Morphometric estimates of diffusing capacity in lungs fixed under zone II and zone III conditions

Area of Science:

• Pulmonary Physiology
• Comparative Anatomy

Background:

• Diffusing capacity (DL) is crucial for gas exchange in the lungs.
• Previous studies utilized instillation-fixed lungs for morphometric DL estimates.

Purpose of the Study:

• To compare morphometric estimates of pulmonary diffusing capacity (DL) in rabbit lungs under different physiological conditions.
• To re-evaluate the interpretation of DL estimates from instillation-fixed lungs.

Main Methods:

• Comparative morphometry was employed on rabbit lungs.
• Lungs were fixed via vascular perfusion (zone II and III) and airway instillation.
• Diffusing capacity (DL) was estimated morphometrically.

Main Results:

• Zone II lungs exhibited a 25% lower DL (0.074 ml·sec⁻¹·mbar⁻¹) compared to instillation-fixed lungs (0.102 ml·sec⁻¹·mbar⁻¹).
• Zone III lungs showed DL values comparable to instillation-fixed lungs.
• DL varied regionally within zone III lungs, increasing vertically.

Conclusions:

• Vascular perfusion fixation, simulating zone II conditions, reduces DL estimates.
• Morphometric DL estimates from instillation-fixed lungs may not represent an unattainable physiological limit.
• Regional variations in DL within the lung must be considered.