Measuring Hemodynamic Changes in the Ophthalmic Artery During Applied Force for Noninvasive Intracranial Pressure Monitoring: Test Results in a Porcine Model

Abstract

Possible traumatic brain injury victims would greatly benefit from a handheld, noninvasive intracranial pressure (ICP) monitoring tool, which a medic could operate in a remote area. Such a device would also benefit the transport of injured soldiers during en route medical care and critical care air transport. This study demonstrates the use of noninvasive blood flow measurements in the eye by ultrasound as a proxy for ICP. ICP was artificially raised in a porcine model and resultant blood flow change in the ophthalmic artery was measured. In addition, the ultrasound transducer itself was used to compress the eye further altering ophthalmic hemodynamics. Blood flow velocities at a range of applied forces and ICP were compared. It was found that 3.25 N of force applied to the cornea was sufficient to produce significant changes in ophthalmic artery blood dynamics regardless of the ICP value. Specifically, the change in resistivity index (RI) and pulsatility index (PI) as force was applied to the cornea correlated with ICP levels. In multiple animal experiments, the magnitude of PI/RI percent change was inversely related to differences in ICP. Force applied to the cornea at baseline ICP resulted in a 15% increase in PI/RI. Results indicate that as ICP increases, the percent change in PI/RI while force is applied decreases. The consistency of data collected indicates that a trend line developed with this data and from similar experiments could be used as a predictive measurement of ICP.

The Effects of Acute Intracranial Pressure Changes on the Episcleral Venous Pressure, Retinal Vein Diameter and Intraocular Pressure in a Pig Model

“…For this exploratory study, we used an established porcine model of acute ICP fluctuations, which was recently developed at our institution, to model non-invasive ophthalmic biomarkers of acute ICP changes. 17 This model was chosen due to prior surgeon experience with lumbar and intracranial CSF access in the species (Sus domesticus) and comparable intra-cranial, intra-orbital and ocular anatomy with humans. 18 In both species, the episcleral veins and retinal veins drain into the cavernous sinus through the superior ophthalmic vein (humans) or the ophthalmic plexus (pigs).…”