Morphometric estimation of pulmonary diffusion capacity in two horse lungs

Area of Science:

• Comparative Anatomy
• Respiratory Physiology
• Equine Medicine

Background:

• Understanding the morphometric and functional characteristics of equine lungs is essential for diagnosing and treating respiratory diseases.
• Previous studies have provided limited detailed data on the structural components influencing gas exchange in horses.

Purpose of the Study:

• To conduct a detailed morphometric analysis of equine lung structure.
• To calculate the total pulmonary diffusion capacity for oxygen in horses.
• To investigate regional differences in lung morphology and their impact on gas exchange.

Main Methods:

• In situ glutaraldehyde fixation of equine lungs from two geldings (510 kg body weight, 38 L average lung volume).
• Morphometric analysis of stratified random samples from 22 lung regions using electron microscopy.
• Calculation of air space, interalveolar septa composition, surface areas, barrier thickness, and pulmonary diffusion capacity for oxygen.

Main Results:

• Gas exchange parenchyma constituted 86% of total lung volume (26.9 L air space, 5.6 L interalveolar septa).
• Average alveolar surface area was 2457 m², capillary surface area was 1663 m², and air-blood tissue barrier thickness was 1.37 µm.
• Total pulmonary diffusion capacity for oxygen ranged from 1.75 to 3.55 L/min x mmHg, with significant regional variations between apical and diaphragmatic lobes.

Conclusions:

• Equine lungs exhibit substantial regional heterogeneity in alveolar and capillary distribution, impacting gas exchange efficiency.
• The morphometric data provide a foundation for understanding normal equine respiratory function and pathological changes.
• Calculated diffusion capacity values offer critical insights into oxygen transport capabilities in the equine respiratory system.