Sex differences in age regression parameters of healthy adults--normative data and practical implications.

After appropriate transformations age regression parameters for relative band power values were determined in two groups of normal subjects (94 men and 80 women) between 20 and 70 years of age. Four homologous bipolar derivations over each hemisphere were considered. For most regression equations significant sex differences were found for the intercept values; a sex difference for the regression coefficient was only present for the temporal theta power. The use of patient and control groups composed solely of subjects of the same sex can be indicated when studying groups of subjects with minor qEEG disturbances, an example of which is given.

Electroencephalographic studies in workers exposed to solvents or pesticides.

The qEEG was studied in groups of young and old workers exposed to solvents (house and industrial painters) and in a group of workers exposed to pesticides. Three methods were used: a quantified visual scoring system, the neurometrics method and a multivariate analysis of mean frequencies. Using the visual assessment as well as the neurometrics method, the older painters showed more abnormalities than the younger painters and the pesticide exposed workers. The "profile" of abnormalities differed in all 3 groups. Changes of the mean spectral frequencies were mainly found in the subjects exposed to pesticides. In this study we concluded that the neurometrics method can be useful in neurotoxicological studies. With this technique minor changes in electrocortical function can be detected in seemingly normal workers. However, frequency parameters should be added to the power measures which are usually studied.

Neurometrics in cerebral ischemia and uremic encephalopathy.

The neurometric method as introduced by John was used to study three groups of patients with cerebral ischemia, three groups of patients with renal disease and an additional normal control group. The traditional neurometric approach was slightly modified: relative band power values were not expressed as a percentage of the total power per derivation but as a percentage of the "global power"; frequency matrices were used in addition to power matrices. From the study of the three groups of patients with one-sided supratentorial ischemia it appeared that sensitivity and specificity are completely satisfactory when using neurometrics in patients with severe ischemia in the middle cerebral artery territory studied within 48 hours of the onset of the stroke. However, in ischemia patients with less pronounced clinical signs and especially in patients without persistent neurological deficit the sensitivity is much lower. In studying dialysed and non-dialysed renal patients signs of an (often subclinical) encephalopathy could be detected in approximately 37% of all patients. Follow-up studies of the ischemia patients and the renal patients over a period of several years revealed a parallelism between clinical scores and qEEG scores in the ischemia patients; almost all qEEG improvement occurred in the first three months after the stroke. The qEEG profile of the groups of dialysed patients tended to be more or less stable over a period of several years.

Long-term clinical and neurophysiological effects of reconstructive vascular surgery for cerebral ischemia.

In a series of patients with unilateral supratentorial ischemia, clinical scores and parameters derived from computer analysis of the EEG and from measurement of the CBF were determined in the first several weeks after the stroke. Seventeen of these patients underwent a carotid-endarterectomy and 15 a STA-MCA bypass operation. Matched control patients were selected from the remaining cases. All patients, including the controls, were eligible for vascular surgery. The measurements were repeated respectively 3 months and 3 years after the first examination. Clinical improvement occurred in all groups. The degree of these clinical changes was similar for operated and non operated cases. EEG changes indicated more improvement in the cases without surgery. Finally, the CBF was remarkably stable in all patients. The overall effects of reconstructive vascular surgery on the recovery after cerebral ischemia appeared to be negligible.

Recovery from cerebral ischaemia. EEG, cerebral blood flow and clinical symptomatology in the first three years after a stroke.

In 43 patients suffering from unilateral supratentorial ischaemia the changes over an interval of 3 years in clinical score, quantified EEG (using the neurometric method) and CBF (Xenon inhalation method) were studied. The patients were examined 3 times: shortly after the onset of ischaemia and respectively 3 and 36 months after this first measurement. Three patients died from causes not related to cerebral ischaemia. In the surviving patients the EEG and clinical score improved, often dramatically; the CBF values did not change significantly. Most of the changes occurred in the first 3 months after the stroke. For the evaluation of the prognostic value of the various parameters, 2 sub-groups of patients with different outcome but comparable initial clinical scores were studied. A persistent neurological deficit was predicted by a low CBF at the first measurement. The neurometric parameters obtained from the initial EEG had no value in this respect.

Somatosensory evoked potentials in minor cerebral ischaemia: diagnostic significance and changes in serial records.

Frontal, central and parietal short and middle latency somatosensory evoked potentials (SEPs) arising after stimulation of the contralateral median nerve were studied in 10 normal adults. Stable SEPs were recorded: a frontal P21-N30 complex and an N20-P23-P28-N35-P42 complex in the centro-parietal region. The use of a chin reference electrode allowed identification of (the thalamic) P15 and N18. SEP studies of 20 patients with unilateral cerebral ischaemia were also performed, about 4 and 18 days after the stroke. In 13 out of 18 patients with a minor stroke (TIA, RIND and PNS) abnormalities of the frontal and/or parietal SEPs were demonstrated. Improvement in these SEPs occurred in 5 cases. In two patients who suffered from a major ischaemic deficit, the SEPs were highly abnormal and did not show any change in the course of time. SEP studies may be useful for the diagnosis of minor cerebral ischaemia as well as quantification of recovery; an even more important indication for this neurophysiological method might be detection of subclinical lesions in patients who have suffered from transient cerebral ischaemia even weeks before the SEP studies are carried out.