[The cerebral blood flow velocity (CBFV), as measured by transcranial Doppler sonography (TCD) via the transorbital route in the intracranial segment of internal carotid artery (ICA), and the regional cerebral blood (volume) flow (rCBF) in the corresponding cortical areas, as measured by the hydrogen clearance technique, were determined in 8 New Zealand White rabbits undergoing cisterna magna infusion for elevation of the intracranial pressure (ICP). In the lower range of autoregulation, i. e. at perfusion pressures (PP) between 80 and 40 mm of mercury and even below this, the changes in (CBFV) and CBF showed a strong correlation (0,86) under conditions with standard PCO2 (PaCO2)=35+2 mm of mercury). Autoregulation was exhausted at 40 mm of mercury and the cerebrovascular resistance (CVR) was minimal. Below this PP, the CBF and CBV dropped sharply, whereas CVR, gradually increased, indicating that, despite the maximally dilated resistance vessels, the intracranial hypertension causes the vascular resistance to increase, possibly via blocking of the venous outflow. Our results confirmed that non-invasive and easily (even at the bedside) applicable measurements of CBFV changes could substitute the cumbersome and expensive isotope measurements of CBF in intracranial hypertension.]
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