How do whales cope with decompression sickness?

The structure of the chest of marine mammals is such that it allows their lungs to contract. This passive compression is a primary adaptation of marine mammals: it avoids excessive nitrogen levels in the blood when they are at depth. In the lungs of marine mammals, two sections are formed: one is filled with air, and the other is "compressed". Blood flows mainly through the second area - the one in which there is almost no air. This causes the so-called uneven ventilation and perfusion of different parts of the lungs, which allows oxygen and carbon dioxide to be absorbed in the animal's blood, while minimizing or preventing nitrogen exchange. This is possible because each gas has a different solubility in the blood. However, this natural mechanism can malfunction. For example, due to exposure to excessive noise that a person produces - on a ship, during research, prospecting, industrial work. A system failure leads to increased blood flow to the air-filled lung compartment. This promotes the expansion of gas exchange: the amount of nitrogen increases in blood and tissues when the pressure drops during ascent. Deep sea mammals may still be susceptible to decompression sickness - but not by nature.

First of all, I would like to dispel the misconception that marine mammals (dolphins, whales, seals, etc.) do not suffer from decompression sickness: due to their physiological characteristics, they are less susceptible to it, however, the cases of finding them on the shore with characteristic consequences of decompression sickness known, and even described in scientific articles (royalsocietypublishing.org and co.uk)

Now about the reasons why they are less susceptible to it:

Firstly, all vertebrates when immersed have general signs, expressed in varying degrees: a slowdown in the heart rate (brachycardia), a decrease in blood flow to the muscles (peripheral vasoconstriction). In marine animals, a reduced lung volume is added to this (namely, reduced, since this avoids saturation of the blood with nitrogen). This is also due to the special technique of deep diving of these mammals: being on the surface, they actively ventilate their lungs, saturating their muscles and blood with oxygen, and completely exhale air from their lungs before diving. Thus, at a depth in the lungs there is no nitrogen and, accordingly, there is no entry into the blood.

In whales, the air in their lungs under pressure is forced into the trachea, protected from external pressure and having a significant volume that does not allow air shrink. There is also speculation that whales are protected by their circulatory system, which consists of a network of arteries that occupy most of the animal's chest and supply blood to the whale's brain. Scientists have found that small network vessels pass through adipose tissue. At the same time, the blood flow rate in the vascular network (due to the large total cross-sectional area of ​​the vessels) is very low, due to which nitrogen from the blood diffuses through the walls of the vessels into the adipose tissue, and in fat, nitrogen is six times more soluble than in water. Scientists believe that this prevents the formation of nitrogen bubbles in the blood in cetaceans (article: biologists.org)

And in whales, it is simply impossible. The fact is that decompression sickness in people (divers) is associated with inhalation of high pressure air - as a result, neutral gases accumulate in the blood (most often nitrogen; but there may be helium and something else that is used in mixtures) as well with increased pressure - it is these gases that boil at a rapid rise. And the whale breathes atmospheric air with normal pressure - inhaled and dived; then he emerged and exhaled - and there was nowhere to get decompression sickness. Roughly the same thing happens with free-divers - athletes who dive to super-depths without breathing apparatus - they have nowhere to get any decompression sickness.