Microvascular blood flow resistance: role of endothelial surface layer

Abstract

Observations of blood flow in microvascular networks have shown that the resistance to blood flow is about twice that expected from studies using narrow glass tubes. The goal of the present study was to test the hypothesis that a macromolecular layer (glycocalyx) lining the endothelial surface contributes to blood flow resistance. Changes in flow resistance in microvascular networks of the rat mesentery were observed with microinfusion of enzymes targeted at oligosaccharide side chains in the glycocalyx. Infusion of heparinase resulted in a sustained decrease in estimated flow resistance of 14–21%, hydrodynamically equivalent to a uniform increase of vessel diameter by ∼1 μm. Infusion of neuraminidase led to accumulation of platelets on the endothelium and doubled flow resistance. Additional experiments in untreated vascular networks in which microvascular blood flow was reduced by partial microocclusion of the feeding arteriole showed a substantial increase of flow resistance at low flow rates (average capillary flow velocities < 100 diameters/s). These observations indicate that the glycocalyx has significant hemodynamic relevance that may increase at low flow rates, possibly because of a shear-dependent variation in glycocalyx thickness.

Hyaluronidase treatment of coronary glycocalyx increases reactive hyperemia but not adenosine hyperemia in dog hearts

“…increase in conductance likely reflects an increase in coronary vascular volume available for blood flow. Pries et al (1997) calculated that effective vessel diameter available for red blood cell and plasma motion had increased by at least 0.35-0.55 m after a single ϳ10 min infusion of heparinase in the rat mesentery bed. Indeed, a glycocalyx with these dimensions is typically reported in capillaries of cremaster tissue (6,21,30,31), and has been suggested to be present in myocardial capillaries as well (26).…”

“…However, it was shown that adenosine superfusion impaired glycocalyx exclusion properties (21). Because an intact glycocalyx strongly reduces the volume available for flow of plasma and red blood cells in capillaries (3,22,30), an impaired glycocalyx exclusion during adenosine is consistent with an increase in functionally perfused capillary volume, and as a result, elevated capillary tube hematocrit (12).The aim of the present study was to determine to which extent the glycocalyx limits coronary hyperemia obtained with adenosine compared with hyperemia obtained by an ischemic stimulus [reactive hyperemia (18)]. In anesthetized dogs, coronary pressure and flow were measured in the left circumflex artery, and reactive hyperemia was compared with the hyperemia induced by intracoronary injection of adenosine.…”

“…However, it was shown that adenosine superfusion impaired glycocalyx exclusion properties (21). Because an intact glycocalyx strongly reduces the volume available for flow of plasma and red blood cells in capillaries (3,22,30), an impaired glycocalyx exclusion during adenosine is consistent with an increase in functionally perfused capillary volume, and as a result, elevated capillary tube hematocrit (12).…”

Study on the Sliding Friction of Endothelial Cells Cultured on Hydrogel and the Role of Glycocalyx on Friction Reduction

“…It was demonstrated that heparinase treatment reduced the fluorescence intensity of fluorescence-labeled wheat germ agglutinin by 27-51% [41] and the fluorescence intensity associated with the heparan sulfate antibody by 45.9% [40]. Furthermore, the thickness and negative charge of the glycocalyx were reduced by heparinase disruption [44].…”

Theoretical and experimental study of the porous film using quartz crystal microbalance

“…This predicted value is larger than the wall shear stress exerted by the blood flow with a typical value of 2 Pa in a 6 lm capillary and smaller than the deforming stress of red blood cells with a typical value of 6 Pa. 71 This explains why the ESL can maintain its shape in blood flow but is crushed by motionless red blood cells in capillaries. 72 If we consider the film rigid, we can use the Sauerbrey equation. Using different resonant frequencies, the film thickness has different theoretical values: H 1 ¼ 118:0 nm, H 3 ¼ 98:3 nm, H 5 ¼ 88:5 nm, and H 7 ¼ 84:3 nm, where the subscripts denote the resonant order.…”