Pulse propagation by a capacitive mechanism drives embryonic blood flow.

Pulsatile flow is a universal feature of the blood circulatory system in vertebrates and can lead to diseases when abnormal. In the embryo, blood flow forces stimulate vessel remodeling and stem cell proliferation. At these early stages, when vessels lack muscle cells, the heart is valveless and the Reynolds number (Re) is low, few details are available regarding the mechanisms controlling pulses propagation in the developing vascular network. Making use of the recent advances in optical-tweezing flow probing approaches, fast imaging and elastic-network viscous flow modeling, we investigated the blood-flow mechanics in the zebrafish main artery and show how it modifies the heart pumping input to the network. The movement of blood cells in the embryonic artery suggests that elasticity of the network is an essential factor mediating the flow. Based on these observations, we propose a model for embryonic blood flow where arteries act like a capacitor in a way that reduces heart effort. These results demonstrate that biomechanics is key in controlling early flow propagation and argue that intravascular elasticity has a role in determining embryonic vascular function.