Derya Yilmaz

Analysis of the Doppler signals using largest Lyapunov exponent and correlation dimension in healthy and stenosed internal carotid artery patients

Nonlinear analysis techniques have been applied for many applications on the physiological systems. In this research, the largest Lyapunov exponent (LLE) and correlation dimension (CD) calculations were performed to evaluate the chaotic behaviour of blood flow obtained from the healthy and stenosed internal carotid artery (ICA) using noninvasive Doppler ultrasonography technique. The Doppler signals were taken from 30 healthy, 8 mild, 8 moderate and 8 serious degree of stenosis ICA subjects. The LLE calculation was performed by using Wolf algorithm. The Grassberger-Procaccia algorithm was used for CD analysis. The calculated LLE and CD values for stenosed ICA Doppler signals were found as significantly high compared to the values belonging to the healthy subjects. It is found that, the LLEs and CDs of stenosed ICA Doppler signals increase with the increasing of the degree of stenosis. The results show that the LLE and CD can be used for diagnosis of the ICA stenosis and to determine the degree of stenosis.

Analysis of the Mobile Phone Effect on the Heart Rate Variability by Using the Largest Lyapunov Exponent

In this study, the effects of electromagnetic fields (EMFs) emitted by GSM900 based mobile phones (MPs) on the heart rate variability (HRV) were examined by using nonlinear analysis methods. The largest Lyapunov exponent (LLE) calculation was used to evaluate the effect of MP under various real exposure conditions. Sixteen healthy young volunteers were exposed to EMFs emitted by GSM900 based MP at two levels from a very low EMF (MP at stand-by) to a higher EMF (MP at pre-ring handshaking and ringing). A blind experimental protocol was designed and utilized with consideration to the physiological and psychological factors that may affect HRV. The results showed that the LLE values increased slightly with higher EMF produced by MP (P < 0.05). This change indicates that the degree of chaos in the HRV signals increased at higher EMF compared to low level EMF. Consequently, we have concluded that high level EMF changed the complexity of cardiac system behavior, significantly.

The effect of classical Turkish musics on the autonomic nervous system

In this study, the effects of two different forms of classical Turkish music (hüseyni and saba) on the Authonomous Nerves System (ANS) are investigated. During listening these music forms, the electrocardiogram (ECG) and respiration records were made from two seperated subjects groups which are age and gender matched. These records have three periods: first period is before the listening, second is listening and third is after the listening. Heart rate variability (HRV) signal are obtained form record and power spectral densities (PSD) of HRV are estimated. According to the results of calculated parameters, both of two forms of Turkish music is cause significant differences on the very low frequency (VLF) power that is effected by hormonal and thermal control or vasomotor aktivities. The high frequency (HF) power of HRV PSDs is increase at listening the form of saba Turkish music and sympatho-vagal balance (LF/HF ratio) is shifted in dominance of parasympathetic activities.

Analysis of the mobile phone effect on the heart rate variability by the calculation of correlation dimension

In this work, the effect of the electromagnetic radiation generated by mobile phone, on the heart rate variability (HRV) has been investigated using correlation dimension calculation which is a nonlinear analysis method. The 17 volunteer subjects participated to our work and the experiment is designed as three periods and each period have 7 minutes. The electrocardiogram (ECG) signals were recorded from volunteers who are in the sitting position between the base station and mobile phone and mobile phone attached to the right ear of the subject by a bone. The mobile phone is continuously called by another mobile phone at the second period for 9 subjects and at the third period for 8 subjects, randomly. Mobile phone was open and standby condition, at the other periods. The HRV signals were obtained from ECG signals and correlation dimension analysis has been performed. The student-t test was applied to the correlation dimension values calculated from mobile phone calling and standby conditions. The correlation dimension that belongs to mobile phone calling condition is found higher than mobile phone standby condition (p≪0.05). The correlation dimension gives the minimum number of independent variables necessary to generate the system dynamics. The results show that the number of variables managed to the cardiovascular system behavior increase by reason of electromagnetic radiation generated by mobile phone.

The effects of classical and turkish music samples on the Autonomic Nervous System

In this study, 27 young and healthy subjects was listening to the classical and Turkish music samples which are believed to changeable the subjects emotional state. Their effects on Autonomic Nervous System (ANS) are investigated by using the heart rate variability (HRV) analysis which is accepted as a non-invasive indicator of ANS. The electrocardiogram (ECG) and respiration records were made before and during the listening music samples. Heart rate variability (HRV) signals are obtained form records and power spectral densities (PSD) of HRV are estimated. According to the results of calculated parameters, during the listening to classical music samples some statistically significant changes were occurred in sympathetic and parasympathetic activities of ANS. Turkish music samples were not causes significant differences on the ANS related HRV parameters.

Biopotential instrumentation set

A biological signal acquisition and processing set has been designed and realized. The set can be used in teaching basic principles in recording and analyzing biological signals. This set can be used in biomedical electronics engineering and biomedical technology laboratories. The set is especially helpful to teach how the biological signals are acquired and processed. ECG and EMG signals can be selected, amplified, filtered and transferred to the monitoring devices with this set while patient safety is provided. There are a number of connection points in the set for observing the signals at various levels. Students can make measurements at each of these steps with the connection probes outside the set. The output signals can, be observed using an oscilloscope. They can also be observed from a PC monitor with an electronic card connected to ISA bus.

Analysing of the snore sound signals with AutoRegressive modelling

Obstructive sleep apnea (OSA) is a highly prevalent disease in which upper airways are collapsed during sleep, leading to serious consequences. The aim of this work is to study apnea, hypopnea and normal snoring sounds by using the criterias that are not used before in this area. The snoring sounds which are separated from segşments, that are in case of each inspiration and expiration, after enhanced by wavelet transform method. The AutoRegressive model order of these segments are determined with Final Prediction Error and Swartz Bayesion Criterion. Autocorrelation, Loss function and energy of segments are calculated on these sounds modelled with (AR) Autoregressive Model. The results were showed that the model order and energies of segments are the highest for patients of having apnea problem, middle degree for patients of having hypopnea problem and lowest degree for the patients of having normal snoring problems. In the meantime, loss function values were different for the patients of apnea, hypopnea and normal snoring patients. Data were obtained from Gulhane Military Medical Hospital at 20 patients. Those are 4 normal snoring, 8 hyponea problem and 8 apnea problem patients.

Correlation Dimension Analysis of Doppler Signals in Children with Aortic Valve Disorders

In this study, the correlation dimension analysis has been applied to the aortic valve Doppler signals to investigate the complexity of the Doppler signals which belong to aortic stenosis (AS) and aortic insufficiency (AI) diseases and healthy case. The Doppler signals of 20 healthy subjects, ten AS and ten AI patients were acquired via the Doppler echocardiography system that is a noninvasive and reliable technique for assessment of AS and AI diseases. The correlation dimension estimations have been performed for different time delay values to investigate the influence of time delay on the correlation dimension calculation. The correlation dimension of healthy group has been found lower those found in AI and AS disorder groups and the correlation dimension of AS group has also been found higher than those found in AI group, significantly. The results of this study have indicated that the aortic valve Doppler signals exhibit high level chaotic behaviour in AI and AS diseases than healthy case. Additionally, the correlation dimension analysis is sensitive to the time delay and has successfully characterized the blood flow dynamics for proper time delay value. As a result, the correlation dimension can be used as an efficient method to determine the healthy or pathological cases of aortic valve.

The chaotic behaviour of the aortic valve blood flow

In this work, the Doppler signals obtained from the cases of the healthy and pathologic aortic valve have been studied for determining the chaotic behaviour of the aortic valve blood flow. The Doppler signals gathered from the subject groups of healthy, stenosis and insufficiency have been evaluated by using the largest Lyapunov exponent (LLE) calculation. The LLE is accepted as an indicator of the chaos. LLE is a measure of the sensitive dependence to the initial conditions of a dynamical system and its value is positive for chaotic systems. The student-t test has been applied to the results obtained from LLE calculation of subject groups. The LLE values are positive for all groups. The LLE values of the subjects suffered from aortic insufficiency and stenosis have been found higher than those found in healthy group, significantly. The results show that the chaotic behaviour of aortic valve blood flow in stenosis and insufficiency cases is higher than healthy case.

The Evaluation of the Mobile Phone Effect on the Heart Rate Variability by Lyapunov Exponent Calculation

In this work, the effect of the electromagnetic radiation generated by mobile phone calling, on the heart rate variability (HRV) has been investigated using nonlinear analysis method. The electrocardiogram (ECG) signals were recorded from 10 volunteer subjects in the sitting position for 5 minutes when mobile phone is open and standby. The process was repeated same conditions while calling the mobile phone, continuously. The largest Lyapunov exponent (LLE) calculation was performed on the HRV obtained from ECG signals. The paired student-t test was applied on the LLE values. The calculating LLE values for the calling condition of mobile phone were found higher than the values belonging to the standby condition of the mobile phone (p<0.05). The results show that the chaotic dynamics of cardiovascular system behavior increase by reason of electromagnetic radiation generated by mobile phone.