Temporal evolution of mechanical stimuli from vascular remodeling in response to the severity and duration of aortic coarctation in a preclinical model.

Coarctation of the aorta (CoA) is one of the most common congenital cardiovascular diseases. CoA patients frequently undergo surgical repair, but hypertension (HTN) is still common. The current treatment guideline has revealed irreversible changes in structure and function, yet revised severity guidelines have not been proposed. Our objective was to quantify temporal alterations in mechanical stimuli and changes in arterial geometry in response to the range of CoA severities and durations (i.e. age of treatment) seen clinically. Rabbits were exposed to CoA resulting in peak-to-peak blood pressure gradient (BPGpp) severities of ≤ 10, 10-20, and ≥ 20 mmHg for a duration of ~ 1, 3, or 20 weeks using permanent, dissolvable, and rapidly dissolvable sutures. Elastic moduli and thickness were estimated from imaging and longitudinal fluid-structure interaction (FSI) simulations were conducted at different ages using geometries and boundary conditions from experimentally measured data. Mechanical stimuli were characterized including blood flow velocity patterns, wall tension, and radial strain. Experimental results show vascular alternations including thickening and stiffening proximal to the coarctation with increasing severity and/or duration of CoA. FSI simulations indicate wall tension in the proximal region increases markedly with coarctation severity. Importantly, even mild CoA induced stimuli for remodeling that exceeds values seen in adulthood if not treated early and using a BPGpp lower than the current clinical threshold. The findings are aligned with observations from other species and provide some guidance for the values of mechanical stimuli that could be used to predict the likelihood of HTN in human patients with CoA.

Fluid-structure interaction modeling of lactating breast: Newtonian vs. non-Newtonian milk.

Breastfeeding is a highly dynamic and complex mechanism. The suckling process by the infant involves compression and intra-oral vacuum pressure, leading to milk expression from breast. The accumulated milk from the nipple varies depending on the milk properties and transient flow rate during the suckling cycle. Rheological studies on raw human milk indicate that milk has a non-Newtonian shear-thinning flow behavior. This study aims to investigate the effect of non-Newtonian milk on flow behavior through the breast ductal system using fluid-structure interaction (FSI) simulation. The results of the non-Newtonian effects on flow velocity and the volumetric flow rate of expressed milk are presented. The results show that non-Newtonian Carreau model is promising for the simulation of human milk flow through the breast ductal systems. Also, the results show that the non-Newtonian effects on the milk flow behavior appear for 30-35% of the suckling cycle. Therefore, the Newtonian model is acceptable for the purpose of numerical simulation.

Determining the thermal characteristics of breast cancer based on high-resolution infrared imaging, 3D breast scans, and magnetic resonance imaging.

For over the three decades, various researchers have aimed to construct a thermal (or bioheat) model of breast cancer, but these models have mostly lacked clinical data. The present study developed a computational thermal model of breast cancer based on high-resolution infrared (IR) images, real three-dimensional (3D) breast surface geometries, and internal tumor definition of a female subject histologically diagnosed with breast cancer. A state-of-the-art IR camera recorded IR images of the subject's breasts, a 3D scanner recorded surface geometries, and standard diagnostic imaging procedures provided tumor sizes and spatial locations within the breast. The study estimated the thermal characteristics of the subject's triple negative breast cancer by calibrating the model to the subject's clinical data. Constrained by empirical blood perfusion rates, metabolic heat generation rates reached as high as 2.0E04 W/m3 for normal breast tissue and ranged between 1.0E05-1.2E06 W/m3 for cancerous breast tissue. Results were specific to the subject's unique breast cancer molecular subtype, stage, and lesion size and may be applicable to similar aggressive cases. Prior modeling efforts are briefly surveyed, clinical data collected are presented, and finally thermal modeling results are presented and discussed.

Fluid-structure interaction modeling of lactating breast.

There are two theories for the dynamics of milk expression by the infant. One hypothesis is that milk expression is due to the negative pressure applied by the infant sucking; the alternative hypothesis is that the tongue movement and squeezing of nipple/areola due to mouthing is responsible for the extraction of milk from the nipple. In this study, 3-D two-way Fluid-Structure Interaction (FSI) simulations are conducted to investigate the factors that play the primary role in expressing milk from the nipple. The models include the solid deformation and periodic motion of the tongue and jaw movement. To obtain the boundary conditions, ultrasound images of the oral cavity and motion of the tongue movement during breastfeeding are extracted in parallel to the intra-oral vacuum pressure. The numerical results are cross-validated with clinical data. The results show that, while vacuum pressure plays an important role in the amount of milk removal, the tongue/jaw movement is essential for facilitating this procedure by decreasing the shear stress within the main duct in the nipple. The developed model can contribute to a better understanding of breastfeeding complications due to infant or breast abnormalities and for the design of medical devices such as breast pumps and artificial teats.

Numerical Simulation of Tidal Breathing Through the Human Respiratory Tract.

The objective of this study is to explore the complexity of airflow through the human respiratory tract by carrying out computational fluid dynamics simulation. In order to capture the detailed physics of the flow in this complex system, large eddy simulation (LES) is performed. The crucial step in this analysis is to investigate the impact of breathing transience on the flow field. In this connection, simulations are carried out for transient breathing in addition to peak inspiration and expiration. To enable a fair comparison, the flowrates for constant inspiration/expiration are selected to be identical to the peak flowrates during the transient breathing. Physiologically appropriate regional ventilation for two different flowrates is induced. The velocity field and turbulent flow features are discussed for both flowrates. The airflow through the larynx is observed to be significantly complex with high turbulence level, recirculation, and secondary flow while the level of turbulence decreases through the higher bifurcations.