Photoplethysmographic signal waveform index for detection of increased arterial stiffness.

The aim of this research was to assess the validity of the photoplethysmographic (PPG) waveform index PPGAI for the estimation of increased arterial stiffness. For this purpose, PPG signals were recorded from 24 healthy subjects and from 20 type II diabetes patients. The recorded PPG signals were processed with the analysis algorithm developed and the waveform index PPGAI similar to the augmentation index (AIx) was calculated. As a reference, the aortic AIx was assessed and normalized for a heart rate of 75 bpm (AIx@75) by a SphygmoCor device. A strong correlation (r = 0.85) between the PPGAI and the aortic AIx@75 and a positive correlation of both indices with age were found. Age corrections for the indices PPGAI and AIx@75 as regression models from the signals of healthy subjects were constructed. Both indices revealed a significant difference between the groups of diabetes patients and healthy controls. However, the PPGAI provided the best statistical discrimination for the group of subjects with increased arterial stiffness. The waveform index PPGAI based on the inexpensive PPG technology can be considered as a perspective measure of increased arterial stiffness estimation in clinical screenings.

Relationship between approximate entropy and visual inspection of irregularity in the EEG signal, a comparison with spectral entropy.

BACKGROUND: Several measures have been developed to quantify the change in EEG from wakefulness to deep anaesthesia. Measures of signal complexity or entropy have been popular and even applied in commercial monitors. These measures quantify different features of the signal, however, and may therefore behave in an incomparable way when calculated for standardized EEG patterns. METHODS: Two measures widely studied for anaesthesia EEG analysis were considered: spectral entropy and approximate entropy. First, we generated surrogate signals which had the same spectral entropy as a prototype signal, the sawtooth wave. Secondly, EEG samples where rhythmic pattern caused a peak in the power spectrum in the α-frequency band were modified by enhancing or suppressing the corresponding rhythm. RESULTS: We found that the value of spectral entropy does not, in general, correlate with the visual impression of signal regularity. Also, the two entropy measures interpret a standardized artificially modified EEG signal in opposite directions: spectral peak of increasing amplitude in the α-frequency band causes spectral entropy to increase but decreases approximate entropy when low frequencies are present in the signal. CONCLUSIONS: Spectral entropy and approximate entropy of EEG are two totally different measures. They change similarly in deepening anaesthesia due to an increase in slow activity. In some cases, however, they may change in opposite directions when the EEG signal properties change during anaesthesia. Failure to understand the behaviour of these measures can lead to misinterpretation of the monitor readings or study results if no reference to the raw EEG signal is taken.

Effects of 7 Hz-modulated 450 MHz electromagnetic radiation on human performance in visual memory tasks.

PURPOSE: The aim was to examine low-level 7 Hz-modulated 450 MHz radiation effects on human performance in visually presented neuropsychological tasks associated with attention and short-term memory. MATERIALS AND METHODS: A homogeneous group of 100 subjects (37 female, 63 male) were randomly assigned to either the exposed (10-20 min, 0.158 mW cm(-2)) or the sham-exposed group. A battery of three different tests measured attention and short-term memory. Task 1 involved alternately selecting black digits from 1 to 25 in ascending order and white digits from 24 to 1 in descending order. The time spent on the task and the number of errors were recorded and analysed. Task 2 involved viewing a picture of 12 objects during 3 s, followed by a list of 24 words. The subject was required to select words representing previously presented objects. In task 3, an array of letters in 10 rows (60 in each row) was presented, and the subject was required to identify all examples of a particular two-letter combination. RESULTS: The results of tasks 1 and 3 showed a significant increase in variances of errors (p<0.05) in the exposed versus the sham-exposed group. The results of task 2 indicated a significant decrease in errors (p<0.05) in the exposed group. CONCLUSIONS: The data provide additional evidence that acute low-level exposure to microwaves modulated at 7 Hz can affect cognitive processes such as attention and short-term memory.