Determination of microvascular flow pattern formation in vivo

Abstract

Blood flow in microvessels differs significantly from that of red blood cells (RBC) flowing through long, straight glass tubes in vitro. The in vivo situation is characterized by the presence of plasma favoring aggregation, by the irregular geometry of vessel segments, and by frequent branching points. Here, a method is presented to characterize flow patterns in microvascular blood flow during intravital microscopy based on Fourier analysis of recorded light intensity patterns. The interpretation of the resulting power spectra in terms of pattern size distribution was validated by model experiments employing artificial textures and by reverse transformation of idealized spectra. The determined size of RBC flow patterns in microvessels ranged from approximately 8 microm in capillaries to approximately 14 microm in vessels of >30 microm. With increasing shear rate above approximately 100 s(-1) pattern size increased, possibly reflecting formation of short-lived flow clusters. Below approximately 100 s(-1) an increase of pattern size with decreasing shear rate was found in experiments using local occlusion and treatment with high-molecular-weight dextran, suggesting the formation of aggregates. The dynamic process of generation and destruction of RBC flow patterns could well contribute to flow resistance in vivo in peripheral vascular beds.

Effects of iodinated contrast media on common carotid and brachial artery blood flow and wall shear stress

“…Similar findings have been previously reported by others [7,8,28,29]. On the basis of the formula used in our study, the hemodilution induces a reduction in WSS that in turn causes, as demonstrated by others, a modification in erythrocyte aggregation and aggregate size [30,31]. It is known that physiologically, in small vessels, erythrocytes tend to aggregate to form rouleaux reducing peripheral resistances.…”

Hyperaggregating Effect of Hydroxyethyl Starch Components and University of Wisconsin Solution on Human Red Blood Cells

“…Some authors have advocated a more physiologic method in which the UW solution is flushed under pressure (100 mm Hg), similar to the mean arterial blood pressure with the advantage of perfusing the small intrahepatic vessels. Measurement of the microvascular blood flow patterns in physiologic conditions using intravital microscopy shows that in arterioles and venules with a diameter of 24.7 Ϯ 9.1 m, the recorded shear rate has a mean value of 201Ϯ163 sec Ϫ1 (21). The minimal value of the shear rate that prevented UWinduced aggregation in the authors' experiments was 175Ϯ29 sec Ϫ1 .…”

“…RBC aggregability and deformability were investigated in vitro with a laser-assisted optical rotation cell analyzer (LORCA R&R Mechatronics, Hoorn, The Netherlands) (20,21). This instrument, based on the ektacytometric principle, is equipped with a video camera for detection of the laser diffraction pattern, a thermostation unit, and an ellipse-fit computer program calculating the Elongation Index and Aggregation Index (AI).…”

Aggregate formation of erythrocytes in postcapillary venules

“…It is possible that these aggregates represent short-lived red cell clusters brought in close contact solely by hemodynamic forces as suggested by Osterloh et al (29). They reported a mean particle size considerably greater than that of red cells at high shear rates in pre-and postcapillary vessels (ϳ25 m) using a spatial Fourier analysis of light intensity patterns.…”

“…Not surprisingly, these aggregates formed further downstream, between 40 and 55 m from the entrance to the postcapillary venule. Osterloh and coworkers (29) found that the pattern size of particles in preand postcapillary vessels increased at pseudoshear rates both higher and lower than ϳ150 s after infusion of dextran 250 (800 mg/kg body wt). The presence of aggregation at high pseudoshear rates in their study and ours may be explained not only by the hemodynamic forces mentioned above but also by the macromolecules of dextran once the hemodynamic forces bring red blood cells into close contact.…”