The endothelial glycocalyx is hydrodynamically relevant in arterioles throughout the cardiac cycle

¹ Boston University

^* To whom correspondence should be addressed. E-mail: edamiano{at}bu.edu.

Submitted on January 22, 2008
Revised on February 11, 2008
Accepted on 28 March 2008

	Abstract

The existence of a hydrodynamically relevant endothelial glycocalyx of ~ 0.5 µm in thickness is well established in capillaries and venules in vivo. Since the glycocalyx is likely to have implications for broad areas of vascular physiology and pathophysiology, including endothelial-cell mechanotransduction, vascular permeability, and atherosclerosis, it is necessary to determine the extent to which the glycocalyx is present on arteriolar endothelium. We applied microviscometric analysis to data obtained using micro-particle image velocimetry in cremaster-muscle arterioles of wild-type mice. Due to the puslatile nature of the flow regimes in arterioles, data acquisition was triggered with the electrocardiogram at specific time points in the cardiac cycle. Results show the existence of a hydrodynamically relevant glycocalyx having a mean thickness of 0.38 µm in arterioles ~ 20-70 µm in diameter (n=20), which is ~ 0.13 µm thinner (p=0.03) than that found in previous results in venules having a similar diameter range and under similar hemodynamic conditions. Results from data obtained at multiple time points in the cardiac cycle show that the glycocalyx remains hydrodynamically relevant in arterioles with statistically insignificant changes in mean thickness throughout the cardiac cycle, despite the inherent unsteadiness of the flow regimes in these microvessels. These results provide direct in vivo confirmation of the existence of a hydrodynamically relevant surface glycocalyx that essentially eliminates fluid shear stress on arteriolar endothelium throughout the entire cardiac cycle.

Key Words: atherosclerosis, endothelial cell, hemodynamics, mechanotransduction, microcirculation, pulsatile flow