Kang Derwent J, Linsenmeier R A
Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208-3107, USA.
Invest Ophthalmol Vis Sci. 2000 Oct;41(11):3634-42.
Slow components of the electroretinogram (ERG) are sensitive to even mild hypoxemia (60 < P(a)O(2) < 100 mm Hg) in the cat eye. However, the electrical responses of the inner retina remain unchanged until P(a)O(2) is below 40 mm Hg. In this study, the effects of hypoxemia on photoreceptors, on which both slow ERG components and inner retinal activity depend, were examined by recording the a-wave of the ERG.
The ERG of dark-adapted, anesthetized cats was recorded between an Ag-AgCl electrode in the vitreous humor and a reference electrode near the eye. Responses to bright flashes of diffuse white light were recorded at 3-minute intervals during hypoxemic episodes lasting 15 minutes to 2 hours.
The cat a-wave was well described by the Lamb and Pugh a-wave model during normoxia and hypoxemia. During mild hypoxemia (P(a)O(2) of 50-60 mm Hg), small changes in a-wave amplitude were detected but did not become greater during severe hypoxemia. The mean decrease in the a-wave amplitude during severe hypoxemia (P(a)O(2) of 20-30 mm Hg) was 8.9% from the mean amplitude during air breathing. The effects of hypoxemia were more severe on the b-wave amplitude. The mean decrease in the b-wave was 35% at P(a)O(2) of 20-30 mm Hg.
The a-wave is more resistant to severe hypoxemia than the b-wave. This implies that photoreceptor transduction works almost normally during hypoxemia and that failure of inner retinal PO(2) regulation causes the decrease in the b-wave. Previously observed changes in the amplitudes of slow ERG components during hypoxemia may result from changes in the ionic environment, rather than a failure of photoreceptor energy metabolism.
视网膜电图（ERG）的慢成分对猫眼即使是轻度低氧血症（60＜动脉血氧分压[P(a)O(2)]＜100mmHg）也很敏感。然而，直到P(a)O(2)低于40mmHg时，视网膜内层的电反应才会发生变化。在本研究中，通过记录ERG的a波，研究了低氧血症对光感受器的影响，ERG的慢成分和视网膜内层活动均依赖于光感受器。
在玻璃体中的银-氯化银电极与眼附近的参考电极之间记录暗适应、麻醉猫的ERG。在持续15分钟至2小时的低氧血症发作期间，每隔3分钟记录对漫射白光强光闪烁的反应。
在常氧和低氧血症期间，猫的a波可用Lamb和Pugh a波模型很好地描述。在轻度低氧血症（P(a)O(2)为50-60mmHg）期间，检测到a波振幅有小的变化，但在重度低氧血症期间并未变得更大。重度低氧血症（P(a)O(2)为20-30mmHg）期间a波振幅的平均降低幅度相对于呼吸空气时的平均振幅为8.9%。低氧血症对b波振幅的影响更严重。在P(a)O(2)为20-30mmHg时，b波的平均降低幅度为35%。
a波比b波对重度低氧血症更具抵抗力。这意味着在低氧血症期间光感受器转导几乎正常工作，并且视网膜内层PO(2)调节功能的衰竭导致b波降低。先前观察到的低氧血症期间ERG慢成分振幅的变化可能是离子环境变化所致，而非光感受器能量代谢功能的衰竭。
