AUTOREGULATION OF CEREBRAL BLOOD FLOW IN THE AWAKE NEWBORN PUPPY

Abstract

Hypertension induced surges in blood flow to the subependymal germinal matrix (GM) may be important in the pathogenesis of neonatal IVH. We measured regional cerebral blood flow (rCBF) to 30 brain regions in 17 awake newborn puppies with quantitative autoradiography and ¹⁴C-iodoantipyrine as tracer. Blood flow was studied during moderate hypotension (MAP 35-50 mmHg) in 4, during normotension (50-70 mmHg) in 6, and during phenylephrine induced hypertension (75-105 mmHg) in 7. An autoregulatory plateau was seen for all brain regions over the range 35-70 mmHg. In gray matter, increases in MAP above 75 mmHg significantly increased rCBF; hypertensive incremental CBF (ICBF) was greater in brainstem nuclei than in cerebral cortex (eg, ICBF .142 ml/min/g/mmHg for oculomotor nucleus, .019-.069 ml/min/g/ mmHg for parietal cortex). For white matter, ICBF remained low (.001-.006 ml/min/g/ mmHg) even when MAP exceeded 75 mmHg. GM blood flow did not react uniformly to hypertension. Hypertensive ICBF to posterior GM was low and similar to white matter while ICBF to rostral, densely cellular GM was higher (.014 ml/min/g/mmHg) and similar to some cortical regions. From our data we have concluded the following: 1) autoregulation of rCBF is intact for all brain regions including GM for physiologic MAP; 2) at MAP above the autoregulatory plateau, rostral GM blood flow increases more than blood flow to adjacent white matter. These increases in GM blood flow during hypertension may contribute to the genesis of IVH. Differences in hypertensive ICBF between GM and white matter may partially explain the selective vulnerability of the GM for hemorrhage.

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