HYPOXIA REDUCES THE EFFECT OF PHOTORECEPTOR BLEACHING IN HUMANS AND IN RATS

• Main Authors: Yun-Bin Lin, 林雲彬
• Other Authors: Yin Chang
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/10435898153835840838

博士 === 國立陽明大學 === 醫學工程研究所 === 100 === Hypoxia and light illumination can both decrease oxygen consumption in the photoreceptor layers. The purpose of the present study was to investigate whether the mutual effects of hypoxia and intense illumination to the photoreceptors are additive. The a-wave of flash electroretnogram (fERG) was recorded to indirectly measure the photoreceptors function under given conditions. Human subjects and rats are investigated for the bleaching effect in this dissertation. Six normal healthy human subjects, mean age 34.0  3.8 years, all of whom had high-altitude (> 3000 m) mountain hiking experience, were recruited for the study. Flash a-wave electroretinography was examined under four conditions: (a) normal (D/N); (b) systemic hypoxia induced by inhaling a mixture of O2 and N2 gases, which caused oxyhemoglobin saturation (SaO2)  80% (D/H); (c) intense light illumination , which resulted in photoreceptor bleaching (B/N); and (d) a combination of conditions b and c (B/H). Thirty light stimuli, each with a 20 ms ON and 1,980 ms OFF cycle, were given and ERG performed to probe the photoreceptor function. The results showed that a-wave at the various conditions did not respond to all stimuli. The average a-wave amplitudes were 91.446.5, 22.842.5, 15.528.9, and 35.241.1 V for D/N, D/H, B/N, and B/H, respectively. Nonparametric Friedman test for a-wave amplitude indicated that significant differences occurred in D/N-D/H, D/N-B/N, D/N-B/H, D/H-B/H and B/N-B/H (all p values were <0.001, but D/H-B/N was 0.264). Thus systemic hypoxia or strong illumination to the retina can cause an absence of the ERG a-wave or change its response, although individual differences were observed. In this study, systemic hypoxia appeared to reduce photoreceptor bleaching, an interesting finding in itself. The mechanisms underlying the disappearance of the ERG a-wave following hypoxia or intense illumination to the photoreceptors seem to differ. Normal and hypoxia adaptive rats were investigated to perform the same D/N, D/H, B/N and B/H test condition like human subjects. Different amplitude were observed at b-wave and c-wave amplitude between normal rats and hypoxia adaptive rats.