Energetics and hemodynamic changes of normal and various right heart bypass (Fontan) circulations in lambs under varying respiration parameters.

The Fontan circulation or one of its many modifications is a common surgical procedure implemented in children with congenital heart defects to improve pulmonary circulation. Two modifications are the atriopulmonary connection (AP) and the modified total cavopulmonary connection (TCPC). Successful AP and TCPC operations performed in lambs show respiration has a major influence on systemic and pulmonary hemodynamics. Instantaneous pressure and flow waveforms are obtained before and after the procedure and energies are calculated. Hemodynamic changes in relevant vessels are also acquired. Time delays due to respiration will be calculated and transfer functions computed. The purpose of this study is to examine these waveforms and energy gains/losses under varying respiration parameters in order to aid in determining an optimal surgical protocol as well as assist in the development an accurate computer simulation model.

The effect of incorporating vessel compliance in a computational model of blood flow in a total cavopulmonary connection (TCPC) with caval centerline offset.

BACKGROUND: The total cavopulmonary connection (TCPC), a palliative correction for congenital defects of the right heart, is based on the corrective technique developed by Fontan and Baudet. Research into the TCPC has primarily focused on reducing power loss through the connection as a means to improve patient longevity and quality of life. The goal of our study is to investigate the efficacy of including a caval offset on the hemodynamics and, ultimately, power loss of a connection. As well, we will quantify the effect of vessel wall compliance on these factors and, in addition, the distribution of hepatic blood to the lungs. METHODS: We employed a computational fluid dynamic model of blood flow in the TCPC that includes both the non-Newtonian shear thinning characteristics of blood and the nonlinear compliance of vessel tissue. RESULTS: Power loss in the rigid-walled simulations decayed exponentially as caval offset increased. The compliant-walled results, however, showed that after an initial substantial decrease in power loss for offsets up to half the caval diameter, power loss increased slightly again. We also found only minimal mixing in both simulations of all offset models. CONCLUSIONS: The increase in power loss beyond an offset of half the caval diameter was due to an increase in the kinetic contribution. Reduced caval flow mixing, on the other hand, was due to the formation of a pressure head in the offset region which acts as a barrier to flow.

Transendoscopic neodymium:yttrium aluminum garnet laser irradiation in horses.

A neodymium:yttrium aluminum garnet (Nd:YAG) laser was used to study effects of applying laser irradiation transendoscopically to the corniculate process of the arytenoid cartilage in horses. Dosimetry was established initially in vitro in 10 corniculate cartilages that were irradiated and examined histologically to determine penetration depths at selected power settings. Eleven horses were given xylazine IV and butorphoral tartrate IV, and their left ventricle and corniculate process were irradiated. Six horses had left laryngeal hemiplegia and were euthanatized and necropsied 14 weeks after laser application and evaluation for upper airway stridor. Endoscopy was performed in the 5 other horses; they were euthanatized and necropsied at selected intervals to characterize the healing process. Healing was by second intention and was complete at 14 weeks. Two horses developed buds of granulation tissue along the laser incision, which resolved after a second laser application. Scar tissue formation resulted in left of midline displacement of the dorsal portion of the right corniculate process. The left ventricle healed without complications and was totally ablated. All horses had inspiratory stridor when exercised 14 weeks after laser irradiation.