Tissue Oxygen Demand in Regulation of the Behavior of the Cells in the Vasculature

Abstract

The control of arteriolar diameters in microvasculature has been in the focus of studies on mechanisms matching oxygen demand and supply at the tissue level. Functionally, important vascular elements include EC, VSMC, and RBC. Integration of these different cell types into functional units aimed at matching tissue oxygen supply with tissue oxygen demand is only achieved when all these cells can respond to the signals of tissue oxygen demand. Many vasoactive agents that serve as signals of tissue oxygen demand have their receptors on all these types of cells (VSMC, EC, and RBC) implying that there can be a coordinated regulation of their behavior by the tissue oxygen demand. Such functions of RBC as oxygen carrying by Hb, rheology, and release of vasoactive agents are considered. Several common extra- and intracellular signaling pathways that link tissue oxygen demand with control of VSMC contractility, EC permeability, and RBC functioning are discussed.

Basic Concepts of Hemorheology in Microvascular Hemodynamics

“…2). 3 In pathologic states with reduced erythrocyte deformability (eg, sickle cell disease), erythrocyte sequestering takes place at the capillary entrance, further increasing the resistance to microvascular blood flow. 11,15 Erythrocyte Aggregation When suspended in aqueous solutions containing large plasma proteins such as fibrinogen, erythrocytes are able to aggregate to form 2-and 3-dimensional structures.…”

“…Deformation, a critical concept in the understanding of fluid dynamics, is the relative displacement of material (eg, erythrocytes) by the use of force (eg, vessel diameter) such that the deformation is proportional to the applied force; shape recovery occurs when the force is removed with a time constraint of 0.1 second. 2,3 The force or stress applied per unit area is considered when discussing the degree of deformation, and involves (1) shear stress when the force is acting parallel to the surface and (2) normal stress when the force is acting perpendicular to the surface, also known as the pressure in a fluid. 2 Shear rate is the degree of deformation.…”

Mechanical, hormonal and metabolic influences on blood vessels, blood flow and bone

“…Metabolic vasodilation is necessary for delivering blood to tissues such as skeletal muscle and the heart (Rowell 1993; Barvitenko et al 2013), particularly in the face of increased metabolism. In reference to dynamically active skeletal muscle, many factors released into the interstitial space produce vasomotor activity of the nearby vasculature.…”

Microcirculatory Oxygen Transport and Utilization

“…30 This distinctive microvascular flow behavior maximizes the surface area available for gas exchange 1 ; RBC deformability is the most important rheological factor affecting blood flow. 31 Worthy of consideration is the tendency for RBCs to clump together or aggregate. Aggregation increases flow resistance and viscosity, and is facilitated in low-shear conditions, especially those with increased levels of circulating fibrinogen, such as in sepsis.…”