PMC:6194691 / 74805-76019
Annnotations
{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/6194691","sourcedb":"PMC","sourceid":"6194691","source_url":"https://www.ncbi.nlm.nih.gov/pmc/6194691","text":"It is assumed that this permeability also applies to efflux and to unlabelled water. This permeability is often called the diffusional water permeability, Pd. The major difficulty with this method is that the influx is so great that 70–90% of the tracer arriving in the blood enters the parenchyma in a single pass (see chapter 4 in Bradbury [55] and [283–289]). Thus along much of the length of the microvessels the concentration gradient of the tracer across the microvessel walls driving its influx is much less than the concentration that was added to the blood. The permeability calculated from Eq. 7 using the arterial concentration of the tracer thus seriously underestimates the true water permeability of the blood–brain barrier. Mathematical expressions to correct for this effect have been derived relating the fraction of the tracer extracted from the flow through the blood vessel to the PS product (reviewed in [159]). However, even after correction the calculated values are inaccurate when the extraction fraction is large. Paulson et al. [290] found values about 1/5th of the PS values calculated from osmotic flow as described below and similar values have been determined by others (see [159]).","tracks":[{"project":"MyTest","denotations":[{"id":"30340614-14939058-30706208","span":{"begin":353,"end":356},"obj":"14939058"},{"id":"30340614-4925747-30706208","span":{"begin":353,"end":356},"obj":"4925747"},{"id":"30340614-4419687-30706208","span":{"begin":353,"end":356},"obj":"4419687"},{"id":"30340614-1146566-30706208","span":{"begin":353,"end":356},"obj":"1146566"},{"id":"30340614-3810751-30706208","span":{"begin":353,"end":356},"obj":"3810751"},{"id":"30340614-859448-30706209","span":{"begin":1057,"end":1060},"obj":"859448"}],"namespaces":[{"prefix":"_base","uri":"https://www.uniprot.org/uniprot/testbase"},{"prefix":"UniProtKB","uri":"https://www.uniprot.org/uniprot/"},{"prefix":"uniprot","uri":"https://www.uniprot.org/uniprotkb/"}],"attributes":[{"subj":"30340614-14939058-30706208","pred":"source","obj":"MyTest"},{"subj":"30340614-4925747-30706208","pred":"source","obj":"MyTest"},{"subj":"30340614-4419687-30706208","pred":"source","obj":"MyTest"},{"subj":"30340614-1146566-30706208","pred":"source","obj":"MyTest"},{"subj":"30340614-3810751-30706208","pred":"source","obj":"MyTest"},{"subj":"30340614-859448-30706209","pred":"source","obj":"MyTest"}]},{"project":"2_test","denotations":[{"id":"30340614-14939058-30706208","span":{"begin":353,"end":356},"obj":"14939058"},{"id":"30340614-4925747-30706208","span":{"begin":353,"end":356},"obj":"4925747"},{"id":"30340614-4419687-30706208","span":{"begin":353,"end":356},"obj":"4419687"},{"id":"30340614-1146566-30706208","span":{"begin":353,"end":356},"obj":"1146566"},{"id":"30340614-3810751-30706208","span":{"begin":353,"end":356},"obj":"3810751"},{"id":"30340614-859448-30706209","span":{"begin":1057,"end":1060},"obj":"859448"}],"attributes":[{"subj":"30340614-14939058-30706208","pred":"source","obj":"2_test"},{"subj":"30340614-4925747-30706208","pred":"source","obj":"2_test"},{"subj":"30340614-4419687-30706208","pred":"source","obj":"2_test"},{"subj":"30340614-1146566-30706208","pred":"source","obj":"2_test"},{"subj":"30340614-3810751-30706208","pred":"source","obj":"2_test"},{"subj":"30340614-859448-30706209","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"MyTest","color":"#93c6ec","default":true},{"id":"2_test","color":"#e0ec93"}]}]}}