Why Don’t Whales Get “The Bends” ?
Scuba divers are quite familiar with the dangers associated with decompression. Diving deep into high-pressure waters forces the compressed air in their tanks into solution in the blood stream. As they surface, some of the nitrogen in this dissolved air emerges as bubbles of nitrogen gas, which is highly damaging to blood vessels, and can be lethal. This is known commonly as “the bends”, and medically as decompression syndrome. Thus, divers know that they must resurface at a slow rate to give the body time to dispense with the nitrogen. Even with this precaution, many divers experience pain and even bone damage (known as osteonecrosis) from repeated diving over many years.
Scientists who study Cetacea (the group that includes whales, porpoises and dolphins) have long puzzled over how deep-diving whales (which are also air-breathing mammals like us) avoid this dangerous, decompression condition, that is, why don’t whales get the bends?
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As it turns out they do, or rather, they used to–millions of years ago. A study of fossil Cetacea bones (Beatty, Rothchild 2008) show indications of osteonecrosis, suggesting that some species of whale did indeed suffer from deep-diving induced bone damage. The researchers suggest that the evolution of physiologic mechanisms to thwart this syndrome occurred relatively rapidly, as it would be under strong selective pressure to do so.
Perhaps some of these early Cetacea develop a circulatory system and/or or blood clearing mechanism that expediently and safely removed the nitrogen coming out of solution in the blood. Human blood cells use hemoglobin, a specialized protein, to trap oxygen and transport it to tissues. Whales have a different protein for this known as myoglobin. There may be some additional purpose or function to this protein besides oxygen transport. But it may be something entirely different, like a sequence of genes that code for nitrogen transport, or block nitrogen from decompressing in the blood.
So, the actual physiologic mechanism that prevents decompression syndrome in the modern whale remains a bona fide mystery of the animal world, awaiting some future solution. The answer to this mystery may prove valuable to human deep sea exploration, which many feel is still the last frontier of discovery on Earth. Less than 10% of the planet’s oceans and seas have been mapped or explored.
photo: Pacman for NOAA (public domain)
Thank you. A fascinating subject to find on this site highlighting how these animals have evolved in their environment. A nice complement to the publication’s concern with our relationship to nature and how best to understand and respect it.