Diffusion-convection equation solved in parallel regions of the lung

Area of Science:

• Pulmonary physiology
• Respiratory mechanics
• Gas exchange

Background:

• The single path model of airway gas transport is crucial for understanding lung function.
• Evaluating the impact of time on gas fractions within the lungs is essential for respiratory research.

Purpose of the Study:

• To evaluate the efficacy of a single path model in predicting airway gas transport during various respiratory maneuvers.
• To assess the model's ability to simulate gas fractions and expirograms under different breathing conditions, including breath-holding.

Main Methods:

• Incorporated a single path model of airway gas transport.
• Simulated two experimental maneuvers: a fast inhalation/exhalation with breath-holding and a standard single-breath nitrogen washout test.
• Compared model predictions with experimental data for argon and nitrogen washout.

Main Results:

• The model predicted expired argon and nitrogen within a 3% error for non-breath-holding conditions.
• Breath-holding predictions deviated from experimental results due to the model's assumption of even alveolar mixing.
• The model generated a four-phase nitrogen expirogram but failed to sharply distinguish between phase 3 and phase 4.

Conclusions:

• Uneven emptying of parallel lung regions, rather than alveolar stratification, generates the expirogram phases.
• Alveolar gas stratification during inspiration dissipates by the end of the maneuver.
• The current anatomical model is insufficient for accurately predicting breath-holding maneuvers.