Editing Rheology (section)

=== Physiology ===

Physiology includes the study of many bodily fluids that have complex structure and composition, and thus exhibit a wide range of viscoelastic flow characteristics.  In particular there is a specialist study of blood flow called [[hemorheology]]. This is the study of flow properties of blood and its elements ([[Blood plasma|plasma]] and formed elements, including [[red blood cell]]s, [[white blood cell]]s and [[platelet]]s). [[Blood viscosity]] is determined by plasma viscosity, [[hematocrit]] (volume fraction of red blood cell, which constitute 99.9% of the cellular elements) and mechanical behaviour of red blood cells. Therefore, red blood cell mechanics is the major determinant of flow properties of blood.(The ocular [[Vitreous humor]] is subject to rheologic observations, particularly during studies of age-related vitreous liquefaction, or [[synaeresis]].)<ref>{{cite journal |doi= 10.1055/s-2003-44551 |author= Baskurt OK, Meiselman HJ |title= Blood rheology and hemodynamics |journal= Seminars in Thrombosis and Hemostasis |volume=29 |issue= 5 |pages=435–450 |year=2003 |pmid= 14631543 |last2= Meiselman |s2cid= 17873138 }}</ref>

The leading characteristic for hemorheology has been [[shear thinning]] in steady shear flow. Other non-Newtonian rheological characteristics that blood can demonstrate includes [[pseudoplasticity]], [[viscoelasticity]], and [[thixotropy]].<ref name="Beris-2021">{{Cite journal |last1=Beris |first1=Antony N. |last2=Horner |first2=Jeffrey S. |last3=Jariwala |first3=Soham |last4=Armstrong |first4=Matthew J. |last5=Wagner |first5=Norman J. |date=2021 |title=Recent advances in blood rheology: a review |journal=Soft Matter |volume=17 |issue=47 |pages=10591–10613 |doi=10.1039/D1SM01212F |pmid=34787149 |arxiv=2109.05088 |bibcode=2021SMat...1710591B |s2cid=237492003 }}</ref>

==== Red blood cell aggregation ====
There are two current major hypotheses to explain blood flow predictions and [[shear thinning]] responses. The two models also attempt to demonstrate the drive for reversible red blood cell aggregation, although the mechanism is still being debated. There is a direct effect of red blood cell aggregation on blood viscosity and circulation.<ref name="Lee-2017">{{Cite journal |last1=Lee |first1=Kisung |last2=Wagner |first2=Christian |last3=Priezzhev |first3=Alexander V. |date=2017 |title=Assessment of the "cross-bridge"-induced interaction of red blood cells by optical trapping combined with microfluidics |journal=Journal of Biomedical Optics |volume=22 |issue=9 |pages=091516 |doi=10.1117/1.JBO.22.9.091516 |pmid=28636066 |bibcode=2017JBO....22i1516L |s2cid=27534435 |doi-access=free }}</ref> The foundation of [[hemorheology]] can also provide information for modeling of other biofluids.<ref name="Beris-2021" /> The bridging or "cross-bridging" hypothesis suggests that macromolecules physically crosslink adjacent red blood cells into rouleaux structures. This occurs through adsorption of macromolecules onto the red blood cell surfaces.<ref name="Beris-2021" /><ref name="Lee-2017" /> The depletion layer hypothesis suggests the opposite mechanism. The surfaces of the red blood cells are bound together by an osmotic pressure gradient that is created by depletion layers overlapping.<ref name="Beris-2021" /> The effect of rouleaux aggregation tendency can be explained by [[hematocrit]] and fibrinogen concentration in whole blood rheology.<ref name="Beris-2021" /> Some techniques researchers use are optical trapping and microfluidics to measure cell interaction in vitro.<ref name="Lee-2017" />

==== Disease and diagnostics ====
Changes to viscosity has been shown to be linked with diseases like hyperviscosity, hypertension, sickle cell anemia, and diabetes.<ref name="Beris-2021" /> [[Hemorheological]] measurements and genomic testing technologies act as preventative measures and diagnostic tools.<ref name="Beris-2021" /><ref>{{Cite journal |last1=Hurst |first1=Anna C. E. |last2=Robin |first2=Nathaniel H. |date=2020 |title=Dysmorphology in the Era of Genomic Diagnosis |journal=Journal of Personalized Medicine |volume=10 |issue=1 |pages=18 |doi=10.3390/jpm10010018 |pmc=7151624 |pmid=32192103 |doi-access=free }}</ref>

[[Hemorheology]] has also been correlated with aging effects, especially with impaired blood fluidity, and studies have shown that physical activity may improve the thickening of blood rheology.<ref>{{Cite journal |last1=Simmonds |first1=Michael J. |last2=Meiselman |first2=Herbert J. |last3=Baskurt |first3=Oguz K. |date=2013 |title=Blood rheology and aging |journal=Journal of Geriatric Cardiology |volume=10 |issue=3 |pages=291–301 |doi=10.3969/j.issn.1671-5411.2013.03.010 |doi-broken-date=1 November 2024 |pmid=24133519 |pmc=3796705 }}</ref>