Pulmonary Tree Hemodynamics in Pediatric Pulmonary Arterial Hypertension

When 3D patient-specific flow simulations for the proximal pulmonary arteries (PAs) are combined with a disease-adapted morphometric pulmonary tree model, wall shear stress (WSS) decreases significantly in the main PA but increases significantly in the distal PAs in patients with severe pulmonary arterial hypertension (PAH) compared with control patients.

Researchers conducted a retrospective study that used data from patients who were treated at Lucile Packard Children’s Hospital at Stanford University in California, during a 15-year period. Results of the study were published in Biomechanics and Modeling in Mechanobiology.

The purpose of the study was to characterize WSS and wall strain in individuals <18 years of age with PAH at different stages of disease severity with the use of computational patient-specific modeling. Computed tomography, magnetic resonance imaging, and right heart catheterization data were obtained and integrated into PA models for patients both with and without PAH. 

All participants were divided into 3 PAH severity groups (control, moderate, and severe), according to clinical assessments. Hemodynamics and wall strains were quantified with the use of a finite element solver. A morphometric tree model was developed to estimate WSS in the distal small PAs, with diameters ranging from 50 to 500 µm, and inputs were derived from outlets of the 3D model. A total of 10 pediatric patients with PAH were simulated.

Results demonstrated that WSS in the proximal PAs decreased significantly, based on disease severity (control, 20.5 dyn/cm²; moderate, 15.8 dyn/cm²; severe, 6.3 dyn/cm²; P <.05). Moreover, oscillatory shear index increased significantly in the main PA based on disease severity (control, 0.13; moderate, 0.13; severe, 0.2; P <.05). In addition, oscillatory shear index increased in the severe PAH group (mean, 0.2) compared with control patients (mean, 0.13; P =.05) and those with moderate PAH (mean, 0.13; P =.04). Mean WSS for the distal PAs between 100 and 500 µm increased significantly according to severity of PAH (control, 20 dyn/cm²; moderate, 52 dyn/cm²; severe, 116 dyn/cm²; P <.05).

Because only 10 pediatric patients with PAH were simulated, it is likely that this small sample size does not fully represent the wide spectrum of PAH conditions.

Nonetheless, the investigators concluded that 3D flow simulations have demonstrated that WSS is decreased significantly in the main PA, based on disease severity, whereas the mathematical morphometric model is suggestive of increased WSS in the distal small vessels. The use of computational pulmonary models can reveal mechanical stimuli that act on vessel walls, thus informing risk stratification in patients with PAH and flow shear experiments.

Reference

Yang W, Dong M, Rabinovitch M, Chan FP, Marsden AL, Feinstein JA. Evolution of hemodynamic forces in the pulmonary tree with progressively worsening pulmonary arterial hypertension in pediatric patients [published online January 12, 2019]. Biomech Model Mechanobiol. doi:10.1007/s10237-018-01114-0