Effect of hypoxemia and hypovolemia on retinal and choroidal blood flow in the newborn piglet.

The effect of hypoxemia and/or hypovolemia on ocular blood flow was studied in paralyzed and mechanically ventilated newborn piglets with the isotope-labelled microsphere method. Twenty-six piglets were studied in four different groups. One group of piglets (n = 6) was made hypoxemic by breathing 10% O2, a second group (n = 7) and a third group (n = 7) were studied during hypoxemia (10% O2), followed by hypovolemia (bleeding 20 and 30% of estimated blood volume, respectively). A fourth group of piglets (n = 6) was made hypovolemic by bleeding 20% of estimated blood volume. Hypoxemia resulted in a 2- to 3-fold increase in retinal blood flow (RBF), while hypovolemia did not change RBF, not even when preceded by a period of hypoxemia. In the case of choroidal blood flow (ChBF), the increase caused by hypoxemia was only 10-40%. Although ChBF decreased significantly during hypovolemia, no significant correlation between mean arterial blood pressure and ChBF was found. The results indicate that autoregulation is normally seen in RBF, but probably not in ChBF. However, during hypoxemia autoregulation was found neither in RBF nor in ChBF.