Compliance of peripheral airways deduced from morphometry.

Area of Science:

• Respiratory Physiology
• Pulmonary Mechanics
• Airway Remodeling

Background:

• Understanding airway mechanics is crucial for respiratory health.
• Airway smooth muscle contraction, induced by agents like carbachol, significantly impacts lung function.
• Previous studies suggest epithelial folds play a role in airway collapse dynamics.

Purpose of the Study:

• To investigate the effects of varying positive end-expiratory pressure (PEEP) on airway morphometry in rabbits.
• To compare airway mechanics in carbachol-treated versus saline-treated (sham) rabbits.
• To elucidate the relationship between airway wall thickness, lumen pressure, and collapse behavior.

Main Methods:

• Rabbit lungs were fixed at different PEEP levels (10 to -4 cmH2O) after carbachol or saline treatment.
• Morphometric analysis of membranous bronchioles was performed on fixed lung tissue.
• Airway lumen area and shape changes were measured under varying PEEP conditions.

Main Results:

• Carbachol-treated airways showed expected lumen area reduction with decreasing PEEP, unlike sham-treated airways.
• Sham-treated airways remained open until PEEP between 4 and 2 cmH2O, then collapsed into an oval shape.
• Carbachol-treated airways exhibited oval collapse at a much lower PEEP of -4 cmH2O.
• Smaller airways with thicker walls demonstrated less collapse than larger airways.

Conclusions:

• Airway smooth muscle constriction significantly alters lung recoil pressure effects on airway caliber.
• Airway wall thickness-to-radius ratio is a key determinant of airway resistance to buckling and collapse.
• Findings support the hypothesis that peribronchial stress exceeds lumen pressure during airway ovalization.