QT interval variability index and QT interval duration during different sleep stages in patients with obstructive sleep apnea.

OBJECTIVES: The aim of the study was to investigate the impact of obstructive sleep apnea (OSA) on the QT interval variability and duration in patients during different sleep stages. METHODS: Polysomnographic recordings of 28 (13 male, 15 female) patients with OSA and 30 (15 male, 15 female) patients without OSA were analyzed. The QT interval variability index (QTVI) and the corrected QT interval (QTc) analyses were performed using two awake, 3-4 non-rapid eye movement (NREM) and three rapid eye movement (REM) sleep episodes (each 300 s). The Bazett formula, linear, and parabolic heart rate correction formulas with two separate α values were used. RESULTS: QTVI was statistically higher in OSA than in non-OSA patients for males while awake (awake -0.7 ± 0.3 vs -1.2 ± 0.2, p = 0.001; NREM ‒0.9 ± 0.4 vs -1.1 ± 0.3, p = 0.110; REM ‒1.1 ± 0.3 vs -1.3 ± 0.2, p = 0.667) and for females in all wake-sleep stages (awake -0.3 ± 0.7 vs -0.9 ± 0.5, p = 0.001; NREM ‒0.3 ± 0.5 vs -0.8 ± 0.4, p = 0.002; REM -0.3 ± 0.5 vs -1.0 ± 0.4, p < 0.001). QTVI was significantly higher during awake compared to sleep stages in OSA males (p < 0.05); no difference between wake-sleep stages was found in females (p > 0.05). Significant gender differences in QTVI existed in OSA patients during sleep (p < 0.05) but not while awake. No significant differences in QTc between patients groups were observed. CONCLUSIONS: OSA is associated with increased QT variability. REM sleep per se does not increase QTVI. In OSA patients, QTVI might be a more useful measure to detect ventricular repolarization abnormality than measures of QTc.

Influence of gender on the QT interval variability and duration in different wake-sleep stages in non-sleep apneic individuals: Analysis of polysomnographic recordings.

INTRODUCTION: The aim of the study was to determine the influence of gender and sleep stages, especially rapid eye movement sleep (REM), on QT interval variability and duration in normal subjects. METHODS: Polysomnographic recordings of 24 male and 24 female patients without obstructive sleep apnea were analyzed. In each patient, the QT interval variability index (QTVI) and the corrected QT interval (QTc) values were calculated as means of 2 awake, 4 non-rapid eye movement sleep (NREM) and 3 REM episodes, 300s each. For the QTc calculation, five different correction formulas were used. RESULTS: Gender-related differences in the QT interval variability and duration were detected between all sleep stages (P<0.05). In males, mean values of QTVI while awake, in NREM and REM sleep were -1.1±0.2, -1.1±0.3, -1.3±0.2. In females, mean values of QTVI were -0.9±0.4, -0.9±0.4, and -1.1±0.3, respectively. No difference between sleep stages was detected in the mean values of QTVI and QTc in both groups (P>0.05). CONCLUSION: The results of our study demonstrate no significant overall impact of sleep stages on ventricular repolarization variability and duration during physiological sleep in both genders. We found gender differences in the mean values of QTVI and QTc during different sleep stages, which confirm that gender is a modulating factor of ventricular repolarization.

QT Interval Variability Index and QT Interval Duration in Different Sleep Stages: Analysis of Polysomnographic Recordings in Nonapneic Male Patients.

The aim of the study was to determine whether different sleep stages, especially REM sleep, affect QT interval duration and variability in male patients without obstructive sleep apnea (OSA). Polysomnographic recordings of 30 patients were analyzed. Beat-to-beat QT interval variability was calculated using QTV index (QTVI) formula. For QTc interval calculation, in addition to Bazett's formula, linear and parabolic heart rate correction formulas with two separate α values were used. QTVI and QTc values were calculated as means of 2 awake, 3 NREM, and 3 REM sleep episodes; the duration of each episode was 300 sec. Mean QTVI values were not statistically different between sleep stages. Therefore, elevated QTVI values found in patients with OSA cannot be interpreted as physiological sympathetic impact during REM sleep and should be considered as a risk factor for potentially life-threatening ventricular arrhythmias. The absence of difference of the mean QTc interval values between NREM and REM stages seems to confirm our conclusion that sympathetic surges during REM stage do not induce repolarization variability. In patients without notable structural and electrical remodeling of myocardium, physiological elevation in sympathetic activity during REM sleep remains subthreshold concerning clinically significant increase of myocardial electrical instability.

Smart photoplethysmographic sensor for pulse wave registration at different vascular depths.

The aim of this paper is to propose a smart optical sensor for cardiovascular activity monitoring at different tissue layers. Photoplethysmography (PPG) is a noninvasive optical technique for monitoring mainly blood volume changes in the examined tissue. However, different important physiological parameters, such as oxygen saturation, heart and breathing rate, dynamics of skin micro-circulation, vasomotion activity etc., can be extracted from the registered PPG signal. The developed sensor consists of 32 light emitting sources with four different wavelengths, which are located to the four different distances from four photo detectors. Compared to the existing sensors, the system enables to select the optimal LED (light emitting diode) and photo detector couple in order to obtain the pulse wave signal from the interested blood vessels with the highest possible signal to noise ratio. In this study, the designed PPG sensor was tested for the pulse wave registration from radial artery. The highest efficiency and signal to noise ratio was achieved using infrared LED (940 nm) and photo-diode pair.

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.

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.

Higuchi's fractal dimension for analysis of the effect of external periodic stressor on electrical oscillations in the brain.

This study addresses application of Higuchi's fractal dimension (FD) as a measure to evaluate the effect of external periodic stressor on electrical oscillations in the brain. Modulated microwave radiation was applied as a weak periodic stressor with strongly inhomogeneous distribution inside the brain. Experiments were performed on a group of 14 volunteers. Ten cycles (1 min on, 1 min off) of 450-MHz microwave radiation modulated at 40 Hz were applied. Higuchi's FD was calculated in eight symmetric electroencephalographic (EEG) channels located in frontal, temporal, parietal, and occipital areas. FD values averaged over a group detected a small (1-2%) but statistically significant increase with exposure in all EEG channels. FD increased for 12, decreased for one, and was constant for one subject. FD showed the most remarkable effect in temporal and parietal regions of the left hemisphere where the microwave field was maximal. Changes of FD in these regions of the right hemisphere were much higher than expected in accordance with the field distribution. Correlation of FD between different EEG channels was high and retained its value in exposed conditions. Spreading of disturbance between different brain areas is supposed to be crucial for the effect of exposure on the electrical oscillations in the brain.

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.

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.