Moby-Sick: Sea mammals get the bends, too
Growing up, I heard “the bends” referenced in a non-Radiohead context several times, but the concept didn’t really hit me until I read Gary Smith’s phenomenal 2003 Sports Illustrated cover story, “The Deadly Dive.” It chronicles the tragic, obsessive free-diving couple Pipin Ferreras and Audrey Mestre, the latter of whom died while attempting to set a world record in 2002. (The article is unfortunately not online; James Cameron optioned the film rights in 2006, but the project appears to have stalled). The descriptions of decompression sickness (DCS) and N2 bubbles expanding in the bloodstream had me pressing back into the sofa cushion, sucking in air, queasy with tension. It also made me realize, bleakly, that no matter how good our technology gets, the human body is unequipped to deal with the crushing depths of the sea.
As it turns out, we’re not alone in that regard. A new study out this week from the Proceedings of the Royal Society B indicates, somewhat surprisingly, that deep-diving ocean mammals such as whales, seals, and dolphins may not be immune to the effects of DCS as had been previously assumed. A number of beached whales and dolphins have shown evidence of nitrogen bubbling in their bones, a telltale sign of rapid pressure change. Scientists had previously thought that these animals enjoyed biological mechanisms that mitigated or eliminated the effects of the bends. In fact, it seems that sea mammals simply tailor their behavior to avoid the stress whenever possible. Whales’ lungs actually collapse below a certain depth, which helps mitigate nitrogen build-up by equalizing the pressure (provided the animal takes a shallower angle upon ascending). In 2000, the Navy suggested that sonar emissions (which can be mistaken for a predator) might be causing whales and dolphins to adopt unsafe diving patterns. It’s likely that other emergencies would have a similar effect, weakening the animals over the long term.
This latest development suggests intriguing new avenues of study and opportunities for cross-species comparison. We’ve only recently gotten a grasp on the physical properties of the bends and why pre-formed N2 bubbles exist in human tissue at all. In 2007, a University of Houston scientist developed a laser-based imaging device that can be used to diagnose DCS immediately instead of waiting for patients to develop symptoms later on. The technology could potentially be adapted to monitor DCS symptoms in still-living mammals. A future longitudinal study might involve tagging a young whale, dolphin, or seal and then periodically checking it for signs of N2 bubbling to assess the effect over time.
Goldman, S. Free energy wells for small gas bubbles in soft deformable materials. The Journal of Chemical Physics, 2010; 132 (16): 164509 DOI: 10.1063/1.3394940
Hooker, SK, et al. Deadly diving? Physiological and behavioural management of decompression stress in diving mammals. Proceedings of the Royal Society B, 2011; published online before print December 21, 2011, doi:10.1098/rspb.2011.2088
“Laser Can Spot Illness Before Symptoms Appear.” University of Houston release November 12, 2007; http://www.uh.edu/uhtoday/archives/2007/november-2007/111207_laserscanspot.php