Electroencephalography and clinical neurophysiology
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Electroencephalogr Clin Neurophysiol · Aug 1991
Predicting outcome in hypoxic-ischemic coma. A prospective clinical and electrophysiologic study.
A prospective analysis of 40 patients with hypoxic-ischemic coma lasting at least 6 h following sudden cardiac arrest was undertaken. The patients, all of whom had preserved brain-stem function, were studied electrophysiologically with electroencephalography (EEG), and median nerve somatosensory evoked potentials (SEPs) within 48 h to establish prognostic indices. Our results indicate that preserved brain-stem function does not necessarily predict favorable outcome following cardiac arrest as 26 of 40 (65%) patients died without awakening. ⋯ Patients with normal or delayed central conduction time (CCT) as well as 'benign' or 'uncertain' EEG findings had an uncertain prognosis as some entered a persistent vegetative state (PVS) or died without awakening. Fourteen patients (35%) awakened of whom 5 (13%) recovered completely while another 9 (23%) had varying degrees of motor or cognitive impairment. SEP and EEG findings did not distinguish between these outcomes.
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Electroencephalogr Clin Neurophysiol · Jul 1991
Comparative StudyLaser-evoked brain potentials in patients with dissociated loss of pain and temperature sensibility.
Brief heat stimuli, elicited by a CO2 laser (10.6 microns wave length), activate the most superficial cutaneous nerve terminals of the thin myelinated A delta and unmyelinated C fibres which mediate heat and pain sensations. This paper investigates late cerebral potentials (SEPs) in response to laser pulses in comparison with those to conventional electrical stimulation in 18 patients with a dissociated sensory deficit (intact mechano-sensibility and disturbed temperature and pain sensation). Patients were stimulated in the most disturbed limb (affected area) and in a corresponding control area. ⋯ Highest correlations between sensory deficits and abnormal SEPs were found in all those patients in whom computer tomography or MR imaging documented a localized destructive process in the CNS. All patients with the smallest SEP modulations despite a considerable sensory deficit had an inflammatory aetiology. Preliminary criteria to define a laser-evoked SEP as pathological are discussed.
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Electroencephalogr Clin Neurophysiol · May 1991
Direct recording of somatosensory evoked potentials in the vicinity of the dorsal column nuclei in man: their generator mechanisms and contribution to the scalp far-field potentials.
Somatosensory evoked potentials (SEPs) in the vicinity of the dorsal column nuclei in response to electrical stimulation of the median nerve (MN) and posterior tibial nerve (PTN) were studied by analyzing the wave forms, topographical distribution, effects of higher rates of stimulation and correlation with components of the scalp-recorded SEPs. Recordings were done on 4 patients with spasmodic torticollis during neurosurgical operations for microvascular decompression of the eleventh nerve. The dorsal column SEPs to MN stimulation (MN-SEPs) were characterized by a major negative wave (N1; 13 msec in mean latency), preceded by a small positivity (P1) and followed by a large positive wave (P2). ⋯ The latencies of P1 and N1 increased progressively at more rostral cervical cord segments and medulla, but that of P2 did not. A higher rate of stimulation (16 Hz) caused no effects on P1 and N1, while it markedly attenuated the P2 component. These findings suggest that P1 and N1 of MN-SEPs, as well as P1' and N1' of PTN-SEPs, are generated by the dorsal column fibers, and P2 and P2' are possibly of postsynaptic origin in the respective dorsal column nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)
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Electroencephalogr Clin Neurophysiol · Apr 1991
Randomized double pulse stimulation for assessing stimulus frequency-dependent conduction in injured spinal and peripheral axons.
Injury compromises the ability of axons to conduct action potentials at high frequencies. To study stimulus frequency-dependent conduction in injured spinal and peripheral axons, we developed a new stimulation paradigm which applies trains of double pulses at 5 Hz and randomly varied interpulse intervals of 3, 4, 5, 8, 10, 30, 50, and 80 msec. In each double pulse, the first pulse was used to condition the response activated by the second test pulse. ⋯ Spinal cord injury did not affect the dorsal root responses. L5 root compression injury depressed dorsal root action potentials at 3-5 msec interpulse intervals (36.9 +/- 8.4%, n = 4, P less than 0.0001) but had no other effect on the responses. Our data indicate that randomized double pulse evoked potentials are sensitive detectors of acute axonal dysfunction and can be used to quantify stimulus frequency-dependent conduction deficits in injured central and peripheral axons.
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Electroencephalogr Clin Neurophysiol · Mar 1991
Distribution of lumbar spinal evoked potentials and their correlation with stimulation-induced paresthesiae.
In 7 awake patients with neuropathic lower extremity pain, spinal somatosensory evoked potentials (SEP) were elicited from the non-painful leg by electrical stimulation of the peroneal nerve and mechanical stimulation of the hallux ball. Recording was made epidurally in the thoraco-lumbar region by means of an electrode temporarily inserted for trial of pain-suppressing stimulation. In response to peroneal nerve stimulation, two major SEP complexes were found. ⋯ An attempt was made to record the antidromic potential in the peroneal nerve elicited from the dorsal columns by epidural stimulation. The antidromic response was, however, very sensitive to minimal changes of stimulus strength and body position of the patient, and was also contaminated by simultaneously evoked muscular reflex potentials. Thus, peripheral responses evoked by epidural stimulation appeared too unreliable to be useful for the permanent implantation of a spinal electrode for therapeutic stimulation.