Species-Specific Pulmonary Arterial Asymmetry Determines Species Differences in Regional Pulmonary Perfusion

Abstract

The functional significance of differences in pulmonary vascular branching and diameter asymmetry between the human and quadruped lung has not previously been addressed. To evaluate the contribution of branching asymmetry to observable species differences in blood flow gradients, computed distributions of blood flow were compared in structure-based models of the human and ovine pulmonary arteries. The models were derived using a combination of computed tomography and a volume-filling algorithm. Pressure, flow, and deformed vessel diameter were calculated in both species models using equations representing conservation of mass and momentum, and a pressure–diameter relationship. The major difference between the human and ovine results was the presence of a large region of “zone 4” flow and higher mean flows in the central region of the ovine lung compared to that in the human. Heterogeneity in tissue perfusion and the contribution of gravity were similar in both species models; however, the gravitationally directed gradients of perfusion in the human and ovine models were different and each consistent with human and quadruped measurements, respectively. The results suggest that measured species differences in pulmonary perfusion gradients are largely determined by differences in branching asymmetry.

Pulmonary embolism: predicting disease severity

“…The model that is considered in the following section includes only the most important passive features of the pulmonary circulation; however, the contribution of active features can still be postulated based on the consistency or lack of consistency of predicted function compared with clinical measurements. Models of blood flow in the larger pulmonary blood vessels have used either a systems (electrical analogue) approach [40], or a physiological approach that solves flow equations in a more realistic geometry [15,[41][42][43][44]. Recently, threedimensional computational fluid dynamics (CFD) has been used to simulate blood flow in anatomically accurate models of pulmonary blood vessels [44].…”

“…The baseline model relies on geometrical and mathematical simplifications that are described in detail in previous studies, along with their implications on simulation results [3,13,15,42]. For example, the model does not include supernumerary arteries (SAs), which are small side branches that arise at a large branching angle from the conventional arteries (CAs) of the lung to supply the closest respiratory tissue [84] without following a matching portion of the bronchial tree.…”

“…The baseline model has previously been tested against perfusion measures such as PVR and flow gradients [15,42], but there is limited data available to validate the model in PE. Imaging of blood redistribution in human PE via CT will not be possible for ethical reasons; however, at the time of writing, we are conducting animal studies to obtain quantitative data on redistribution of perfusion and ventilation during inert and autologous clot preparations.…”

Efficient, Physiologically Realistic Lung Airflow Simulations

“…These include the sequential simulations of Nowak et al [7] and Zhang et al [8], the hybrid CFD/1-D model of Ma and Lutchen [9], and the partially resolved multigeneration models of Gemci et al [10] and De Backer et al [11]. Recently, Tian et al [12] have proposed a hybrid model composed of a fully resolved airway up to generation 3, followed by a single flowpath model for generations 4-15. Researchers at the University of Iowa [13] and the University of Auckland [14] have developed technologies for generating complete speciesspecific lung geometries based on space-filling algorithms for the airway branches. CFD simulations have been performed in which large portions of the airway region are fully resolved, and the lower airways are treated using a 1-D flow resistance model.…”

Comparison of generic and subject-specific models for simulation of pulmonary perfusion and forced expiration

“…It is very difficult-perhaps impossible-to reconcile these different observations without using a multiscale computational model. Microsphere studies cannot be conducted on humans; hence there are species differences in arterial tree asymmetry that influence the characteristic distribution of blood [18], in addition to any effects of posture via the subject being supine during imaging or administration of microspheres.…”