Effect of Acute Increase in Intracranial Pressure on Blood Flow in the Internal Carotid Artery of Man*

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Abstract
With an electromagnetic flowmeter and a pressure transducer, internal carotid arterial blood flow and pressure were measured continously in 13 awake patients during incremental increases in cerebrospinal fluid (CSF) pressure to a level slightly below each patient''s diastolic blood pressure. The control value of mean flow for the group was 201 cm3/sec (SE [plus or minus] 16) obtained at a cerebrospinal fluid pressure of 190 mm H2O (SE [plus or minus] 13). Flow became significantly decreased at a CSF pressure of 380 mm H2O (SE [plus or minus] 11), and at a CSF pressure of 920 mm H2O (SE [plus or minus] 46) mean flow averaged 25% less than the control value. No change was observed in the blood pressure, heart rate, electrocardiogram, or electroencephalogram. In 4 patients, slight autoregulation of flow was found at the highest level of CSF pressure. In 3 additional patients angiographic studies demonstrated that the cerebral veins lying within the subarachnoid space are not collapsed at a CSF pressure of 1000 mm H2O.