Blood shear stress and flow velocity : challenges for laser coagulation and hemostasis of large vessels

Photo-coagulation of blood vessels offers stark advantages to current radiofrequency mediated devices, given the high specificity of blood absorption wavelengths (like 532nm, 1.064 μm). Existing literature has documented coagulation in treatment of pediatric vascular diseases like port-wine stains for microvascular hemostasis. Although laser treatments have been successful in smaller diameter blood vessels, treatment of larger sized vessels are less effective in achieving hemostasis. This report investigates the hypothesis that a primary limitation in coagulation of larger sized vessels comes from shear stress gradients with higher flow velocities along with temperature dependent viscosity changes. Laser coagulation at the 1.07 μm wavelength is tested in the chicken chorio-allantoic membrane (CAM) model highlighting limitations reported in the archival literature. COMSOL based finite element models are presented which includes hypothetical limitations in coagulation during laser irradiation. Laser fluence rate and dosimetry are adjusted based on experimental OCT imaging and angiography observations as well as COMSOL models to test the hypothesis that blood shear stress and flow velocity are important challenges for laser coagulation and hemostasis of large vessels