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The author discusses pressure gradients and the flow of cerebrospinal fluid and gas during their interchange in encephalography. In vivo observations are substantiated by painstaking in vitro experiments. For example it appears that, when the head is flexed, inflow of gas into the ventricular system is due to the outflow of fluid from the cerebral subarachnoid spaces, which allows expansion of the cerebral hemispheres, thus permitting inflow of gas into the ventricles. Indeed, by properly posturing the head it is possible to fill either the subarachnoid spaces or the ventricles with gas.
When the head is flexed 82 to 90 degrees gas usually enters the fourth ventricle and the aqueduct of Sylvius, which is a useful method of demonstrating lesions affecting these structures. A simple pendulum attached to a celluloid protractor determines the desired angle of flexion. The base line of the protractor is taped along the orbitomeatal base line
Further Studies in Encephalography. JAMA. 1947;134(9):837. doi:10.1001/jama.1947.02880260095031
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