Effect of airway closure on ventilation distribution

Area of Science:

• Pulmonary Physiology
• Respiratory Mechanics

Background:

• Ventilation distribution is crucial for efficient gas exchange.
• Airway closure, particularly at lower lung volumes, can impair ventilation.
• Understanding the impact of airway closure on ventilation inhomogeneity is important for respiratory health.

Purpose of the Study:

• To investigate the effect of airway closure on ventilation distribution during tidal breathing.
• To determine if end-inspiratory breath holds can mitigate ventilation maldistribution caused by airway closure.

Main Methods:

• Multiple-breath nitrogen washouts (MBNW) were performed in six normal subjects.
• Measurements were taken at various pre-inspiratory lung volumes (PILV), including below closing capacity.
• Ventilation maldistribution was assessed using normalized phase III slope (Snf) and alveolar mixing efficiency.

Main Results:

• Ventilation maldistribution, indicated by increased Snf and decreased alveolar mixing efficiency, worsened significantly as lung volumes decreased below closing capacity.
• Short end-inspiratory breath holds (2-5 seconds) at lung volumes below closing capacity markedly improved ventilation distribution, reducing Snf and increasing mixing efficiency.
• These improvements suggest that inhomogeneous airway closure in the lung periphery is a primary factor in ventilation inequality at low lung volumes.

Conclusions:

• Airway closure significantly increases ventilation inequality during tidal breathing.
• Short end-inspiratory breath holds are an effective strategy to improve ventilation distribution in the presence of airway closure.
• Inhomogeneous closure of peripheral airways is the main driver of ventilation maldistribution below closing capacity.