Spectral analysis of the EEG in hepatic encephalopathy treated with levodopa

Methods for diagnosing hepatic encephalopathy in patients with cirrhosis: a multidimensional approach

There is no "gold standard" for diagnosing hepatic encephalopathy in patients with cirrhosis. In consequence, the presence of this condition, unless floridly overt, is often missed. As a result, the majority of patients are denied the benefits of treatment. There are a number of individual techniques, which access different aspects of cerebral function that can be used, singly or in combination, to provide diagnostic information in this condition, including mental state assessment, psychometric testing, electroencephalography, sensory and cognitive evoked potentials, and neuroimaging. These have been variously applied to the study of hepatic encephalopathy but fundamental differences in the essential aims of the studies, as well as differences in the patient populations and the acquisition and analysis of the data, have made comparisons difficult. Thus, there is no clear consensus as to the sensitivity, specificity, or validity of these tests when used alone or in combination. There are, however, a number of additional methods that could be used to analyze the electrophysiological data, and a number of alternative evoked potentials that could be measured to provide better diagnostic information. In addition, there are a number of techniques, such as critical flicker frequency and smooth pursuit eye movements, which have not yet been applied systematically in this condition and which may provide useful diagnostic information. Clearly the methods for assessing hepatic encephalopathy need to be reviewed, newer methods for analyzing the electrophysiological data and newer techniques for assessing alternative aspects of cerebral function need to be explored for their diagnostic utility. This process should aim at developing a multidimensional diagnostic tool.

An investigation of the relationship between the liver and brain using an isolated perfused rat brain preparation

The pathogenesis of portal-systemic encephalopathy (PSE) and hepatic encephalopathy (HE), disorders of the brain attributed to abnormal liver function, are poorly understood. This study was conducted to examine if a fundamental, and possibly exclusive, homeostatic interrelationship exists between the liver and brain that might deteriorate during liver failure to result in the syndrome of PSE and HE. An isolated organ perfusion circuit was devised to accommodate an isolated rat brain and an isolated rat liver preparation perfused concomitantly. The survival time of the brain preparation was measured by the maintenance of the spontaneous electroencephalocorticogram and was extended from a median survival time of 35 min (range 22 to 53 min), when perfused alone, to 210 min (range 172 to 480 min), when perfused simultaneously with a liver. Also, concomitant perfusion with an isolated rat liver reduced perfusate glucose concentrations from 200 mg% to a range between 45 to 60 mg%. These data support our hypothesis that a homeostatic interrelationship exists between the liver and brain that is independent of other metabolic influences; disturbance of this relationship may contribute towards the syndrome of PSE and HE.

Brain mapping analysis in patients with hepatic encephalopathy

Topographical analysis of cerebral electrical activity was performed in 44 patients with hepatic encephalopathy. These patients were classified in 5 groups according to clinical criteria. Eight healthy subjects were used as a control group. All were studied in an awake, eyes closed, condition and some [Control Group (CG), Group 0 (G0), Group 1 (G1) and Group 2 (G2)] also in an awake, eyes open, condition. The awake, eyes closed, maps showed marked differences in the power spectral density (PSD) of the different bands, when comparing normal subjects with patients with several degrees of hepatic encephalopathy. These differences were related to the degree of clinical involvement, mainly in the alpha and delta PSD bands. The combination of a decreased alpha PSD, increased delta PSD, and decreased mean dominant frequency (MDF) allowed a clear discrimination between the different clinical groups. The differences observed between awake, eyes closed, and awake, eyes open, conditions were especially helpful to discriminate between CG subjects and G0, G1 and G2 patients.

EEG and spectral analysis in acute hyperventilation

Acute hypocapnia decreases CBF, increases hemoglobin affinity for oxygen and causes cerebral tissue hypoxia. This tissue hypoxia is reversed with inhalation of 100% O2 in dogs. EEG slowing produced by hyperventilation is considered a manifestation of cerebral hypoxia due to decreased CBF and is thought to be reversed with hyperoxia. This study evaluated the effects of 3 gas mixtures (16% O2, 21% O2, 100% O2) on posterior frequencies of the resting and hyperventilatory EEG in normal subjects aged 23-37. Hypocapnia was maintained to an end-tidal pCO2 of 21 mm Hg for 3 min. Respiratory measures, heart rate, saO2, minute ventilation and side effects were recorded. EEG was analyzed by visual inspection and by spectral analysis. Spectral analysis evaluated total amplitude, percentile frequencies, and peak frequencies. There were significant changes from eucapnia to hypocapnia for the group in all physiologic parameters, total amplitude by spectral analysis, and posterior frequencies by visual analysis. There were no significant differences among the gases. We conclude that the EEG changes of hyperventilation are independent of the concentration of inspired oxygen over the range studied in our subjects. Symptoms of hyperventilation are likewise independent of the inspired oxygen concentration for the range studied.

Objective measurement of hepatic encephalopathy in pigs by means of spectral analysis and evoked responses

Objective measurement of hepatic encephalopathy by means of spectral analysis of the electroencephalogram (EEG), visual-evoked potentials (VEP) and brainstem auditory-evoked potentials (BAEP) was studied in pigs with ischemic hepatic necrosis. The mean dominant frequency (MDF) and the relative power of the delta frequency band (% delta power) showed significant changes with increasing encephalographic grades of encephalopathy: MDF dropped from 7.0 +/- 0.5 (grade 0) to 2.7 +/- 0.3 Hz (grade 3 encephalopathy) and % delta power increased from 52 +/- 7 (grade 0) to 83 +/- 6% (grade 3). The patterns of the VEP in pigs corresponded to those of the human VEP. However, significant differences in either latency time of the peaks or the peak amplitude with increasing stages of hepatic encephalopathy could not be found. The BAEP registered for pigs were reproducible but also were not as useful as spectral analysis for grading hepatic encephalopathy.

Correlation between electroencephalogram, hepatic encephalopathy grade, and biochemical indices in beagles with portacaval anastomosis

The EEG, grades of hepatic encephalopathy, and biochemical indices of 16 beagles with portacaval anastomosis were recorded throughout their lives and correlations between these parameters were investigated. The degree of deterioration of some biochemical indices, such as the ammonia concentration, glutamate oxaloacetate transaminase and alkaline phosphatase activities in the plasma, and percentage loss of body weight showed a progressive increase parallel to the severity of the hepatic encephalopathy (HE) grade (grading scale O-IV), but other biochemical indices such as the concentrations of aromatic or branched-chain amino acids, the molar ratio of branched-chain to aromatic amino acids, or the total protein concentration in the plasma did not show such relationship. The SW ratio, an index of the incidence of slow-waves in the EEG, was calculated from frequency distribution histograms which were obtained by frequency analyses of EEG recordings. A slight but significant correlation was found between the SW ratio and the plasma ammonia concentration. In addition, the SW ratio consistently increased with increase in the HE grade, although the SW ratio in HE grade IV was below the normal range for beagles. These results show that only the ammonia concentration in the plasma correlates with deterioration of the HE grade and of the SW ratio, suggesting that changes in ammonia concentration in the plasma should be of diagnostic value in assessing changes in mental state and the EEG in patients with liver cirrhosis. The importance of ammonia in pathogenesis of HE is stressed.

Objective measurement of hepatic encephalopathy by means of automated EEG analysis

Automated analysis of the electroencephalogram as an objective measurement of hepatic encephalopathy for the individual patient was investigated. The mean dominant frequency of patients with grades 0 and 1 hepatic encephalopathy was in the normal range (greater than or equal to 6.4 Hz); grade 1 hepatic encephalopathy, however, was characterized by abnormal relative power of theta activity of more than 35%. Twelve out of 34 patients with clinical grade 0 hepatic encephalopathy also had an elevated power of theta activity and probably therefore latent hepatic encephalopathy. Patients with grades 2, 3 and 4 hepatic encephalopathy had a low mean dominant frequency (less than 6.4 Hz) and could be identified by a biphasic power spectrum (theta and delta peaks, grade 2) or by a high power of delta activity (greater than or equal to 70%, grade 3-4). We conclude that automated EEG analysis based on the parameters mean dominant frequency and the relative powers of the delta and theta band is very suitable for objective classification of hepatic encephalopathy in individual patients.