CFD simulation of the airflow through the human respiratory tract

This study compares the effect of extra-thoracic airways (ETA) on the flow field through the lower airways by carrying out simulations of the airflow through the human respiratory tract. Three geometries, consisting of the ETA, CT-derived lower airway, and a combination of the two were utilized in simulations that were performed for transient breathing in addition to constant inspiration/expiration. Physiologically-appropriate regional ventilation for two different flow rates was induced at the distal boundaries by imposing appropriate lobar specific flow rates. Two breathing rates were considered, i.e., 7.5 and 15 breaths per minute with a tidal volume of 0.5 liter. For comparison, the flow rates for constant inspiration/expiration were selected to be identical to the peak flow rates during the transient breathing. Significant differences indicate that simulations that utilize constant inspiration or expiration may not be appropriate for gaining insight into the flow patterns through the human airways

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

Abstract 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