Although catheters with side holes allow high flow rate during hemodialysis, they also induce flow disturbances and create a critical hemodynamic environment that can favor fibrin deposition and thrombus formation. This study compared the blood flow and analyzed the influence of shear stress and shear rate in fibrin deposition and thrombus formation in nontunneled hemodialysis catheters with unobstructed side holes (unobstructed device) or with some side holes obstructed by blood thrombi (obstructed device). Computational fluid dynamics (CFD) was performed to simulate realistic blood flow under laminar and turbulent conditions. The results from the numerical simulations were compared with the fibrin distribution and thrombus architecture data obtained from scanning electron microscopy (SEM) and two photons laser scanning microscopy (TPLSM) on human thrombus formed in catheters removed from patients. CFD showed that regions of flow eddies and separation were mainly found in the venous holes region. TPLSM characterization of thrombi and fibrin structure in patient samples showed fibrin formations in accordance with simulated flux dynamics. Under laminar flow conditions, the wall shear stress close to border holes increased from 87.3±0.2 Pa in the unobstructed device to 176.2±0.5 Pa in the obstructed one. Under turbulent flow conditions, the shear stress increased by 47% when comparing the obstructed to the unobstructed catheter. The shear rates were generally higher than 5000/s and therefore sufficient to induce fibrin deposition. This findings were supported by SEM data documenting a preferential fibrin arrangement on side hole walls.

The use of porcine or bovine pericardium biological cardiac valves has as its main disadvantage a relatively short lifespan, with failures due to calcification and fatigue. Increasing these valves' durability constitutes a great challenge. An understudied phenomenon is the effect of flutter, an oscillation of the leaflets that can cause regurgitation and accelerate calcification and fatigue. As a starting point to study how to reduce or prevent these oscillations, a method was developed to quantify the flutter frequencies occurring at the point of the valve's full opening. On a test bench that simulates the heart flow, the cusp behaviors of eight biological valves were filmed with a high speed camera at 2000 frames per second at different flow rates and motion capture software obtained the frequencies and amplitudes of the vibrations of each leaflet. Oscillations in the range of 200 Hz with average amplitudes of 0.4 mm were found; larger nominal diameter valves obtained lower values, and bovine pericardial valves had superior performance compared to porcine valves. A dimensionless analysis was performed to find a relationship between the geometric and mechanical properties of the valves with the critical speed of the onset of fluttering. This relationship inspired a method to predict whether flutter will occur in the bioprosthesis. This method is a new tool for the consideration of maximizing the life of prosthetic valves.

Integration of SEM and TPLSM was found to be an excellent tool for characterizing thrombi in hemodialysis CVC removed from patients. Protocols and techniques presented here may be useful in the development and testing of new strategies for limiting thrombus formation on vascular access because of CVC.

No abstract

The analytical method presented here proved to be a rapid and effective way for quantifying fibrin content in thrombi formed on CVCs with potential application in future clinical studies.