Whales that dive deep and other marine mammals can get curves, the same painful and life-threatening decompression sickness that affects divers that emerge too quickly. A new study offers a hypothesis of how marine mammals generally avoid curves and how they can succumb under stress conditions.
The key is the unusual lung architecture of whales, dolphins and porpoises (and possibly other diving vertebrates that hold their breath), which creates two different lung regions under pressure at sea, according to researchers at the Woods Hole Oceanographic Institution ( WHOI) and the Oceanographic Foundation in Spain. His study was published on April 25, 2018 in the journal Proceedings of the Royal Society B .
"How many marine mammals and turtles can dive so many times as deep as they do has perplexed scientists for a very long time," says Michael Moore, director of the Marine Mammal Center at WHOI and co-author of the study. "This document opens a window through which we can take a new perspective on the issue."
When mammals breathing air are submerged at high-pressure depths, their lungs are compressed. It collapses its alveoli, the small sacs at the end of the airways where gas exchange occurs. Nitrogen bubbles accumulate in the bloodstream and tissue of animals. If they rise slowly, nitrogen can return to the lungs and exhale. But if they rise too fast, the nitrogen bubbles do not have time to spread again to the lungs. Under less pressure at shallower depths, nitrogen bubbles expand in the bloodstream and tissues, causing pain and damage.
The structure of the breast of marine mammals allows their lungs to compress. Scientists have assumed that this passive compression was the main adaptation of marine mammals to avoid taking excessive nitrogen in depth and obtain the curves.
In their study, the researchers took CT images of a dolphin, seal and a pressurized domestic pig in a hyperbaric chamber. The team was able to see how the pulmonary architecture of marine mammals creates two lung regions: one full of air and the other another collapsed. Researchers believe that blood flows mainly through the collapsed region of the lungs. This causes what is called a mismatch between ventilation and perfusion, which allows oxygen and carbon dioxide to be absorbed into the animal's bloodstream, while minimizing or preventing the exchange of nitrogen. This is possible because each gas has a different solubility in the blood. The terrestrial pig did not show that structural adaptation.
This mechanism would protect the cetaceans from absorbing excessive amounts of nitrogen and therefore minimize the risk of curves, says lead author Daniel García-Parraga of the Oceanografic Foundation.
However, he said, "excessive stress, as can occur during exposure to man-made sound, can cause the system to fail and increase blood flow to the air-filled regions." This would improve the exchange of gases and nitrogen increase blood and tissues as the pressure decreases during ascent. "
Scientists thought that marine mammals were immune to decompression, but an event of strandings in 2002 linked to the Navy's sonar exercises revealed that 14 whales died after the Canary Islands had gas bubbles in their tissues, A sign of the curves. The researchers say that the findings of the article could support the previous implications of decompression sickness in some cetacean strandings associated with marine sonar exercises.
The team says that further research will require the development of tools to analyze how lung ventilation and pulmonary blood flow patterns change stressors during diving.
A study examines how marine mammal diving handles decompression
Ventilation-perfusion pulmonary mismatch: a new hypothesis on how vertebrate divers can avoid curves, Procedures of the Royal Society B rspb.royalsocietypublishing.or … .1098 / rspb.2018.0482