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Biomedical subjects

S Beacham

Publications and source records attributed to S Beacham.

5 recordsLinked to original sources
PubMed1999

Near ultraviolet radiation elicits visual evoked potentials in children.

OBJECTIVE: Ultraviolet radiation can be transmitted through the ocular media, as well as stimulate the retina, in some invertebrate, vertebrate and mammalian species. This study sought to determine if near ultraviolet radiation (UV-A) can elicit visual evoked potentials (VEPs) in young humans. METHODS: VEP responses to 10 nm half-peak bandwidths of 340, 360 and 500 nm stimuli were measured in 8 children aged 7-10 years. Each VEP was based on an averaged response to 200 flashes and was recorded using a sensitivity of 250 microV (full scale) with the International 10-20 electrode placements Fz, O1, Oz, O2, and A1. Peak latencies (ms) were measured for the second negative peak, N2, third positive peak, P3, and third negative peak, N3. The amplitude (microV) between N2 and P3 was also measured. RESULTS: Each child demonstrated a VEP response to both visible and UV-A stimuli. Most VEP parameters relative to the 340 and 360 nm stimuli (P < 0.05 to P < 0.001) were significantly different from the VEP responses to the 500 nm stimulus. CONCLUSION: The results indicate that the near ultraviolet stimuli were indeed visible to the young human eye.

Child↗
PubMed1996

The effects of ultraviolet-A radiation on visual evoked potentials in the young human eye.

A recent study from this laboratory using visual evoked potentials (VEPs) demonstrated that children's eyes are capable of detecting ultraviolet radiation. The aim of this study was to compare dose-response relationships in two age groups, 6-10 years (n = 10) and 20-25 years (n = 10). Under photopic viewing conditions (550 lux), exposures of monochromatic UV-A (339 nm) and visible radiation (502 nm) were correlated to VEPs. The results demonstrate that monochromatic UV-A can elicit age and dose dependent responses in the human visual system, suggesting that the eyes of children are more responsive to UV stimuli than the eyes of young adults.

Adult↗
PubMed1996

Esophageal sensation in spinal cord-injured patients: balloon distension and cerebral evoked potential recording.

We sought to determine the esophageal sensory function in patients with a C6 or C7 spinal cord injury. A balloon was repetitively distended 10 cm above the lower esophageal sphincter in five patients and nine normal control subjects. Sensation was reported on a scale from 0 to 2 with progressive distension to pain threshold (level 2). Cortical responses were recorded from midline scalp electrodes. Blinded determinations of quality and reproducibility of the potentials were performed. All subjects experienced sensation with esophageal balloon distension. Volumes to sensation showed a trend toward a higher sensory threshold in patients but were significant only for first sensation, not pain. In all subjects, a triphasic evoked potential response consisting of a negative-positive-negative complex was noted with distension but not with sham distension. Characteristics (amplitude, latency, reproducibility, and quality) of the evoked potentials were not different in patient and control groups. These data suggest sensory pathways from the distal esophagus are intact in patients with a C6 or C7 spinal cord injury.

Adult↗
PubMed1993

Cerebral evoked potentials. A method of quantification of central nervous system response to esophageal pain.

Cerebral evoked potentials (EPs) represent a new technique for the evaluation of afferent outflow from the gastrointestinal tract. We compared EPs obtained with distension of the distal and proximal esophagus. Responses were recorded with the balloon 5 cm proximal to the lower esophageal sphincter and 3 cm distal to the upper esophageal sphincter. Balloon stimulation resulted in cortical responses recorded by midline scalp electrodes (CZ', PZ, and OZ by the International 10-20 system) in normal volunteers. EP responses consisted of two negative (N1, N2) and one positive (P1) deflections. The proximal esophageal latency of N1 was shorter in all three leads. The latency to P1 was shorter with proximal stimulation in lead CZ' only, and N2 latencies were not different. Amplitudes expressed as the difference between N1 and P1, and P1 and N2 were not different. When two sets of potentials several minutes apart from the proximal position were compared, a decrease in amplitude with the second set of stimulations was noted. Esophageal EP recording is a new technique that may provide information about the integrity and function of the sensory innervation of the esophagus.

Adult↗