Lung mechanical properties in the West Indian Manatee (Trichechus manatus)

Airway dimensions, extent of cartilage reinforcements and lung mechanical properties were examined in excised lungs of the West Indian Manatee (Trichechus manatus). All airways with a mean inside diameter of more than 0.6 mm had complete cartilaginous rings in their walls, and cartilage reinforcement extended into the respiratory bronchi. Expiratory flow rates over the vital capacity range were higher than those encountered in humans varying between 20 and 50% of peak flow at 25% of vital capacity. They were, however, lower than in other marine mammals. The ratio of lung compliance to lung weight was found to be 0.67 ml/(g · cm H₂O) compared to 0.18 ml/(g · cm H₂O) in terrestrial mammals. This together with a high gas-tissue ratio of 11 mg/g for the inflated manatee lung indicates that strong airway reinforcements are necessary to prevent airway collapse during exhalation.