PubMed Health⌕ Search

Biomedical subjects

N A Shaw

Publications and source records attributed to N A Shaw.

65 records · Page 4Linked to original sources
PubMed1981

The effect of pentobarbital on central somatosensory conduction time in the rat.

Somatosensory evoked potentials (SEPs) were recorded from skull electrodes in the rat. Central somatosensory conduction time was estimated by subtracting the peak latency of component II which is generated from the dorsal column nuclei and medial lemniscus from that of the primary cortical response. The mean was 2.67 +/- 0.10 msec during light pentobarbital anaesthesia. SEPs recorded during moderate anaesthesia showed delays of nearly 1 msec in anterior component III from the thalamus and sensory radiation, and the subsequent cortical potentials.

Animals↗
PubMed1979

Central somatosensory conduction time in comatose patients.

Somatosensory conduction time between the dorsal column nuclei and the cerebral cortex may be measured following median nerve stimulation by recording evoked potentials from both scalp and neck. Central conduction times were significantly increased relative to normal (5.6 +/ 0.5 msec) in 11 of 24 comatose patients. Results within 10 and 35 days of onset of coma were correlated with the final clinical outcome. Conduction times were independent of serum phenobarbital (0 to 630 mumol per liter) and of central body temperature (35.0 to 38.5 degrees C). Serial studies in coma demonstrated (1) short-term increases during temporary metabolic disorders, and (2) sustained increases with gradual recovery over many months, particularly after head injury.

Adolescent↗
PubMed1978

Effects of luminance on the pattern visual evoked potential in multiple sclerosis.

Pattern visual evoked potentials (PVEPs) were recorded at 5 levels of luminance from 26 patients with multiple sclerosis and from age-matched normal subjects. In normal subjects, the latency of both the major positive peak (P100) and the early positive peak (P60) was an inverse logarithmic function of pattern luminance. The increase in latency per unit log decrease in luminance was 12.1 msec for P100 and 5.7 msec for P60. Only 2 patients had entirely normal results. In 9 patients, the increase in latency of P100 per unit log decrease in luminance was abnormal. Of the 18 luminance-latency functions obtained from testing both eyes, 10 were abnormal, 6 showing a greater than normal increase in latency with decreasing luminance and 4 a less than normal increase. The 6 luminance-latency functions with a greater than normal increase in latency with decreasing luminance were all from patients without other evidence of optic nerve involvement. Pattern luminance, therefore, as well as patient selection, can significantly affect the proportion of abnormal PVEP latencies in any group of patients with possible, probable or definite multiple sclerosis. The abnormal response of the PVEP to changes in luminance and the different effects upon P100 and P60 indicate that the delayed PVEPs in patients with multiple sclerosis cannot be attributed solely to slowing of conduction in the optic nerve.

Adolescent↗
PubMed1977

Cerebral monitoring by compressed spectral array.

Application of a frequency analysis technique, the compressed spectral array (CSA), permits the display of cerebral activity recorded by the electroencephalogram (EEG) over long periods of time in a succinct, graphic manner. This report is a description of a system which is being developed to investigate long-term monitoring of the EEGs of critically ill patients. The computer-based methodology which has been used to implement this system is described, with illustrations of CSA-transformed EEGs.

Adult↗
PubMedDate not supplied

The brainstem auditory evoked potential: effects of high frequency filtering.

The effects of low pass filtering on the brainstem auditory evoked potential (BAEP) were studied in the lightly anaesthetised rat. The high pass filter was kept fixed at 100 Hz in order to exclude the slow components on which the four fast waves of the BAEP are superimposed. The cut-off frequency of the low pass filter was systematically raised from 160 to 32 k HZ. With a band pass of 100-160 Hz, the BAEP waveform could barely be discerned. With a bandpass of 100-320 Hz, all four BAEP waves were apparent but of diminutive amplitude. With subsequent increases in the high frequency cut-off, the BAEP waveform became more clearly defined with increases in the amplitudes and decreases in the latencies of all four waves. However, beyond 8 k Hz, there was little additional change in waveform morphology. With widening of the bandpass, there was only a small concomitant decrease in brainstem transmission time. This implies that the effects of low pass filtering acted in a basically uniform manner on all four BAEP waves.

Animals↗