocardiography began late in the nine teenth century, with the aid of capillary electrometers. By time, new techniques have been developed, and the inven tion of the Braun tube» a precursor of the modern1 oscil loscope» made it possible to visualise biopotentials with higher fidelity and in real time. Although the oscilloscope is still used in patient monitors. modern ECG machines use digital sampling techniques to produce "nonfade" or scrolling displays. The first ECG recorders employed waxed paper, and later a carbon-black-coated surface. to acquire visible and recorded copies of ECG signals. These older recorders have now been replaced by chart-paper recorders using ink, thermal, or laser-based techniques to produce permanent copies of excellent quality. Computers have had perhaps the greatest impact on ECG technology, making automatic data acquisition, analysis, and diagnosis routine. The electrocardiogram has considerable diagnostic significance and applications of ECG monitoring are diverse and in wide use. -vi 11- Any disturbance in the hearts normally rhythmic con traction is called an arrhythmia. After the heart attack, the patient will be under the care of a cardiologist. The cardiologist may gather ECGs several times a day while the patient is in the hospital. In an attempt to determine exactly what is wrong with the heart. Of course, more than just ECGs are used to make a diagnosis. But after the patient leaves the hospital, there is no monitoring at all. A few patients may be monitored with a Holter monitor, a tape recorded that the patient carries around for a day. The monitor makes a tape recording of the ECG for a 12-24 Hour period. After the recording is taken, it must be analyzed by coronary care nurses. - - Many -.pa-tieats - have. - dangerous cardiac events that occur only once every few days or even weeks. Even if the arrhythmia is captured on tape, it must be found by the coronary care nurse. The nurse's job is tedious, time consuming, and subject to a great deal of human error. There is a need for a portable arrhythmia and conduc tion disturbance monitor. It should detect arrhythmias and conduction disturbances, store samples of such arrhythmias transmit them to a central computer for display and analysis, and generate alarms. The device has a general purpose computer as its heart; therefore. it is reprog rammable, thus providing for implementation of other applications. This device must alarm on catastrophic arrhythmias that pose a direct threat to the patient's life. These include: - Extreme tachycardia - Extreme bradycardia - Sinus arrest - Ventricular fibrillation - Asystole.x- " "' "The device must also detect premonitory arrhythmias that indicate a serious threat to patient. These include: - Premature Ventricular Contractions (PVCsT - Interpolated PVCs - Bigeminy - Trigeminy - R on T phenomenon - Skipped beat - Atrial Premature Beats (APBs) Each arrhythmia must be defined- in mathematical terms so that the microcomputer has the capacity to detect it in real time. In definitions, two variables are used. RR and AR, where RR is the R-to-R interval and AR is the average of eigth R-to-R intervals. Subscripts denotes the time re lations. RR(t) is the latest R-to-R interval, RR(t-l) is the previous interval and so on. AR(t) is the average over eight R-to-R intervals, including RR(t). Therefore AR(t-l) is the previous average. Flowcharts of Arrhythmia detection algorithm» system programs in assembly language and PC programs in BASIC language are in chapters 4.4.1, 4.4.2 and 4.4.3 respectively. The arrhythmia simulator which is realised in the scope of thesis is explained in section 5. This simulator is performed to test the dedector of ECG arrhythmia and to present the laboratory insrument to the students who attend electronic and medical faculties. The instrument could drive 11 kind of arrhythmias. They are Bradycardia. Tachycardia. Ventricular Fibrillation or Asystol, Skipped Beat, PVC. R-on-T, Bigeminy. Trigeminy. Interpolated PVC and APB. The rate of arrhythmia can also be selected by user from front control panel. Data acquisition instrument is explained in section 6. By using of this instrument, the analog signs from real world are converted to digital form. These datas can be saved and examined in the memory of PC. Various sampling frequencies may be selected. But during real time pro cessing it is limited by 800 Hz. It is because of the li mitation caused by RS-232 serial interface cable and un- sufficient speed of BASIC programming language.