Blood flow effects on heart development and a minimally invasive technique for in vivo flow alterations.

Abstract

A series of experiments were conducted on zebrafish (Danio rerio) in order to gain a better understanding of how blood flow and blood flow related forces, such as shear stress, affect vertebrate heart development. Zebrafish were used as a model due to their external fertilization and optical accessibility to the heart and vasculature. The flow field inside the 4.5 day post fertilization (dpf) embryo was analyzed using a combination of manual particle tracking and digital particle image velocimetry (DPIV) software. Our results present the first case of intracardiac microscale DPIV. Additionally, a minimally invasive and reversible technique of delivering and localizing magnetic microspheres inside the vasculature of the embryo was developed. The results of blocked flow induced with this method were compared with previous experiments and controls. The results of the flow field analysis showed the existence of an extremely dynamic flow environment containing jets with a velocity of 5 mm/s and regions of vorticity in a low Reynolds number environment. Calculations of the flow at the 4.5 dpf A-V resulted in wall shear stress levels of 70 dynes/cm2, levels much higher than needed for endothelial cell response. We also showed that injected magnetic microspheres can be delivered and localized within the embryonic vasculature to reversibly block blood flow in the dorsal artery and at the inflow to the heart. Blocked blood flow of 12 hours and longer resulted in lower blood velocity and a less developed heart, exhibiting edema, regurgitance, decreased contractile function, and delayed development. These findings are consistent with previous studies showing that blood flow is a necessary factor for heart development. Furthermore an unexpected result was observed. Exposure to a localized magnetic field eventually caused the absorption of magnetic microspheres into the surrounding tissue. It is theorized that this could be utilized in future studies modeling the effects of reduced cardiac contractility.