Search

In this study the regulation of vascular tone inducing the blood flow increase at the onset\ud of exercise is examined. Therefore, our calf circulation model was extended with a regulation\ud model to simulate changes in vascular tone depending on myogenic, metabolic\ud and baroreflex regulation. The simulated blood flow corresponded to the in vivo response\ud and it was concluded that metabolic activation caused the flow increase shortly\ud after muscle contraction. Secondly, the change in baseline flow upon tilt was a result of\ud myogenic and baroreflex activation. Based on a sensitivity analysis the myogenic gain\ud was identified as most important parameter.\ud

Vascular access dysfunction is one of the main causes of morbidity and hospitalization in hemodialysis patients. This major clinical problem points out the need for prediction of hemodynamic changes induced by vascular access surgery. Here we reviewed the potential of a patient-specific computational vascular network model that includes vessel wall remodeling to predict blood flow change within 6 weeks after surgery for different arteriovenous fistula configurations. For model validation, we performed a multicenter, prospective clinical study to collect longitudinal data on arm vasculature before and after surgery. Sixty-three patients with newly created arteriovenous fistula were included in the validation data set and divided into four groups based on fistula configuration. Predicted brachial artery blood flow volumes 40 days after surgery had a significantly high correlation with measured values. Deviation of predicted from measured brachial artery blood flow averaged 3% with a root mean squared error of 19.5%, showing that the computational tool reliably predicted patient-specific blood flow increase resulting from vascular access surgery and subsequent vascular adaptation. This innovative approach may help the surgeon to plan the most appropriate fistula configuration to optimize access blood flow for hemodialysis, potentially reducing the incidence of vascular access dysfunctions and the need of patient hospitalization.

Uncertainty quantification and global sensitivity analysis are indispensable for patient-specific applications of models that enhance diagnosis or aid decision-making. Variance-based sensitivity analysis methods, which apportion each fraction of the output uncertainty (variance) to the effects of individual input parameters or their interactions, are considered the gold standard. The variance portions are called the Sobol sensitivity indices and can be estimated by a Monte Carlo (MC) approach (e.g., Saltelli's method [1]) or by employing a metamodel (e.g., the (generalized) polynomial chaos expansion (gPCE) [2, 3]). All these methods require a large number of model evaluations when estimating the Sobol sensitivity indices for models with many parameters [4]. To reduce the computational cost, we introduce a two-step approach. In the first step, a subset of important parameters is identified for each output of interest using the screening method of Morris [5]. In the second step, a quantitative variance-based sensitivity analysis is performed using gPCE. Efficient sampling strategies are introduced to minimize the number of model runs required to obtain the sensitivity indices for models considering multiple outputs. The approach is tested using a model that was developed for predicting post-operative flows after creation of a vascular access for renal failure patients. We compare the sensitivity indices obtained with the novel two-step approach with those obtained from a reference analysis that applies Saltelli's MC method. The two-step approach was found to yield accurate estimates of the sensitivity indices at two orders of magnitude lower computational cost. Copyright © 2015¿John Wiley & Sons, Ltd.

When the wall of a blood vessel is damaged, the immediate response of the body to prevent blood loss is the creation of a platelet plug. The process is both chemical (platelets are chemically activated to adhere to the injured wall) and mechanical (platelets are convected by blood flow, which interacts with the forming plug). A continuum model for platelet plug formation and growth is presented in this work, which allows to study the interaction between platelet plug morphology and local haemodynamics. The numerical framework consists of two parts: a biochemical model combined with a new plug growth model. The biochemical model is a system of convection-diffusion-reaction equations, each of which represents the dynamics of platelets and chemicals involved in the plug formation process. The plug growth model defines the plug interface displacement based on the outcome of the biochemical model, that is, on the number of deposited bounded platelets on the injured part of the vessel wall. Results for different cases are shown, together with a comparison between the sole biochemical model and the complete model that includes plug growth. The framework opens the way to the development of continuum models for full blood clot formation and growth in physiologically relevant configurations.