PMC:6194691 / 231958-233114 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/6194691","sourcedb":"PMC","sourceid":"6194691","source_url":"https://www.ncbi.nlm.nih.gov/pmc/6194691","text":"There is, however, an apparent difficulty with accepting the values calculated by Smith and Rapoport. Their analysis of the time course of the concentrations within the cortex started with their Eq. 1,40 dcbrx,tdt=PScplasma-PS′cbrx,tVbr+DVbrd2cbrx,tdx2,which is dimensionally inconsistent. In this equation cbr(x,t) is the concentration of tracer in the parenchyma, units dpm g−1; P is the permeability of the blood–brain barrier, units cm s−1; S is the area of the blood–brain barrier, units cm2 g−1; cplasma is the concentration in plasma, units dpm cm−3; Vbr is the volume of distribution of the tracer substance, units cm3 g−1; D is the diffusion constant of the tracer in the extracellular fluid, units cm2 s−1, x is distance from the ventricular surface, units cm; and t is the time, units s. The units of the first two terms on the right hand side, those which describe blood–brain barrier transport, are dpm s−1 g−1, which is the same as for the left hand side, but the units of the third term, which describes diffusion within the cortex, are dpm s−1 cm−3. Terms with different units cannot be added together, thus this equation cannot be correct.","divisions":[{"label":"label","span":{"begin":201,"end":203}}],"tracks":[]}