Why deep-diving whales don't suffer from the bends
In short: Human divers face life-threatening nitrogen bubbles when surfacing too quickly. Yet, whales and dolphins descend to incredible depths for long periods without issue. Is it a biological superpower, or is their immunity actually a fragile physiological balance that can be broken?
Decompression sickness, commonly known as "the bends," occurs when soluble gases like nitrogen are absorbed into body tissues under high pressure. For humans using compressed gas tanks, these gases can form dangerous bubbles during ascent. While marine mammals do not breathe compressed gases while diving, they are not entirely immune to the condition.
A study published April 25, 2018, in Proceedings of the Royal Society B, suggests that the secret lies in unique lung architecture. Researchers from the Woods Hole Oceanographic Institution and Fundacion Oceanografic used CT images of a dolphin, seal, and domestic pig in a hyperbaric chamber to observe how lungs react to pressure. They found that in whales, dolphins, and porpoises, high pressure causes the alveoli—the tiny sacs where gas exchange occurs—to collapse, creating two distinct pulmonary regions.
The researchers believe blood flows primarily through the collapsed region. This creates a "ventilation-perfusion mismatch," allowing the animal to absorb oxygen and carbon dioxide while minimizing nitrogen exchange. Unlike the terrestrial pig, these marine mammals use this structural adaptation to prevent nitrogen buildup.
However, this defense mechanism is vulnerable. Lead author Daniel García-Parraga notes that extreme stress, such as exposure to human-made sound, can cause blood to flow into the air-filled regions. This increases nitrogen exchange, potentially leading to the bends. Evidence of this vulnerability was seen in a 2002 event where 14 whales stranded near the Canary Islands following navy sonar exercises were found to have gas bubbles in their tissues.
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Sources
- Summary by Intellect · source: Why Don't Marine Animals Get "The Bends"?
- Also: Last Word: Why don’t marine mammals like whales get ‘the bends’? | New Scientist
- Also: How do marine mammals avoid the bends? | Woods Hole Oceanographic Institution
- Also: How do marine mammals avoid the bends?
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