On how whales avoid decompression sickness and why they sometimes strand

Abstract

SUMMARYWhales are unique in that the supply of blood to the brain is not by the internal carotid arteries, but by way of thoracic and intravertebral arterial retia. We found in the harbor porpoise (Phocoena phocoena) that these retia split up into smaller anastomosing vessels and thin-walled sinusoid structures that are embedded in fat. The solubility of nitrogen is at least six times larger in fat than in water, and we suggest that nitrogen in supersaturated blood will be absorbed in the fat, by diffusion, during the very slow passage of the blood through the arterial retia. Formation of nitrogen bubbles that may reach the brain is thereby avoided. We also suggest that mass stranding of whales may be due to disturbances to their normal dive profiles, resulting in extra release of nitrogen that may overburden the nitrogen 'trap' and allow bubbles to reach the brain and cause abnormal behavior.

Respiratory function and mechanics in pinnipeds and cetaceans

“…An arterial rete has limited ability to expand, and its tortuosity and interconnections may trap bubbles or emboli and guarantee alternative flow pathways (collateral circulation) to prevent neural emboli and possible trauma (Vogl and Fisher, 1982;Blix et al, 2013). By contrast, the venous rete, being far more distensible, can engorge with blood and reduce the volume of gas-filled spaces, thereby protecting against lung squeeze [similar to the thoracic blood pooling reported in human breath-hold divers (Harrison and Tomlinson, 1956;Murdaugh et al, 1962;Craig, 1968;Hui, 1975;Ridgway et al, 1984)].…”

How Do Marine Mammals Manage and Usually Avoid Gas Emboli Formation and Gas Embolic Pathology? Critical Clues From Studies of Wild Dolphins

“…One example is the thoracic and vertebral arterial retia mirabilia that is present in several diving species, e.g., bottlenose dolphin, narwhal (Monodon monoceros), sperm whale (Physeter macrocephalus), beluga (Delphinapterus leucas), and harbor porpoise (Vogl and Fisher, 1982;Melnikov, 1997). These highly tortuous vascular deltas are embedded in adipose tissue and may provide a protective structure that traps and dissolves microbubbles before reaching the brain (Blix et al, 2013). However, it is not only the direct effect of bubbles that may cause symptoms, but symptoms may also be due to secondary effects in response to invading bubbles.…”

“…Following this, several analyses have attempted to determine the potential causes for these stranding events, which appeared to happen in close temporal and spatial proximity to naval sonar exercises (Cox et al, 2006;Hooker et al, 2012;Bernaldo de Quirós et al, 2019). Among the main working hypotheses were that changes in dive behavior or physiology (e.g., increased dive duration, activity, or ascent rate), or changes in cardiac output, would have resulted in increased N 2 uptake, which resulted in the formation of blood and tissue gas bubbles (Cox et al, 2006;Hooker et al, 2012;Blix et al, 2013;Fahlman et al, 2014b;Bernaldo de Quirós et al, 2019). As it is neither desirable nor ethically, legally, or logistically possible to perform controlled studies where marine mammals are exposed to decompression sequences that result in severe trauma, stress, or death, we therefore refer to the symptoms seen in breath-hold diving marine vertebrates as gas embolic pathology (GEP) to distinguish this from symptoms of DCS observed in humans.…”

De invloed van geluidspollutie op zeezoogdieren

“…Walvissen hebben longen en zijn dus gevoelig voor deze aandoening. Opnieuw heeft de evolutie een aantal ingenieuze aanpassingen voorzien waardoor walvissen kunnen duiken met een relatief laag risico op deze pathologie, onder meer door de vorming van uitgebreide bloedvatnetwerken (wondernetten of retia mirabilia) die de bloedvoorziening naar de vitale organen garanderen (Blix et al, 2013). Verder kunnen walvislongen collaberen op grotere dieptes.…”