CEREBRAL BLOOD-FLOW AUTOREGULATION AFTER MODERATE HYPOXEMIA IN THE NEWBORN PIGLET

The isotope-labelled microsphere method was used to study blood flow a utoregulation in the brainstem (BS), cerebellum (CBL), cerebrum (CBR) and choroid plexus (ChP1) in 21 newborn piglets exposed to hypoxemia a nd/or hypovolemia. One group of piglets (n = 7) was made hypoxemic by breathing 10% O-2 for 10 min, a second group (n = 8) was studied durin g hypoxemia (10% O-2, 10 min), followed by hypovolemia (bleeding 20% o f estimated blood volume). A third group of piglets (n = 6) was made h ypovolemic by bleeding 20%. Hypoxemia significantly impaired the autor egulatory capacity in CBL and CBR resulting in a pressure-passive flow pattern. Hypovolemia alone did not produce any significant cerebral v ascular response in BS, CBL and CBR, not even when hypovolemia was pre ceded by hypoxemia, indicating a rapid restoration of the autoregulato ry capacity of the cerebral vasculature after hypoxemia of moderate du ration. The hypotension seen both during hypoxemia and hypovolemia was gradually compensated for and normalized within 60 min. However, anim als exposed to both hypoxemia and hypovolemia were still hypotensive 6 0 min after the hypoxemic insult. Cardiac output (CO) was not affected by hypoxemia, but was consistently reduced in hypovolemia. We therefo re speculate that in the newborn a reduced CO might be a more specific parameter for hypovolemia than a low blood pressure.