Deniss Karai

Continuous blood pressure monitoring during exercise using pulse wave transit time measurement

This paper gives an overview of a research, which is focused on the development of the convenient device for continuous non-invasive monitoring of arterial blood pressure. The blood pressure estimation method is based on a presumption that there is a singular relationship between the pulse wave propagation time in arterial system and blood pressure. The parameter used in this study is pulse wave transit time (PWTT). The measurement of PWTT involves the registration of two time markers, one of which is based on ECG R peak detection and another on the detection of pulse wave in peripheral arteries. The reliability of beat to beat systolic blood pressure calculation during physical exercise was the main focus for the current paper. Sixty-one subjects (healthy and hypertensive) were studied with the bicycle exercise test. As a result of current study it is shown that with the correct personal calibration it is possible to estimate the beat to beat systolic arterial blood pressure during the exercise with comparable accuracy to conventional noninvasive methods.

Effect of low frequency modulated microwave exposure on human EEG: individual sensitivity.

The aim of this study was to evaluate the effect of modulated microwave exposure on human EEG of individual subjects. The experiments were carried out on four different groups of healthy volunteers. The 450 MHz microwave radiation modulated at 7 Hz (first group, 19 subjects), 14 and 21 Hz (second group, 13 subjects), 40 and 70 Hz (third group, 15 subjects), 217 and 1000 Hz (fourth group, 19 subjects) frequencies was applied. The field power density at the scalp was 0.16 mW/cm(2). The calculated spatial peak SAR averaged over 1 g was 0.303 W/kg. Ten cycles of the exposure (1 min off and 1 min on) at fixed modulation frequencies were applied. All subjects completed the experimental protocols with exposure and sham. The exposed and sham-exposed subjects were randomly assigned. A computer also randomly assigned the succession of modulation frequencies. Our results showed that microwave exposure increased the EEG energy. Relative changes in the EEG beta1 power in P3-P4 channels were selected for evaluation of individual sensitivity. The rate of subjects significantly affected is similar in all groups except for the 1000 Hz group: in first group 3 subjects (16%) at 7 Hz modulation; in second group 4 subjects (31%) at 14 Hz modulation and 3 subjects (23%) at 21 Hz modulation; in third group 3 subjects (20%) at 40 Hz and 2 subjects (13%) at 70 Hz modulation; in fourth group 3 subjects (16%) at 217 Hz and 0 subjects at 1000 Hz modulation frequency.

Pulse Wave Velocity in Continuous Blood Pressure Measurements

This paper is a part of research which is focused on the development of the convenient device for continuous non-invasive monitoring of arterial blood pressure by noninvasive and non-oscillometric way. Potentially useful parameter for continuous monitoring of blood pressure could be the pulse wave velocity between different regions of human body. It has been demonstrated that systolic blood pressure estimation from this parameter is possible with acceptable accuracy by personal calibration of the method for particular patient. However, most of previous studies are focused on utilizing such measurement on patients in critical conditions; the data of experiments with healthy subjects are quite limited. The blood pressure estimation method is based on a presumption that there is a singular relationship between the pulse wave velocity in arterial system and blood pressure. The measurement of pulse wave velocity involves the registration of two time markers, one of which is based on ECG R peak detection and another on the detection of pulse wave in peripheral arteries. As a result of current study it is shown that with the correct personal calibration it is possible to estimate beat-to-beat systolic arterial blood pressure with comparable accuracy to conventional noninvasive methods.

Effect of Microwave Radiation on Human EEG at Two Different Levels of Exposure

This study is aimed at evaluating the effect of microwave radiation on human brain bioelectric activity at different levels of exposure. For this purpose, 450 MHz microwave exposure modulated at 40 Hz frequency was applied to a group of 15 healthy volunteers at two different specific absorption rate (SAR) levels: a higher level of 0.303 W/kg (field strength 24.5 V/m) and a lower level of 0.003 W/kg (field strength 2.45 V/m). Ten exposure cycles (1 min off and 1 min on) at fixed SAR values were applied. A resting eyes-closed electroencephalogram (EEG) was continuously recorded. Results showed a statistically significant increase in the EEG power in the EEG beta2 (157%), beta1 (61%) and alpha (68%) frequency bands at the higher SAR level, and in the beta2 (39%) frequency band at the lower SAR level. Statistically significant changes were detected for six individual subjects in the EEG alpha band and four subjects in the beta1 and beta2 bands at the higher SAR level; three subjects were affected in the alpha, beta1 and beta2 bands at the lower SAR level. The study showed that decreasing the SAR 100 times reduced the related changes in the EEG three to six times and the number of affected subjects, but did not exclude the effect.

Effect of noise in processing of visual information

Background Information transmission and processing in the nervous system has stochastic nature. Multiple factors contribute to neuronal trial-to-trial variability. Noise and variations are introduced by the processes at the molecular and cellular level (thermal noise, channel current noise, membrane potential variations, biochemical and diffusion noise at synapses etc). The stochastic processes are affected by different physical (temperature, electromagnetic field) and chemical (drugs) factors. The aim of this study was experimental investigation of hypotheses that increase in the noise level in the brain affects processing of visual information. Change in the noise level was introduced by an external factor producing excess noise in the brain. Methods An exposure to 450 MHz low-frequency modulated microwave radiation was applied to generate excess noise. Such exposure has been shown to increase diffusion, alter membrane resting potential, gating variables and intracellular Calcium efflux. Nine healthy volunteers passed the experimental protocol at the lower (without microwave) and the higher (with microwave) noise level. Two photos (visual stimuli) of unfamiliar, young male faces were presented to the subjects, one picture after another. The task was to identify later the photos from a group of six photos and to decide in which order they were presented. Each subject had a total of eight sessions at the lower and eight at the higher noise level. Each session consisted of 50 trials; altogether a subject made 800 trials, 400 at the lower and 400 at the higher noise level. Student t-test was applied for statistical evaluation of the results. Results Correct recognition of both stimuli in the right order was better at the lower noise level. All the subjects under investigation showed higher numbers of right answers in trials at the lower noise level. Average number of correct answers from n=400 trials with microwave exposure was 50.3, without exposure 54.4, difference 7.5%, p<0.002. No difference between results at the lower and the higher noise level was revealed in the case of only partly correct or incorrect answers. Conclusions Our experimental results showed that introduced excess noise reduced significantly ability of the nervous system in correct processing of visual information.

Accurate Dialysis Dose Evaluation and Extrapolation Algorithms During Online Optical Dialysis Monitoring

The aim of this study was to propose an improved method for accurate dialysis dose evaluation and extrapolation by means of Kt/V from online UV-absorbance measurements for real time and continuous treatment monitoring. The study included a total of 24 treatments from ten uremic patients, seven of whom were male and three females. All patients were on chronic thrice-weekly hemodialysis therapy. The study included both stable and unstable treatments. A known signal processing algorithm, Levenberg-Marquardt, and the newly developed SMART were utilized for the removal of disturbances not relevant for dialysis dose evaluation. Finally, the results were compared with the Kt/V values based on the blood samples. The new data processing algorithm, SMART, removes disturbances, helps estimate the online Kt/V with significant precision increase and without any time delay, and more effectively predicts the end Kt/V for the treatment than the known algorithms.

Arterial Pulse Transit Time Dependence on Applied Pressure

Arterial pulse transit time dependence on applied pressure is analyzed experimentally. The pressure was applied on brachial artery. Pulse transit times between left and right hand were compared by calculating the correlation on different applied pressures. In addition the pulse transit time characteristics were analyzed on different pressures. It revealed that pulse transit time is not influenced by applied pressure, when it is lowered to certain level. The level can be located from piezoelectric signal amplitude.

Method of optical self-mixing for pulse wave transit time in comparison with other methods and correlation with blood pressure

This paper is a part of research to develop convenient method for continuous monitoring of arterial blood pressure by non-invasive and non-oscillometric way. A simple optical method, using self-mixing in a diode laser, is used for detection of skin surface vibrations near the artery. These vibrations, which can reveal the pulsate propagation of blood pressure waves along the vasculature, are used for pulse wave registration. The registration of the Pulse Wave Transit Time (PWTT) is based on computing the time delay in different regions of the human body using an ECG as a reference signal. In this study, the comparison of method of optical self-mixing with other methods as photoplethysmographic (PPG) and bioimpedance (BI) for PWTT is done. Also correlation of PWTT, obtained with different methods, with arterial blood pressure is calculated. In our study, we used a group of volunteers (34 persons) who made the bicycle exercise test. The test consisted of cycling sessions of increasing workloads during which the HR changed from 60 to 180 beats per minute. In addition, a blood pressure (NIBP) was registered with standard sphygmomanometer once per minute during the test and all NIBP measurement values were synchronized to other signals to find exact time moments where the systolic blood pressure was detected (Korotkoff sounds starting point). Computer later interpolated the blood pressure signal in order to get individual value for every heart cycle. The other signals were measured continuously during all tests. At the end of every session, a recovery period was included until persons NIBP and heart rate (HR) normalized. As a result of our study it turned out that time intervals that were calculated from plethysmographic (PPG) waveforms were in the best correlation with systolic blood pressure. The diastolic pressure does not correlate with any of the parameters representing PWTT. The pulse wave signals measured by laser and piezoelectric transducer are very similar and do not have any qualitative differences. Since the detection of pulse wave by piezoelectric transducer is less complicated than laser detection, the piezo transducer should be preferred in such cases, but advantage of optical method of measurement is absent of any mechanical influence to artery.

Ventricular repolarization evaluation from surface ECG for identification of the patients with increased myocardial electrical instability

In order to reveal the possible correlation between the level of myocardial electrical instability assessed at Holter monitoring and certain ECG parameters characterizing ventricular repolarization 24-hours ECG recordings were analyzed in 91 patients with different grades of ventricular arrhythmias. The following parameters were calculated: RT-interval (RT) duration and variability, RT apex interval (RTa) duration and variability, areas of the first and second half of T-wave (S1, S2) and maximal rise and fall slopes of T-wave (k1, k2). An original signal processing algorithm for ECG was developed for that purpose. The results of the study suggest that complex analysis of certain T-wave parameters, as well as RT interval variability can be a useful tool for identification of patients at increased risk of sudden death.

Activity classification for real-time wearable systems: Effect of window length, sampling frequency and number of features on classifier performance

The aim of this study was to evaluate how the physical activity classification window length, accelerometer sampling frequency and the number of correlating features affect the classifier performance. It is important to study the effect of these elements in order to reduce the computational power and memory buffers needed for wearable systems, where classification is done in real-time. Three different window lengths (5 s, 3 s, 1s), sampling frequencies (50 Hz, 25 Hz, 13 Hz) and two feature sets (110 and 43 features) were tested and evaluated in this study. As a result, it was found that the classifier performed similarly with the window lengths of 5 s and 3 s and the sampling rates of 50 Hz and 25 Hz, but the results with the window length of 1 s or the sampling rate of 13 Hz were lower. No noticeable difference in classifier sensitivity was found by decreasing the number of features based on correlation.