Hyperbaric tracheobronchial compression in cetaceans and pinnipeds

Area of Science:

• Marine biology
• Comparative physiology
• Biomechanics

Background:

• Understanding marine mammal diving physiology requires knowledge of airway compressibility at depth.
• Limited data exists on changes in cetacean and pinniped airway shape and volume under pressure.

Purpose of the Study:

• To quantify changes in marine mammal airway volume with increasing hydrostatic pressure.
• To investigate species-specific differences in airway compliance in pinnipeds and cetaceans.

Main Methods:

• Post-mortem computed tomography (CT) imaging of marine mammal airways (harbor seal, gray seal, harp seal, harbor porpoise, common dolphin) in a hyperbaric chamber.
• 3D volume reconstructions of trachea and bronchi segments under varying pressure treatments.
• Analysis of airway collapse dynamics and compliance at different lung inflation levels.

Main Results:

• All tested marine mammal airways showed significant volume reduction with increased pressure.
• Harbor seal and common dolphin airways approached complete collapse at the highest pressures.
• Common dolphin bronchi exhibited pressure-dependent compression dynamics influenced by lung inflation; harbor seal and gray seal trachea were less compliant than their bronchi.

Conclusions:

• Marine mammal airways are highly compressible, with significant species-specific variability.
• Airway collapse at depth may limit gas exchange and increase the risk of decompression sickness.
• Lung volume plays a critical role in maintaining airway patency during dives.