  Chronic thromboembolic pulmonary hypertension (CTEPH) is caused by recurrent
or unresolved pulmonary thromboemboli, leading to perfusion defects and
increased arterial wave reflections. CTEPH treatment aims to reduce pulmonary
arterial pressure and reestablish adequate lung perfusion, yet patients with
distal lesions are inoperable by standard surgical intervention. Instead, these
patients undergo balloon pulmonary angioplasty (BPA), a multi-session,
minimally invasive surgery that disrupts the thromboembolic material within the
vessel lumen using a catheter balloon. However, there still lacks an
integrative, holistic tool for identifying optimal target lesions for
treatment. To address this insufficiency, we simulate CTEPH hemodynamics and
BPA therapy using a multiscale fluid dynamics model. The large pulmonary
arterial geometry is derived from a computed tomography (CT) image, whereas a
fractal tree represents the small vessels. We model ring- and web-like lesions,
common in CTEPH, and simulate normotensive conditions and four CTEPH disease
scenarios; the latter includes both large artery lesions and 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 (MPA) pressure, a wave reflection index, and a measure of flow
heterogeneity to select optimal target lesions for BPA. In summary, this study
provides a multiscale, image-to-hemodynamics pipeline for BPA therapy planning
for inoperable CTEPH patients.
