Cortical Tissue Pressure Gradients in Early Ischemic Brain Edema

We examined the role of ischemic brain edema, tissue pressure gradients, and regional CBF (rCBF) in adjacent regions of cerebral cortex in cats with middle cerebral artery (MCA) occlusion (MCAO). Tissue pressure, rCBF, and water content were measured from gray matter in the central core and the peripheral margin of the MCA territory over 6 h after MCAO. Ventricular fluid pressure and CSF pressure were recorded. Tissue pressure in the ischemic core, with a flow of ∼5 ml/100 g/min, increased more than that in the periphery where flow was ∼19 ml/100 g/min. Tissue pressure rose progressively to 14.8 ± 1.0 mm Hg in the core over 6 h after MCAO, establishing a significant pressure gradient between that tissue and the lateral ventricle nearby or the subarachnoid space in the middle fossa within the first 3 h. The increase in tissue pressure was linearly related to the amount of edema fluid that developed until the edema reached a severe degree. This study shows that a hydrostatic tissue pressure gradient within ischemic cortex is associated with ischemic brain edema. The magnitude of the gradient that develops is related to the severity of ischemic edema in that tissue.