Blood Flow Values in the Ischemic Brain Tissue as Influenced by Factor m with Loss of Tissue Vivacity

Abstract

Factor m was defined by Kety as the effectiveness of the tissue-capillary diffusion equilibrium. This factor was examined as a possible cause of error in cerebral blood flow (CBF) values in ischemic tissue obtained with a noninvasive instrument using a diffusible tracer. In normal cerebral tissue, we found that m = 1 (establishment of instantaneous equilibrium) and, therefore, that the normal tissue was a well-mixed compartment. However, when the tissue was made ischemic, and the brain cells became “sick” or died, m was found to be < 1. This implies that the use of a diffusible tracer for measuring CBF (i.e., flow values as expressed by CBF = λk/m) becomes erroneous under the ischemic conditions of the brain. We present evidence to suggest that the values of m were closely related to enhancement of gas diffusion in normal tissue, probably owing to a “stirring or mixing” effect occurring under an extraordinarily elevated thermal state in living cells. The values of m are postulated to provide a measure of the living activity of cells or tissues, suggesting a novel interpretation for the changes in diffusion-weighted magnetic resonance imaging that are known to vary with restriction of proton movement in ischemic tissue.