Pulmonary ventilation-perfusion mismatch: a novel hypothesis for how diving vertebrates may avoid the bends

Area of Science:

• Marine vertebrate diving physiology
• Gas exchange dynamics
• Decompression sickness (DCS) mechanisms

Background:

• Traditional theory posits hydrostatic lung compression prevents nitrogen (N₂) uptake and gas emboli (GE) in diving marine mammals.
• Evidence from stranded cetaceans and sea turtles suggests GE and DCS symptoms can occur, challenging existing models.
• Theoretical modeling indicates current understanding of diving physiology is insufficient, predicting high DCS risk in natural dive profiles.

Purpose of the Study:

• To propose alternative mechanisms for gas exchange control in marine vertebrates during dives.
• To explain how marine animals avoid diving-related decompression issues.
• To investigate the role of ventilation-perfusion mismatch in N₂ uptake and GE risk.

Main Methods:

• Review and synthesis of published data from marine mammals and sea turtles.
• Theoretical modeling of tissue and blood gas dynamics in breath-hold divers.
• Analysis of ventilation ([Formula: see text]) and perfusion ([Formula: see text]) distribution in the lung.

Main Results:

• Marine vertebrates may control N₂ uptake by managing regional alveolar ventilation and lung perfusion ([Formula: see text] mismatch).
• Stressful anthropogenic disturbances (e.g., sonar) can alter this [Formula: see text] mismatch, elevating N₂ uptake and GE risk.
• This proposed mechanism offers a new explanation for GE occurrence and avoidance strategies in air-breathing marine vertebrates.

Conclusions:

• Diving marine vertebrates likely employ sophisticated gas exchange regulation beyond simple lung collapse.
• Disruption of ventilation-perfusion matching is a plausible cause of gas emboli in marine animals.
• This research opens new avenues for understanding marine mammal diving physiology and the impacts of anthropogenic noise.