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 st udied in paralyzed and mechanically ventilated newborn piglets with th e isotope-labelled microsphere method. Twenty-six piglets were studied in four different groups. One group of piglets (n = 6) was made hypox emic by breathing 10% 02, a second group (n = 7) and a third group (n = 7) were studied during hypoxemia (10% 02), 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 esti mated blood volume. Hypoxemia resulted in a 2- to 3-fold increase in r etinal blood flow (RBF), while hypovolemia did not change RBF, not eve n when preceded by a period of hypoxemia. In the case of choroidal blo od flow (ChBF), the increase caused by hypoxemia was only 10-40%. Alth ough ChBF decreased significantly during hypovolemia, no significant c orrelation between mean arterial blood pressure and ChBF was found. Th e results indicate that autoregulation is normally seen in RBF, but pr obably not in ChBF. However, during hypoxemia autoregulation was found neither in RBF nor in ChBF.