Biomedical subjects

W Knezevic

Publications and source records attributed to W Knezevic.

7 recordsLinked to original sources

PubMed1991

Saccade onset and offset lambda waves: relation to pattern movement visually evoked potentials.

The lambda (lambda) wave is an occipital EEG potential which occurs when saccadic eye movements are made against an illuminated contrast background. There is some disagreement concerning the presence of sub-components to the lambda-wave, and its relationship to visually evoked potentials. In the present study, lambda-waves were recorded with saccades of different durations (30-110 ms) and compared to VEPs associated with pattern movements of similar durations and velocity. It was found that the lambda-wave consisted of a saccade onset component with positive sub-components at 59 and 100 ms after saccade onset, and a saccade offset component with a positive potential at 74 ms after saccade offset. With small saccades of 30 ms duration or less, these components superimposed to form a single lambda-wave. In the case of pattern movement VEPs, a movement onset component of latency 110 ms following movement onset, and a movement offset component at 89 ms after movement offset, were identified. The similar behaviour of the lambda-wave and VEP under these conditions supports the view that the lambda-wave is a visually evoked potential resulting from movement of the visual field across the retina during a saccadic eye movement.

Adult↗

PubMed1987

Crossed facilitation and post-contraction depression of abductor pollicis brevis motor neurons.

Crossed facilitation of abductor pollicis brevis (APB) motor neurons by voluntary contraction of the contralateral APB was investigated using F response analysis. The integrated F response EMG showed a mean 4-fold increase during contraction. This enhancement was maintained until the onset of subjective fatigue and then declined. After isometric or isotonic contraction of the ipsilateral APB there was a significant depression of F responses with a progressive return to baseline values over a 6 minute period. The significance of the findings is discussed.

Adult↗

PubMed1986

Weakness of head turning in hemiplegia: a quantitative study.

The strength of head turning was measured in normal subjects and in patients with hemiplegia of vascular origin. In normals the strength of head turning to the two sides was not significantly different. In most patients with a cortical, capsular or high brainstem lesion the strength of head turning away from the side of the lesion was reduced. In patients with a medullary lesion the strength of head turning towards the side of the lesion was reduced. The significance of these findings is discussed in relation to the cortical control of the sternocleidomastoid muscle and other muscles involved in the movement of head turning.

Adult↗

PubMed1985

Peripheral autonomic surface potential. A quantitative technique for recording sympathetic conduction in man.

Using EMG equipment with time locked recording and standard averaging facilities we were able to record a previously poorly defined skin potential. The potential, termed by us the peripheral autonomic surface potential (PASP), was recorded from the palmar surface of the hand and the plantar surface of the foot in 30 normal subjects. The PASP usually consisted of a biphasic potential with an initial negative and a later positive peak. It was elicited by randomly timed electrical stimuli over the median nerve at the wrist. The mean palmar PASP latency was 1.52 +/- 0.13 s and the mean plantar PASP latency was 2.07 +/- 0.16 s. The mean palmar and plantar PASP amplitudes were 479 +/- 105 microV and 101 +/- 40 microV, respectively. A mean sympathetic conduction velocity was calculated to be 1.28 +/- 0.18 m/s. In 5 normal subjects a similar technique was used to record a PASP from the volar surface of the left middle finger. Iontophoresis of atropine into the skin under the recording site abolished the PASP in all subjects. Palmar and plantar PASPs were recorded in 10 diabetic patients. The amplitudes (palmar 179 +/- 158 microV, plantar 17 +/- 16 microV) were significantly reduced compared to normals (P less than 0.001). Five patients with unilateral lumbar or cervical sympathectomy were studied. The PASP was absent or markedly reduced on the side of the sympathectomy in all patients.

Adult↗

PubMed1985

Ocular and ocular motor aspects of primary thalamic haemorrhage.

As part of a correlative study of the neuro-ophthalmological abnormalities in thalamic haemorrhage, we report preliminary findings in six patients with this condition diagnosed by clinical and CT brain examinations. Five patients were middle-aged and hypertensive. Two had Horner's syndrome, and three anisocoria. Three patients had prominent mesencephalic dysfunction. There was pathological confirmation of the lesion in one case. The pathogenesis of the signs of midbrain disturbance in these patients is uncertain, but may comprise pressure, traction or hypoxia, separately or in combination. There was no positive correlation between the estimated size of the demonstrated haemorrhage and the severity of the neuro-ophthalmological abnormality.

Adult↗

PubMed1985

Peripheral autonomic surface potential: a quantitative technique for recording autonomic neural function in man.

Using EMG equipment with time-locked recording and standard averaging facilities we were able to record a previously poorly studied skin potential. The potential, termed by us by the peripheral autonomic surface potential (PASP), was recorded from the palmar surface of the hand and the plantar surface of the foot in 20 normal subjects. The PASP consisted of a biphasic potential with an initial negative and a later positive peak. The mean palmar PASP latency was 1.51 +/- 0.19 seconds and the mean plantar PASP latency was 2.09 +/- 0.24 seconds. The mean palmar and plantar PASP amplitudes were 485 +/- 100 microV and 102 +/- 45 microV respectively. A mean central sympathetic conduction velocity was calculated at 1.2 +/- 0.21 m/s. In two patients with unilateral lumbar sympathectomy the ipsilateral plantar PASP was absent in one and of considerably reduced amplitude in the other. Both palmar and plantar PASPs were absent or of reduced amplitude in five patients with diabetes mellitus. The study indicates that the PASP may prove a useful quantitative test of central and peripheral autonomic function.

Adult↗

PubMed1985

Brainstem auditory evoked responses in hereditary spinocerebellar ataxias.

Brainstem auditory evoked responses were recorded in 18 patients with spinocerebellar ataxia, seven with Friedreich's ataxia, four with late-onset cerebellar degeneration, and seven with olivopontocerebellar atrophy. All patients had normal hearing. BAERs were abnormal in 10 cases (58%). Five of the seven patients with Friedreich's ataxia (71%) had grossly abnormal BAERs with wave I only being identified. Five of the patients with olivopontocerebellar atrophy (71%) had abnormal BAERs, whereas all patients with cerebellar degeneration had normal BAERs. The results indicate abnormalities of the brainstem auditory pathways in patients with spinocerebellar ataxias and show that the test is of value in the differential diagnosis of this group of disorders.

Adolescent↗