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Intravascular pillars and microvascular pruning in the extraembryonic vessels of chick embryos

Microvascular adaptation and remodeling in response to local hemodynamic changes remain largely unknown. We studied the local mechanical forces associated with intravascular pillars and vessel pruning in the extraembryonic circulation of the chick embryos. During the development days 12–16 (n=62), intravascular pillars and blood flow parameters were identified using fluorescent vascular tracers and digital time‐series video reconstructions. To map the mechanical forces associated with the pruning segment, 3‐dimensional finite element models and computational flow simulations of the vascular bifurcation were constructed based on the in vivo‐derived morphometry and the flow measurements. Pruning vessels were associated with convergent flow (74.9±10.3%) and multiple intravascular pillars (91±2.4%). A Reynolds number of 0.03 produced 4 pillars at approximately 20um intervals. In contrast, a Reynolds number of 0.06 produced only 2 pillars at approximately 63um intervals. Our modeling data show that intravascular pillars, constrained by regions of high shear stress, produce progressive flow obstruction in the regressing segment. The combination of wall shear stress and the gradient of shear predicted both the location and direction of developing pillars, as well as periodicity. We suspect our findings will be equally relevant to more comprehensive models of tissue growth and network remodeling.