RESUMEN

Recent clinical studies have reported that heart failure with preserved ejection fraction (HFpEF) can be divided into two phenotypes based on the range of ejection fraction (EF), namely HFpEF with higher EF and HFpEF with lower EF. These phenotypes exhibit distinct left ventricle (LV) remodelling patterns and dynamics. However, the influence of LV remodelling on various LV functional indices and the underlying mechanics for these two phenotypes are not well understood. To address these issues, this study employs a coupled finite element analysis (FEA) framework to analyse the impact of various ventricular remodelling patterns, specifically concentric remodelling (CR), concentric hypertrophy (CH), and eccentric hypertrophy (EH), with and without LV wall thickening on LV functional indices. Further, the geometries with a moderate level of remodelling from each pattern are subjected to fibre stiffening and contractile impairment to examine their effect in replicating the different features of HFpEF. The results show that with severe CR, LV could exhibit the characteristics of HFpEF with higher EF, as observed in recent clinical studies. Controlled fibre stiffening can simultaneously increase the end-diastolic pressure (EDP) and reduce the peak longitudinal strain (ell) without significant reduction in EF, facilitating the moderate CR geometries to fit into this phenotype. Similarly, fibre stiffening can assist the CH and 'EH with wall thickening' cases to replicate HFpEF with lower EF. These findings suggest that potential treatment for these two phenotypes should target the bio-origins of their distinct ventricular remodelling patterns and the extent of myocardial stiffening.

Asunto(s)

Insuficiencia Cardíaca , Modelos Cardiovasculares , Remodelación Ventricular , Remodelación Ventricular/fisiología , Humanos , Insuficiencia Cardíaca/fisiopatología , Fenotipo , Volumen Sistólico/fisiología , Ventrículos Cardíacos/fisiopatología , Ventrículos Cardíacos/diagnóstico por imagen , Simulación por Computador

RESUMEN

This paper presents a lattice Boltzmann framework for the transient simulation of blood flow using biologically inspired geometries and pressure boundary conditions. The Kuang-Luo rheological model is used to represent blood as a homogeneous continuum. This model includes the two primary non-Newtonian characteristics of blood, namely viscoplasticity and pseudoplasticity. This paper makes two contributions. First, the numerical challenges associated with zero strain rates and infinite viscosity, as a consequence of the yield stress in the Kuang-Luo model, were addressed by regularising the constitutive equation so that the viscosity tends towards a finite value at low strain rates. A two-relaxation-time operator, which exhibits improved performance over the single-relaxation-time operator and lower computational overhead than the multiple-relaxation-time operator, is employed in the collision process. The recursive relationship between the local strain rate and relaxation rate was addressed by use of an implicit solver for these two quantities. The implemented model was benchmarked against analytic solutions for Poiseuille flow between parallel plates in two dimensions and in a cylindrical tube in three dimensions. More importantly, the transient performance of the implemented model was demonstrated by matching the predicted start-up flow of the Poiseuille flow of a Bingham fluid with the corresponding analytical solution. Second, the numerical developments were applied in the simulation of transient blood flow in complex configurations. The development and implementation of physically inspired pressure profiles highlighted the shortcomings of using a sinusoidal pressure profile in the prediction of velocity and stress distributions. Finally, the simulation of blood flow in a section of a carotid artery indicated a number of flow characteristics that will be of interest to future investigations of clinical problems.

Asunto(s)

Arterias Carótidas , Velocidad del Flujo Sanguíneo , Simulación por Computador , Reología , Viscosidad

RESUMEN

A comprehensive understanding of gas flow in long hollow-core photonic crystal fibers (HC-PCFs) is critical for evaluating their sensing performance for low-concentration gases, especially in terms of response time. The aim of this paper is to numerically and experimentally investigate the pressure-driven gas flow dynamics in a relatively long HC-PCF-based gas sensor. The gas flow in the core of a 1.1 m long HC-PCF was numerically modeled to examine the gas sensing response time in terms of the time for the gas to fill the core (gas filling time). The model was validated against the experimental results of continuous-wave modulated photothermal spectroscopy. The model was then used to analyze the effects of gas inlet pressure, core diameter, fiber length, and gas type on the gas flow field and gas filling time. The results revealed that a lower gas filling time was achieved as the pressure difference between the inlet and outlet increased, the core diameter increased, and/or the core length decreased. The developed numerical model provides valuable information such as cross-sectional velocity profiles and gas flow rates that cannot be readily obtained from simpler analytical models.