Model analysis of gas distribution within human lung acinus

Area of Science:

• Pulmonary Physiology
• Computational Biology
• Respiratory System Mechanics

Background:

• Gas exchange in the lungs relies on efficient mixing of inspired air with residual gases in the alveoli.
• Previous models often simplify lung acinar structure, potentially underestimating intra-acinar gas distribution complexities.
• Understanding alveolar gas concentration inhomogeneity is crucial for diagnosing respiratory diseases.

Purpose of the Study:

• To simulate alveolar gas concentrations in an asymmetrically branching human lung acinus model.
• To quantify the degree of oxygen (O2) inhomogeneity resulting from convection and diffusion.
• To compare model-derived inhomogeneity with in vivo measurements of gas mixing.

Main Methods:

• Developed an expansile model of a human lung acinus based on morphometric data.
• Solved differential equations for simultaneous convection and molecular diffusion during a 1-liter O2 breath.
• Analyzed O2 concentrations and calculated inspired gas per unit volume post-inspiration, including breath-hold scenarios.

Main Results:

• A 1-liter breath simulation predicted substantial O2 inhomogeneity, with a twofold range in inspired gas per unit volume.
• Even a 10-second breath hold did not homogenize alveolar O2 concentrations.
• Increased ventilation (60 l/min) amplified inhomogeneity by 50%; diffusive pendelluft contributed minimally to the alveolar plateau.

Conclusions:

• Intra-acinar gas inhomogeneity is significant in a realistic lung acinus model, even with homogeneous volume changes.
• The simulated inhomogeneity is considerably less than that inferred from whole-lung measurements.
• Intra-acinar inhomogeneity likely represents a small fraction of the total gas mixing impairment observed in vivo.