Modeling Heat Transfer in the Eye during Cataract Surgery

Cataract surgery is one of the most commonly performed surgical procedures in the world, and it involves using a technique called phacoemulsification. With this technique, the cloudy, crystalline lens in the eye is mechanically disrupted using a probe that vibrates at an ultrasonic frequency. However, this vibrating tip mechanism leads to frictional heat generation, which can potentially cause extensive thermal damage to fragile tissue structures surrounding the lens. In order to minimize damage due to this frictional heat, a coolant is typically used while the phaco probe is in operation. In this report, our goal is to model heat transfer in the eye using COMSOL Multiphysics software in three different scenarios: (1) under normal physiological conditions, (2) considering only the frictional heat generation from the phaco probe, (3) and considering both heat generation as well as heat removal by the coolant. Using a 2-D axisymmetric geometry to model the eye structure, we determined that using the heat source by itself results in temperatures far above the threshold of 328 K for thermal wound injury. However, with the addition of the coolant for heat removal, temperatures in the iris were lowered to less than 320 K, thereby reducing any thermal burn risk to the patient. Further analysis demonstrated that decreasing the coolant temperature or decreasing the probe?s operational power can significantly improve the safety of the procedure

Computational fluid dynamics of developing avian outflow tract heart valves

Hemodynamic forces play an important role in sculpting the embryonic heart and its valves. Alteration of blood flow patterns through the hearts of embryonic animal models lead to malformations that resemble some clinical congenital heart defects, but the precise mechanisms are poorly understood. Quantitative understanding of the local fluid forces acting in the heart has been elusive because of the extremely small and rapidly changing anatomy. In this study, we combine multiple imaging modalities with computational simulation to rigorously quantify the hemodynamic environment within the developing outflow tract (OFT) and its eventual aortic and pulmonary valves. In vivo Doppler ultrasound generated velocity profiles were applied to Micro-Computed Tomography generated 3D OFT lumen geometries from Hamburger-Hamilton (HH) stage 16-30 chick embryos. Computational fluid dynamics simulation initial conditions were iterated until local flow profiles converged with in vivo Doppler flow measurements. Results suggested that flow in the early tubular OFT (HH16 and HH23) was best approximated by Poiseuille flow, while later embryonic OFT septation (HH27, HH30) was mimicked by plug flow conditions. Peak wall shear stress (WSS) values increased from 18.16 dynes/cm(2) at HH16 to 671.24 dynes/cm(2) at HH30. Spatiotemporally averaged WSS values also showed a monotonic increase from 3.03 dynes/cm(2) at HH16 to 136.50 dynes/cm(2) at HH30. Simulated velocity streamlines in the early heart suggest a lack of mixing, which differed from classical ink injections. Changes in local flow patterns preceded and correlated with key morphogenetic events such as OFT septation and valve formation. This novel method to quantify local dynamic hemodynamics parameters affords insight into sculpting role of blood flow in the embryonic heart and provides a quantitative baseline dataset for future research