Observations on Continuous Vascular Pulsative Phenomena in the Cerebral Cortex of Experimental Animals with Special Reference to the Effects of Closed vs. Opened Calvarium

Abstract

Preliminary observations have been made on continuous recordings of change in optical density of the cerebral cortex and of the ipsilateral ear with vascular pulsation in anesthetized cats and in fully conscious monkeys with chronic implantation of transducers. The technique used employs fiber optic light guides implanted onto the surface of the cortex through openings in the skull and meninges. The calvarium is reclosed with dental cement. Light guides are attached to the ipsilateral ear by means of teflon receptacles sewn to opposing surfaces. Change in light intensity with change in optical density of tissue is converted by a photocell to a voltage for polygraphic recording. The electrocardiogram is recorded simultaneously. The data suggests that where changes in intracranial pressure occur within the range of normal physiologic variation, mechanisms regulating cerebrovascular distensibility provide remarkable stability. In this, integrity of the calvarium may have an important though limited role, since by allowing for establishment of intracranial pressures which can vary widely above and below atmospheric pressure, integrity of the calvarium may allow for finer adjustment in vascular transmural pressure as this affects vascular distensibility. At atmospheric pressure, decrease in propagation time and in vascular distensibility appears to have a lower limit. At this lower limit, introduction of a skull defect of significant size causes no further decrease in propagation time. It is suggested that under these circumstances other mechanisms—metabolic, mechanical, or both—become engaged even more prominently in preserving the stability of the system.