Significance of electrical brain activity in brain-stem death.

A 46-year-old man was diagnosed clinically brain dead after sustaining head trauma. The patient was in deep coma, brain nerves were unresponsive and spontaneous breathing was absent. However, EEG showed well preserved activity, but no reactivity to external stimuli. EEG activity disappeared within 40 h. BAEP were highly abnormal, flash-VEP as recorded 3 h after the diagnosis of brain stem death was of high amplitude but of simplified form. The neurophysiological findings revealed that the main reason for deep coma was brain stem damage while cortical activity was still present. This condition raises ethical questions when brain death is diagnosed clinically prior to removal of organs for transplantation.

Multi-centre comparison of five eye movement detection algorithms.

Although various investigators have suggested algorithms for the automatic detection of eye movements during sleep, objective comparisons of the proposed methods have previously been difficult due to different recording arrangements of different investigators. In this study the results of five eye movement detection algorithms applied to the same data were compared to visually scored data. The percentages of true and false detections are given for various threshold levels in rapid and slow eye movement detections. The methods gave best results when they were used with the same electrode montage they were designed for but the performance decreased when other montages were used. Subtracting the cross-talk of EEG delta activity improved the correctness of eye movement detections.

Clinical and neurophysiological observations on acute herpes zoster.

We studied 31 patients with acute herpes zoster (AHZ) less than 28 days' duration. Clinical characteristics (pain, allodynia, course of disease) and somatosensory perception thresholds (thermal discrimination, hot pain, and vibration) of the affected dermatome and the contralateral homologous area were assessed. Touch-evoked allodynia was found in 17 (55%) and dysesthesia in a further 5 (16%). Thermal and vibration perception thresholds demonstrated significant elevations when compared to the contralateral side. Thermal threshold abnormalities were significantly associated with the prevalence of postherpetic neuralgia (PHN) at 3 months. The effect of nerve blockade was less favorable on allodynia than spontaneous pain. The results of possible pathophysiological mechanisms are discussed.

Neurophysiological and technical considerations for the design of an implantable phrenic nerve stimulator.

Sequential stimulation during one muscle contraction of several compartments of a motor nerve, using multiple-electrodes, allows individual nerve-muscle compartments to be stimulated at fairly low frequencies. This provides time for recovery even during muscle contraction. However, the whole muscle is stimulated at near to its optimum fusion frequency, which provides smooth muscle contraction. This stimulation system imitates the natural activation of skeletal muscle. The new phrenic nerve stimulator described utilises the principle of sequential motor nerve stimulation. It also incorporates a sigh function. The sigh current recruits additional axons at certain intervals and thus creates and keeps available a reserve of conditioned muscle. Clinical advantages result: the conditioning phase after the beginning of long-term phrenic nerve stimulation for electroventilation is shortened and muscle fatigue is delayed. A need of increase of gas exchange can be answered by increasing tidal volume instead of respiration rate alone.

Magnetic facial nerve stimulation in Bell's palsy.

The transcranial magnetic stimulation (TMS) technique makes it possible to stimulate the intracranial part of the facial nerve. In a total of 51 patients with acute Bell's palsy, TMS was performed, and the responses were compared with those elicited by conventional extracranial electric stimulation (EES). Clinical recovery was evaluated at 258-539, mean 410, days from the beginning of the palsy. With both techniques the motor evoked potentials (MEPs) could always be elicited on the healthy side, the mean latency being 4.7 ms with TMS and 3.7 ms with EES. In the acute phase, TMS elicited MEPs on the paralyzed side in 47% of the patients, and EES in 98%. The patients with TMS elicitable MEPs during the first 4 days of the palsy had significantly better recovery than those without response (p less than 0.05). The difference in recovery between patients with or without elicitable TMS responses on days 5-8 and 9-14 was not significant. In EES, the amplitude difference between the two sides within the first 4 days was not significantly (p greater than 0.05) different. On days 9-14 the patients with a less than 80% difference between the two sides recovered significantly (p less than 0.05) better than those with a difference of greater than or equal to 80%, So, TMS may be of help in the early prognosis of Bell's palsy.

A computerized analysis system for vigilance studies.

A digital signal analysis system for vigilance studies is presented. The analysis is based on adaptive segmentation, band pass filtering, nonlinear eye movement detection and rule-based decision making. A preliminary evaluation of seven subjects falling asleep showed that the system is able to detect small vigilance fluctuations reliably.

Carbamazepine in the treatment of objective myoclonus tinnitus.

Three patients have had objective clicking tinnitus which was demonstrated by using impedance audiometry. Additionally EMG studies to localize the contracting muscle were performed, and EEG recordings to find the possible focal cortical activity. One patient had central nervous degenerative lesions. Carbamazepine was given as the treatment. The results are encouraging: in all cases the clicks have almost totally disappeared, making normal living possible. When medication was discontinued, the symptoms reappeared.

Transcranial facial nerve stimulation by magnetic stimulator in normal subjects.

Magnetic stimulation provides a new method to stimulate facial nerve transcranially. Stimulation can be directed to the intracranial part of the facial nerve, whereas the conventional electric stimuli are delivered extracranially to a more peripheral part of the nerve. Fourty healthy volunteers were examined to determine the normal responses for transcranial facial nerve stimulation. The center of the inducing coil ring was located so that its center was 3 cm posterior and 6 cm lateral to the vertex. Responses were recorded on the nasolabial fold. Latencies were 4.5 +/- 0.4 ms on both sides, being 1.1 ms longer than those elicited by electric stimulation of the nerve at the stylomastoid foramen. Amplitudes with magnetic stimuli were equal to those obtained with electric stimuli. The transcranial magnetic stimulation seems to be an accurate and promising method to examine the facial nerve.

Which structures are sensitive to painful transcranial electric stimulation?

Electric transcranial stimulation (TCS) is useful for clinical studies. It is, however, painful and not generally used for awake subjects. By means of topical anaesthesia and nerve blockades we wanted to find out which structures of the scalp and cranium are sensitive to electric TCS. Altogether 21 subjects participated in the present study. Our data show that pain experienced by the subjects during electric TCS is brought about by activation of the pain receptors in the scalp under the stimulating electrodes. Topical anaesthetic cream is incapable of attenuating this pain. The periosteum does not seem to be much more sensitive electric stimulation than rest of the scalp. Furthermore, contractions of facial and neck muscles do not seem to have a significant role in pain generation in electric TCS. Pain can be prevented if sufficiently large areas of the scalp are properly anaesthetized before stimulation by e.g. blockade of the major nerves responsible for the sensation of the stimulus area.

Distributed clinical neurophysiology.

We have developed a consultation forum for clinical neurophysiology in Finland. The system connects local digital electroencephalography (EEG) recording and analysing networks using a high-speed asynchronous transfer mode (ATM) network. Clinicians can obtain a second opinion using interactive data and video consultations or using data-only consultations. In addition, the system can be used for off-line review of pre-recorded data. During a one-month evaluation, 66 EEG recordings were made altogether in Satakunta Central Hospital and consultations were required on 12 occasions. Nine of them were data-only consultations and three were data and video consultations. A data consultation lasted 15-20 min and a data and video consultation 35-45 min. Clinically, there were numerous benefits for the hospitals. The system established a link to a centre of excellence for second opinions or continuing education. It also helped with on-duty arrangements and enabled the construction of national data banks.

Motor involvement in acute herpes zoster.

Motor involvement in acute herpes zoster is considered rare, but its incidence is unknown. In a sample of 40 patients with acute herpes zoster of varying severity, an abnormal electromyogram (EMG) (fibrillation, positive waves, high-frequency discharges) was found in 21 (53%), suggesting extension of inflammation to the anterior horn and/or anterior motor roots. In the majority of patients these changes were not confined to the segment invaded by the rash but were widespread, extending several segments cranially and caudally, and both ipsi- and contralaterally. In 5 (13%) patients these changes became more extensive on repeat EMG over a period of months. There was no association between severity of rash, pain, postherpetic neuralgia, and EMG changes. We conclude that widespread subclinical motor involvement is relatively common in herpes zoster, may last for months, and is easily detectable by EMG.

Implementation of three-dimensional EEG brain mapping.

The electroencephalogram (EEG) visualization software was developed containing two-dimensional (2D) and three-dimensional (3D) brain mapping modules. The input to the program is standard clinical individual patient data recorded using digital EEG and magnetic resonance imaging (MRI). The software utilizes several techniques, such as heuristic triangulation, ray casting, Gouraud shading, and image fusion to form multimodal 3D images. The program has been applied to the 3D visualization of various EEG signals, "cortical" EEG signals, and potential fields generated by a computer model. The developed program appears to operate efficiently and intuitively in PC/Windows environment.

Effect of gradually increasing carboxyhaemoglobin saturation on visual perception and psychomotor performance of smoking and nonsmoking subjects.

The effect of gradually increasing COHb saturation on human visuoperceptual and psychomotor performance was studied in 22 nonsmokers and 22 smokers. Each subject performed two sessions in randomized order, one during air breathing and the other during CO breathing on two separate days. Testing and COHb saturation measurement were repeated six times during each session. Gas breathing was between the test periods. The increase of COHb saturation up to 12--13 per cent units had no effect (p greater than 0,05) on perceptual speed and accuracy as measured by the Bourdon--Wiersma test. Finger tapping speed was also unaffected. Visual perception measured with critical flicker frequency (CFF) was sensitive to CO. The gradual increase in COHb saturation caused a linear decrease in CFF in the both groups. An increase of one per cent unit in COHb saturation caused significant decrease in CFF (p less than 0.001), when intraindividual changes were taken into account. During acute exposure to CO there was no difference in any test performance between the groups. During air preathing there was no difference in performance although there was a significant difference (p less than 0,001) in the COHb saturation levels. This negative finding might be due to adaptation of smokers to chronic exposure of CO because of smoking.

Somatosensory evoked potentials during isoflurane anaesthesia.

Short latency somatosensory evoked potentials (SEPs) to median nerve stimulation during isoflurane anaesthesia were recorded in 12 elective-surgery patients. The effect of isoflurane on the shape, amplitude and latency of SEPs was evaluated. SEPs were recorded at awake, 1 MAC, 1.5 MAC, at electroencephalogram (EEG) burst suppression and at continuous suppression levels. Finally, SEPs were recorded when anaesthesia was lightened back to 1 MAC. The peak latency and amplitude of the first cortical N20 wave were measured. The latencies increased with increasing isoflurane concentrations. At high concentrations only an almost monophasic N20 wave was recorded, reduced in shape and amplitude. No specific changes could be correlated with the burst suppression or suppression patterns. This suggests that EEG and SEP generators are differently affected with increasing isoflurane concentration. The results indicate that SEPs can also be recorded in drug-induced EEG suppression.

The correlation of EEG compressed spectral array to Glasgow Coma Scale in traumatic coma patients.

We have studied 20 comatose intensive care patients with head injuries and/or intracranial haemorrhage in order to compare two different monitoring methods of the central nervous system. The level of unconsciousness was followed on the Glasgow Coma Scale (GCS). EEG was monitored continuously with the compressed spectral array (CSA)-method. CSA findings were classified into six categories according to the frequency content, reactivity and the amount of isoelectricity. The patients were divided into four groups according to the outcome: well-recovered, moderately recovered, poorly recovered and dead. The prognostic value of the data obtained with the GCS method was compared with that obtained by CSA. The CSA and GCS methods give information based on different neurophysiological backgrounds. This explains why the correlation of these methods was only moderate. When combining the information received from these two methods the predictability improved. In many acute situations CSA gave information about changes in the brain function, which could not be seen in GCS. The results suggest that CSA is not only a supplementary method to GCS but also a different approach to the monitoring of an unconscious patient.