Harris A, Arend O, Wolf S, Cantor L B, Martin B J
Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, USA.
Acta Ophthalmol Scand. 1995 Oct;73(5):421-4. doi: 10.1111/j.1600-0420.1995.tb00301.x.
Blood flow to the brain is extremely sensitive to changes in PCO2. While animal studies show a similar potent PCO2 dependence in retinal and choroidal vessels, the PCO2-retinal blood flow relationship has never been adequately studied in humans.
Video scanning laser ophthalmoscopy after fluorescein angiography was used to analyze retinal arterial and capillary blood velocity under conditions of mild hypercapnia and hypocapnia. Control conditions (end-tidal PCO2 = 38.3 +/- 0.4 mmHg) were contrasted with hyperventilation-induced hypocapnia (PCO2 = 34.0 +/- 0.4 mmHg) and hypercapnia (PCO2 = 42.3 +/- 0.5 mmHg) created by PCO2 addition to inspired gas.
Both larger vessel and macular capillary blood velocity was dependent upon PCO2: arteriovenous passage time fell as PCO2 rose, and both mean arterial dye velocity and capillary blood velocity rose as PCO2 rose (all p < 0.05). These changes in flow velocity occurred despite unchanged heart rate, arterial systolic and diastolic blood pressure, intraocular pressure, and calculated ocular perfusion pressure. Contrast sensitivity was also unchanged by PCO2 variation.
The human retinal circulation, like the whole cerebral circulation, may be strongly dependent upon PCO2 in a manner that is unrelated to perfusion pressure and apparently outside strict autoregulatory controls.
脑血流量对PCO2的变化极为敏感。虽然动物研究表明视网膜和脉络膜血管对PCO2也有类似的强烈依赖性，但PCO2与视网膜血流量之间的关系在人类中从未得到充分研究。
在荧光素血管造影后，使用视频扫描激光检眼镜分析轻度高碳酸血症和低碳酸血症条件下的视网膜动脉和毛细血管血流速度。将对照条件（呼气末PCO2 = 38.3±0.4 mmHg）与通过向吸入气体中添加PCO2产生的过度通气诱导的低碳酸血症（PCO2 = 34.0±0.4 mmHg）和高碳酸血症（PCO2 = 42.3±0.5 mmHg）进行对比。
较大血管和黄斑毛细血管的血流速度均取决于PCO2：随着PCO2升高，动静脉通过时间缩短，平均动脉染料流速和毛细血管血流速度均随PCO2升高而增加（所有p < 0.05）。尽管心率、动脉收缩压和舒张压、眼压以及计算出的眼灌注压未变，但流速仍发生了这些变化。PCO2变化对对比敏感度也没有影响。
人类视网膜循环与整个脑循环一样，可能强烈依赖于PCO2，其方式与灌注压无关，且显然不受严格的自身调节控制。
