Kas yorgunluğunun kompanzasyonu ve nöromüsküler bloğun bilgisayar yardımıyla izlenmesi

Abstract

Bu çalışmada kol kaslarından alınan EMG işaretlerinin median frekansları hesaplanarak kasda meydana gelen yorulmanın etkilerini giderecek bir model geliştirilmiştir. Aynı zamanda nöromüsküler blok esnasında kas yorgunluğunun etkisi yapılan deneylerle incelenmiştir. İlk olarak insan vücudu üzerindeki sinir sisteminin yapısı anlatılmış, bir hücre membranında elektriksel aktivitenin oluşumu ve bu aktivitenin sinirler boyunca nasıl yayıldığından bahsedilmiştir. Bu yayılmanın temeli şekillerle gösterilmiştir. Aynı zamanda bu bölümde sinirlerle çok yakın ilişkisi olan ve insan vücudunu tamamen sarmış bulunan kaslardan bahsedilmiştir. Kasların temel yapıları anlatılmıştır. Kasların hareketi ile oluşan elektriksel işaretlerin nasıl dedekte edildiğinden bahsedilmiştir. Bir denek seçilmiş ve kol kaslarından EMG işaretleri alınmıştır. Bu işlem, kol kasları yoruluncaya kadar devam etmiştir. Alınan EMG işaretlerinin güç spektrumları çıkarılmıştır. Sürekli kas hareketi sonunda kasların yorulması nedeniyle spektrumun genelde yüksek frekanslı bileşenlerinde bir düşme alçak frekanslı bileşenlerinde ise bir artma görülür. Frekans bileşenlerindeki bu değişim median frekansının izlenmesi ile görülebilir. Kas yorgunluğunun sonucunda EMG işaretlerinde meydana gelen değişme protezlerin kontrolünü zorlaştırmaktadır. Median frekansı kullanılarak, geliştirilen bir modelle yorgunluğun protez üzerindeki etkisi azaltılmıştır. Bu konu ile ilgili yapılan deneyler ve sonuçlar açıklanmıştır. EMG işaretlerinin anestezi alanındaki uygulamasında kas yorgunluğundan yararlanılmıştır. Anestezi uygulanan sinir sisteminin durumu ve daha sonra anesteziden kurtuluşunun biyolojisi verilmiştir. Anestezi, ameliyat sırasında hastanın kas ve sinir sistemini duyarsız hale getirmek için verilmektedir. Fakat bugün yapılan ameliyatlarda hastayı uyuşturmak için verilen ilaç miktarı doktorların tecrübesine dayalı olarak yapılmaktadır. Bazen istenmeyen sonuçlar doğmaktadır. Burada yapılan çalışma ile hastanın anestezi derinliğinin tecrübeden daha ziyade, bilgisayar ile belirlenmesi sağlanmıştır. Böylece ameliyat süresi boyunca hastanın üzerinde kullanılan ilacın etkisini belirlemek çok kolaylaşmıştır.

Muscles are the motor organs of body. All body functions like the circulation of blood, standing aganist the gravity and carrying a weigth are performed by muscular activities. The muscle fibers are controlled continuously by the peripheral nervous system. In the intact animal or human, healty skeletal muscle does not contract except in response to stimulation of its motor nerve supply. The axon of a spinal neuron supplying a muscle is divided into several branches in the vicinity of the muscle. Each single motor neuron and the muscle fibers innervated by it constitude motor unit. The action potantial recording using microelectrodes submerged into the cell has a unipolar waveform. However with the external electrodes, this action potantial produces a bipolar waveform, in human tissue, the amplitude of the action potantial depends upon the diameter of the muscle fiber, the distance between the active muscle fiber and detection site and filtering properties of electrodes. The EMG signal can be detected using a surface electrode or with needle electrodes. The amplitude of the EMG signal is depend on which type of electrode is used. Typical EMG peak to peak values are 10 mV when measured with needle electrodes and 1mV when mesured with surface electrodes. However, the amplitude of the EMG is depend on the activities of musle, where the location of electrode, types of muscle and the thickness of fat tissue between skin and muscle. The spectrum of the EMG lies mainly within the 20 - 1000 Hz band. Electromyogram signals can be considered to be a zero-mean Gaussian process.The EMG, today, has two main application. - Used as a diodnastic and clinical tool vi - Used as a control signal source for the externally powered prosthetic system. During a sustained muscle contraction, the spectrum of the myoelectric signal is undergo compression as a function of time. The frequency compression may be tracked by obtaining a continuous estimate of a characteristic frequency of the spectrum, such as the mean and median,or the ratio of low-frequency components to high-frequency components of spectrum. The ratio parameter was found to be most sensitive to conduction velocity, but was the least reliable of the three. The median frequency was the least sensitive to noise. Therefore, from a theoretical point of view, the median frequency is the preferred parameter. During a sustained muscle contraction, the amplitude of electromyographic (EMG) signals increases and the spectrum of the EMG signal shifts toward lower frequencies. These effects are due to muscular fatique and can cause problems in the control of myoelectric prostheses and in the estimation of contraction level from the EMG signal, it has been well known that the fatique effects can be explained by the conduction velocity changes during the fatique process and by the idea that the conduction velocity is linearly proportional to the median frequency of EMG signals. Hence the fatique process can be monitored by measuring the median frequency. Muscular fatique may be defined as the reduction in the force- generating capacity of the neuromuscular system that occurs during sustained activity. Much of the force loss results from biochemical changes within the muscle. The fatique of sustained maximal voluntary contraction is accompanied by a decline in the surface electromyogram (EMG). in voluntary contractions, loss of force may also result from inadequate muscle activation in addition to failure of its contractile mechanism. This reduced activation could result from either a reduced motor drive by the central nervous system, a process sometimes referred to as " central fatique " or from failure of peripheral electrical transmission. By this study a fatique compansation processor has been developed. İt uses the widely accepted power spectrum density model of EMG signals that contains the conduction velocity as a measure of fatique. The processor eliminates the increase in amplitude and the shift in frequency VII and enables consistent EMG signals to be used to control prostheses. The effects of muscle fatique can not be removed by the current filtering techniques and provide additional difficulties in EMG signal processing. The fatique compensation method which removes the muscular fatique effects. Median frequency is related to the conduction velocity by the following equation. v = ( fmed / fmo ) vo fmo is the initial median frequency when the conduction velocity is at its initial value " vo " which is normalized to a value of 1. According to above equation, the conduction velocity linearly proportional to the median frequency. Hence by monitoring median frequency change as a function of time, the change of the EMG PSD and the progression of fatique can be traced. The idea of fatique compensation is quite simple. The fatique compaensating processor scales down the amplitude of the EMG signals and decompresses the fatiqued EMG PSD to the unfatiqued EMG PSD by monitoring conduction velocity or median frequency. Below equationes represents the structure of the preprocessor. So(f) = IH(f)l2S(f) H(f) = [SQR(Vo) / SQR(v)] [ (f+fiv)(f+fhv)2 / (f+f iVo)(f+fhVo)2] where So(f), S(f) and H(f) represent the unfatiqued EMG PSD, the fatiqued EMG PSD, and the processor, respectively. The one subject was healty male, aged 26 and weights 78 kg. Tests were run in İstanbul in June. In the subject, surface myoelectric signals measurements were made during seated rest and surface electrodes were attached on arm. All hemodynamic data were acquired by a human instrumentation system developed in the Medical Electronics Laboratory of the Istanbul Technical University. The system consists of an EMG amplifier, a monitor oscilloscope, which are the units of an eight channel poligraph, a data acquisition system and a personel computer. VIM Analog/Digital converter unit of the data acquisition system was used for the experiments. This system is used with a personel computer which contains a software package for data acquisition. The system is run by an application software including signal processing algorithms, developed under the aid of the package for the tests. After the subject was attached to the system by means of the surface electrodes, the data acquisition system was configured by the operator, using the program developed. The subject was then asked to hold two kg weigt in hand. Then bring his hand up and down continouesly. When the subject was doing that the acquisition was started by the operator. Sampling was done at 1000 Hz. 2500 points of data were sampled and digital values continually were stored in a binary array opened in the buffer of the computer. This procesess were done in every one minute. After the scaling of the binary data to voltage, the real values were represented on the monitor of the personel computer. After the acceptance of values by the operator, the signal processing algorithms were run and, power spectrum of myoelectric signals were found. Median frequencies were calculated by using power spectrum of myoelectric signals.The values of the median frequencies went down. Muscle fatique could be tracked by monitoring the changes in the median frequencies of the EMG spectrum. The amplitude of electromyographic (EMG) signals are increased and the spectrum of the EMG signal is shifted toward lower frequencies. The fatique compensation method was applied to the fatiqued EMG PSD. According to value of median frequencies the fatiqued EMG PSD was converted to the unfatiqued EMG PSD. İn the second application of myoelectric signals, a device has been developed for monitoring the effects of neuromuscular blocking drugs. Neuromuscular blocking drugs, or muscle relaxants, are widely used by anesthetists for producing surgical muscle relaxation. The magnitude of neuromuscular block may be estimated by stimulating a peripheral motor nerve at the wrist and observing magnitude of electromyogram signals on the adductor pollicis muscle. The system consists of an EMG amplifier, a stimulator, a monitor oscilloscope, which are the units of an eight channel poligraph, a data acquisition system and a personel computer. Analog/Digital converter unit of IX the data acquisition system was used for the experiments. This system is used with a personel computer which contains a software package for data acquisition. The system is run by an application software including signal processing algorithms, developed under the aid of the package for the test. Stimulation and Stimulators are used widely in medical. A variety of phiysical and chemical agents can be used to stimulate excitable tissue. Electrical stimuli are the most controllable. A stimulator may be defined as a divice for producing pulses of current or voltage of controlled duration, intensity and waveform. A typical stimulator consists of a frequency-generating circuit, a waveform generating circuit, and an output circuit. The frequency- generating circuit after allows the genesis of either single.manually initiated or repetitive pulses of controlled frequency, it is the function of the output circuit to supply the current or voltaj to the electrodes on the excitable tissue. The output circuit may provide a constant voltage. A stimulator was manufactured to stimulate nerves. The main advantage of the stimulator is, the frequency of its output can be changed easly, the output amplitude of it can be changed with potansiometer, it is controlled with software program and it is praticcaly used on human with security. A nine volt accumulator drives the stimulator, it has a transformatör which is convert nine volt to two hundered fifty volt. Tests were run in Medical Faculty of Çapa in İstanbul. Surface - stimulating electrodes are placed on the wrist over the ulnar nerve and are attached to a battery-driven pulse generator, which delivers 250 volt and train of four stimulation at 2 Hz. Magnitude of eiectromyogram signals were observed on the adductor pollicis muscle. Computer calculated the ratio between the first and fourth responses of train-of-four. The ratio is used to estimate the level of block. The system has clinical potential as a trend monitor of neuromuscular function during anesthesia and surgery. It also has research potential for determining the effects of newer neuromuscular blocking drugs for comparison with presently used drugs or, alternatively, for determining the effects of blocking drugs in altered physiological states.