Analysis of Cerebral Aneurysm Wall Tension and Enhancement Using Finite Element Analysis and High-Resolution Vessel Wall Imaging.

Biomechanical computational simulation of intracranial aneurysms has become a promising method for predicting features of instability leading to aneurysm growth and rupture. Hemodynamic analysis of aneurysm behavior has helped investigate the complex relationship between features of aneurysm shape, morphology, flow patterns, and the proliferation or degradation of the aneurysm wall. Finite element analysis paired with high-resolution vessel wall imaging can provide more insight into how exactly aneurysm morphology relates to wall behavior, and whether wall enhancement can describe this phenomenon. In a retrospective analysis of 23 unruptured aneurysms, finite element analysis was conducted using an isotropic, homogenous third order polynomial material model. Aneurysm wall enhancement was quantified on 2D multiplanar views, with 14 aneurysms classified as enhancing (CRstalk≥0.6) and nine classified as non-enhancing. Enhancing aneurysms had a significantly higher 95th percentile wall tension (µ = 0.77 N/cm) compared to non-enhancing aneurysms (µ = 0.42 N/cm, p < 0.001). Wall enhancement remained a significant predictor of wall tension while accounting for the effects of aneurysm size (p = 0.046). In a qualitative comparison, low wall tension areas concentrated around aneurysm blebs. Aneurysms with irregular morphologies may show increased areas of low wall tension. The biological implications of finite element analysis in intracranial aneurysms are still unclear but may provide further insights into the complex process of bleb formation and aneurysm rupture.

Flow Monitoring of ECMO Circuit for Detecting Oxygenator Obstructions.

Oxygenator thrombosis during extracorporeal membrane oxygenation (ECMO), is a complication that necessitates component replacement. ECMO centers monitor clot burden by intermittent measurement of pressure drop across the oxygenator. An increase in pressure drop at a preset flow rate suggests an increase in resistance/clot formation within the oxygenator. This monitoring method comes with inherent disadvantages such as monitoring gaps, and increased risk of air embolism and infection. We explored utilizing flow measurement, which avoids such risks, as an indicator of ECMO circuit obstructions. The hypothesis that flow rate through a shunt tube in the circuit will increase as distal resistances in the circuit increases was tested. We experimentally simulated controlled levels of oxygenator obstructions using glass microspheres in an ex vivo veno-venous ECMO circuit and measured the change in shunt flow rate using over the tube ultra-sound flow probes. A mathematical model was also used to study the effect of distal resistances in the ECMO circuit on shunt flow. Results of both the mathematical model and the experiments showed a clear and measurable increase in shunt flow with increasing levels of oxygenator obstruction. Therefore, flow monitoring appears to be an effective non-contact and continuous method to monitor for obstruction during ECMO.

Electrochemical Approach to Measure Physiological Fluid Flow Rates.

In vivo measurement of the flow rate of physiological fluids such as the blood flow rate in the heart is vital in critically ill patients and for those undergoing surgical procedures. The reliability of these measurements is therefore quite crucial. However, current methods in practice for measuring flow rates of physiological fluids suffer from poor repeatability and reliability. Here, we assessed the feasibility of a flow rate measurement method that leverages time transient electrochemical behavior of a tracer that is injected directly into a medium (the electrochemical signal caused due to the tracer injectate will be diluted by the continued flow of the medium and the time response of the current-the electrodilution curve-will depend on the flow rate of the medium). In an experimental flow loop apparatus equipped with an electrochemical cell, we used the AC voltammetry technique and tested the feasibility of electrodilution-based measurement of the flow rate using two mediums-pure water and anticoagulated blood-with 0.9 wt% saline as the injectate. The electrodilution curve was quantified using three metrics-change in current amplitude, total time, and change in the total charge for a range of AC voltammetry settings (peak voltages and frequencies). All three metrics showed an inverse relationship with the flow rate of water and blood, with the strongest negative correlation obtained for change in current amplitude. The findings are a proof of concept for the electrodilution method of the flow rate measurement and offer the potential for physiological fluid flow rate measurement in vivo.