THE EFFECT OF RAISED INSPIRED CARBON-DIOXIDE ON DEVELOPING RAT RETINAL VASCULATURE EXPOSED TO ELEVATED OXYGEN

Hyperoxia is a risk factor for retinopathy of prematurity (ROP), a bli nding disease in infants. However, ROP develops in human infants witho ut raised arterial oxygen levels, such as in cyanotic congenital heart disease. In these infants raised pCO(2) may be a risk factor. We inve stigated the effect of inspired CO2 on oxygen induced retinopathy in t he rat. 56 newborn Sprague-Dawley rats were exposed to high cyclical O -2 for seven days. In a control group, 27 rats were exposed to negligi ble CO2 by the use of soda lime. In the high CO2 group, 29 rats were e xposed to elevated CO2 by omitting soda lime from their chambers. Rats in both groups had a recovery period of three days in room air follow ing cyclical O-2 exposure. On the eleventh day all rats were sacrifice d after intracardiac injections of fluorescein under deep anesthesia a nd the retinae were dissected and nat mounted for fluorescent microsco py. The ratio of vascularized:total retinal area was calculated using computer assisted image analysis. In the high CO2 group 62% +/- 7% SD of the retina was vascularized vs. 81% +/- 7% in low CO2 group (p<0.00 1). Elevated inspired CO2 results in pronounced retardation of retinal vascular development in neonatal rats exposed to fluctuating raised o xygen.