1396 REGIONAL CEREBRAL BLOOD FLOW (CBF) RESPONSE TO APNEA IN NEWBORN (NB) PIGLETS

Abstract

Previous studies have shown that sustained steady-state hypoxemia results in increased CBF with greatest increases to brainstem and subcortical structures. The present study investigates acute regional CBF response to single and repeated short (130 - 180 sec) apneas in 5 NB piglets. After catheterization and tracheostomy, piglets were paralyzed and mechanically ventilated (PO₂=60-70, pH=7.35-7.45, PCO₂=30-35) with 30% N₂O. Following baseline measurements of blood gases, pH, Hct, BP, HR, and CBF by microspheres, apnea to the point of bradycardia (HR<80) was induced by disconnecting the ventilator, and repeated for a total of 7 apneas. CBF was measured during the first apnea (PO₂=16 ± 13 torr, pH = 7.34 ± .06, PCO₂ = 42 ± 5), recovery from first apnea (Rec 1), and ½ hr after the 7th apnea (Rec 2). During apnea, rapid regional CBF redistribution occurs, with decreased flow to the cerebrum 56 ± 4 ml/min/100g to 43 ± 7, -23%, caudate 76 ± 14 to 73±22, -10%, and choroid plexus 148 ± 25 to 86 ± 22, -<t3%, although total brain flow increased 66 ± 8 to 84 ± 15, +28%. Flow increased significantly (70 - 200%) to brainstem structures (midbrain 64 ± 6 to 108 ± 17, pons 90 ± 26 to 183 ± 61, medulla 59 ± 4 to 174 ± 28) with moderate increases (28 - 40%) to subcortical structures (thalamus 64 ± 7 to 88 ± 11, hippocampus 38 ± 4 to 51 ± 11, cerebellum 52 ± 3 to 67 ± 8). During Rec 1 and Rec 2, CBF remained elevated from baseline, 58% and 37%, respectively; the regional flow returned, however, to a more uniform distribution pattern. The nonhomogeneous regional CBF during apnea suggests differences in regional metabolism, response time, or vascular sensitivity to hypoxemia in the newborn brain.

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