Quantification of alpha rhythm desynchronization using the acceleration spectrum entropy of the EEG

Desynchronization of the alpha rhythm is usually quantified as a loss of power in the alpha band. In this study we describe an alternative approach where desynchronization is characterized as an increase in the irregularity of the EEG signal. A new measure, the acceleration spectrum entropy (ASE), is used to quantify EEG irregularity. The ASE is the normalized information entropy of the amplitude spectrum of the second derivative of a time series. The ASE is a measure of the randomness or irregularity of a time series and ranges from 0 (straight line) to 100 (discrete random signal). The ASE was calculated for short EEG epochs under eyes closed and eyes open conditions in 15 subjects. There was a significant increase in ASE in the eyes open condition, reflecting an increase in EEG complexity. The ASE is a sensitive measure of EEG desynchronization

Nonlinear transcranial Doppler analysis demonstrates age-related changes of cerebral hemodynamics

We studied the age- and gender-related changes in complexity of arterial blood flow by analyzing the maximum velocity waveforms. Data were collected by insonation of the middle cerebral artery blood flow by a 2-MHz transcranial pulsed Doppler system. Following the paradigm of nonlinear dynamical systems or "chaos" theory, complexity is best evaluated by estimating the correlation dimension (D2) and the largest Lyapunov exponent (lambda 1). Forty healthy persons (male/female ratio: 1/1; mean age 48.6 y; range 19-86 y) were studied. No gender-related differences were observed. The age-effect showed a diminishing lambda 1 [df(1, 36) = 5.687; p < 0.022] and an increasing D2 at higher age [df(1, 36) = 4.997; p < 0.032]. The age-related decline of the lambda 1 implies a more prominent periodicity, explained by reduced fluctuations in R-R intervals and an altered gain of the baroreceptor reflex. The increased D2 might be related to more prominent vessel wall oscillations due to the increased vessel wall stiffness at higher age

Treatment of chronic tension-type headache with botulinum toxin: a double-blind, placebo-controlled clinical trial

Botulinum toxin is increasingly advocated as effective treatment in chronic tension-type headache. We conducted a randomized, placebo-controlled clinical trial to prove efficacy of botulinum toxin in chronic tension-type headache. Patients were randomly assigned to receive botulinum toxin (maximum 100 units) or placebo (saline) in muscles with increased tenderness. After 12 weeks there was no significant difference between the two treatment groups in decrease of headache intensity on VAS (-3.5 mm, 95% confidence interval (CI) -20 to +13), mean number of headache days (-7%; 95% CI -20 to +4), headache hours per day (-1.4%; 95% CI -3.9 to +1.1), days on which symptomatic treatment was taken (-1.9%; 95% CI -11 to +7) and number of analgesics taken per day (-0.01; 95% CI -0.25-0.22). There was no significant difference in patient's assessment of improvement after week 4, 8 and 12. Botulinum toxin was not proven effective in treatment of chronic tension-type headache. Increased muscle tenderness might not be as important in pathophysiology of chronic tension-type headache as hitherto believe

Preliminary report of detecting microembolic signals in transcranial Doppler time series with nonlinear forecasting

BACKGROUND AND PURPOSE: Most algorithms used for automatic detection of microembolic signals (MES) are based on power spectral analysis of the Doppler shift. However, controversies exist as to whether these algorithms can replace the human expert. Therefore, a different algorithm was applied that takes advantage of the periodicity of the MES. This so-called nonlinear forecasting (NLF) is able to detect periodicity in a time series, and it is hypothesized that this technique has the potential to detect MES. Moreover, because of the lack of prominent periodicity in both the normal Doppler signals (DS) and movement artifacts (MA), the NLF has a potential to differentiate MES from normal blood flow variations and MA. METHODS: Twenty single MES and 100 MA were selected by 2 human experts. NLF was applied to MES and MA and compared with 200 randomly chosen DS. NLF resulted in a so-called prediction value that ranges from + 1 in signals with prominent periodicity to 0 in signals that lack periodicity. RESULTS: NLF revealed that MES are more predictable than the normal Doppler signals (prediction [MES]=0.829+/-0.084 versus prediction [DS]= -0.060+/-0.228; P<0.0001). Moreover, MES are more predictable than the MA (prediction [MA]=-0.034+/-0.223; P<0.0001). No difference in prediction could be found between DS and MA. CONCLUSIONS: This preliminary report shows that MES can be separated from DS and MA by NLF. Research is needed as to whether this technology can be further developed for automatic detection of MES

Transcranial Doppler and systemic hemodynamic studies in septic shock

The present study outlines the relationship between cerebral and systemic hemodynamics in patients with septic shock. Sepsis is an immune mediated systemic disease in which the systemic vascular resistance (SVR) often decreases as a result of a Gram negative sepsis. The result is a hyperdynamic systemic circulation with redistribution phenomena in different organ systems. In order to study the effect of sepsis on cerebral vessels 20 patients with septic shock (12 men, 8 women, mean age 57.9 years) were subjected to both pulmonary artery catheter and transcranial Doppler (TCD) monitoring. The data were correlated to the APACHE II score and outcome. The study showed that cerebral mean and end-diastolic blood flow velocities (BFV) in the middle cerebral arteries significantly enhanced if the SVR-index decreases. In some patients a severely reduced SVRI (below 500 dynes.s/cm5.m2) was observed in combination with a downstroke latent steal phenomenon. TCD abnormalities were strongly related to disease severity and outcome. The increased BFV are explained by a mild vasospasm of the basal cerebral arteries. TCD appears to be a valuable tool to monitor the cerebral hemodynamics in these patients. They are particularly at risk for ischemic brain damage if they are subjected to therapeutic or spontaneous hyperventilation, which can potentially be detected by TCD

Nonlinear analysis of EEG in septic encephalopathy

Electroencephalograms (EEG) were recorded in fourteen patients who experienced a severe septic encephalopathy (SE). EEG analysis included visual inspection, spectral analysis and a recently developed nonlinear analysis (the Kaplan test). All EEGs showed decreased fast activity and an increase of slow wave activity on visual inspection. There was a nonsignificant trend of negative correlation between the spectral EEG analysis and the severity of the acute systemic illness (based on the sum score of 14 variables known as APACHE II score) (standard coefficient = -0.43, p = 0.118). However, a much more pronounced and significant negative correlation was observed between the Kaplan test and the APACHE II score (standard coefficient = -0.94, p = 0.005). The EEG abnormalities seen in these patients were independent of the sedation level. Neither the EEG parameters, nor the APACHE II score, predicted outcome. Nonlinear analysis is more powerful than spectral analysis to extract clinical relevant information from EEGs in patients who experience a severe SE. The nonlinear EEG analysis suggest that brain dynamics in SE may be characterized by a shift into a fundamentally different level of cortical information exchange which can be summarized in nonlinear terminology as a loss of deterministic structure in the EEG