Vascular tree structure affects lung blood flow heterogeneity simulated in three dimensions

Area of Science:

• Physiology
• Biophysics
• Computational Biology

Background:

• Pulmonary arterial tree structure is crucial for efficient blood distribution.
• Understanding blood flow heterogeneity is key to pulmonary circulation research.
• Previous models have simplified vascular branching patterns.

Purpose of the Study:

• To simulate pulmonary arterial tree structures to investigate blood flow heterogeneity.
• To analyze the impact of branching parameters on flow distribution and fractal properties.
• To compare simulation results with experimental observations in pulmonary circulation.

Main Methods:

• A symmetrical, bifurcating 3D model of the pulmonary arterial tree was developed.
• Simulations included 11 generations with defined branch angle (Theta), length ratio (rL), rotation (phi), and flow fraction (gamma).
• Generated tree structures were analyzed in 1-cm³ samples for blood flow relative dispersion (RD%) and fractal dimensions (Ds).

Main Results:

• Simulated trees exhibited blood flow relative dispersions (RD%) of 42-52% and fractal dimensions (Ds) of 1.15-1.20, even with equal branch flows.
• Unequal flow partitioning (gamma ≠ 0.5) increased RD% and altered Ds based on flow bias.
• Biased flow assignment led to increased blood flow gradients and a negative correlation between flow and distance only when gamma ≠ 0.5.

Conclusions:

• Recursive branching vascular tree simulations replicate experimental pulmonary blood flow heterogeneity.
• Differences in terminal arteriole density per sample contribute to observed heterogeneity.
• Unequal blood flow partitioning at branch points is essential for generating realistic blood flow gradients and distance correlations.