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

Abstract

The cardiovascular effects resulting from an acute elevation in cerebrospinal fluid (CSF) pres-sure to levels higher than arterial blood pressure were fully described by Cushing and are well known (1, 2). However, the extent to which in-tracranial blood flow is altered by moderate in-creases in CSF pressure has not been fully clari-fied. Using a plethysmographic method of meas-uring cerebral blood flow in two subjects, Ferris found a decrease in flow following acute eleva-tion of the CSF pressure above 350 mm H20 (3). Kety, Shenkin, and Schmidt measured cere-bral blood flow (nitrous oxide technique) in 13 patients and found that flow was uniformly de-pressed in patients having a CSF pressure greater than 450 mm H20 (4). On the other hand, Green, Rapela, and Conrad recently stated, "Artificially induced changes of cerebrospinal fluid pressure have little effect on flow unless the pressure is elevated above arterial pressure " (5). Similarly, Williams and Lennox found that moderately ele-vated levels of CSF pressure had no significant effect on cerebral blood flow (6). Since the results of the foregoing investigations are conflicting, a quantitative evaluation of the relation between the level of CSF pressure and cerebral blood flow should be of interest. The pur-pose of the present study was to measure the effects of incremental increases in CSF pressure on the human cerebral circulation. * Submitted for publication February 10, 1965; ac-