  Pulmonary hypertension (PH) is a debilitating disease that includes five main
subgroups, but only one is curable: chronic thromboembolic pulmonary
hypertension (CTEPH). CTEPH is caused by recurrent or unresolved pulmonary
thromboemboli, leading to perfusion defects and increased arterial wave
reflections. CTEPH treatment depends on lesion location and severity, and
patients with distal lesions are inoperable by standard surgical intervention.
Instead, they are treated with balloon pulmonary angioplasty (BPA), a
multi-session surgery that disrupts the thromboembolic material using a
catheter balloon. The goal of BPA is to reduce pulmonary arterial pressure and
reestablish adequate blood flow to all regions of the lung. However, there
still lacks an integrative, holistic tool for identifying target lesions for
optimal treatment. To address this insufficiency, we provide a proof of concept
study simulating CTEPH hemodynamics and BPA therapy using a multiscale,
one-dimensional (1D) fluid dynamics model. The large pulmonary arterial
geometry is derived from a computed tomography (CT) image, whereas a structured
tree represents the small vessels. We model ring- and web-like lesions, common
in CTEPH, using two pressure-loss terms. We simulate normotensive conditions
and four CTEPH disease scenarios; the latter includes 20 large artery lesions
and introduces both local and global vascular remodeling. BPA therapy is
simulated by simultaneously reducing lesion severity in three locations. Our
predictions mimic severe CTEPH, manifested by an increase in mean proximal
pulmonary arterial pressure above 20 mmHg and prominent wave reflections. Both
flow and pressure decrease in vessels distal to the lesions and increase in
unobstructed vascular regions. We use the main pulmonary artery pressure, a
wave reflection index, and a measure of flow heterogeneity to select optimal
target lesions for BPA.
