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Message: <blockquote data-quote="Steverooo" data-source="post: 1162527" data-attributes="member: 9410">HERE's why WE can't (Yee-OWwch)!This is from the PBS site: <a href="http://www.pbs.org/odyssey/odyssey/...transcript.html" target="_blank">http://www.pbs.org/odyssey/odyssey/...transcript.html</a>Because they spend almost 80% of their lives at depth, the amount of time we see sperm whales at the surface is comparatively low. As a result, we spend the majority of our time tracking sperm whales by homing in on their sounds. While the dives of adult females tend to last around 45 minutes mathotoure males are capable of staying beneath the surface for more than 90 minutes. Male sperm whales can also dive to astonishing depths. They have been found entangled in submarine telephone cables at depths of 1,000 meters, while a study in the Caribbean Sea using acoustic transponders and sonar revealed whales diving to depths of 1,185 meters and another was possibly to 2,000 meters. (The Smithsonian Answer Book. James Mead & Joy Gold) People often ask us how these air breathing mammals can dive to such great depths for extended periods of time without suffering from decompression sickness, also known as the 'bends.' The 'bends' is a condition suffered by people when they breathe air under pressure and ascend to the surface too fast (for example, when scuba diving). As humans dive deeper, they continue to breathe air at increasing pressure where more nitrogen gets driven by that pressure into the blood stream. Upon a sudden return to the normal atmosphere - i.e., upon surfacing too fast, the nitrogen that has saturated the blood, comes rapidly out of solution and forms bubbles. These bubbles accumulate in joints, in the blood, the brain and other parts of the nervous system, resulting in a blockage which reduces the oxygenated blood supply-something that is usually severely painful and can cause death. To avoid the 'bends', a human diver must return to the surface slowly, stopping at specific depths to breathe for specific times in order to allow the body time to readjust, and for any nitrogen bubbles to dissipate. Whales are not subject to the 'bends' because they don't breathe air under pressure the way a human SCUBA diver does when diving. Whales breathe at the surface only, then hold their breath and dive. It seems likely that they don't carry enough air down to have the 79% of it that is nitrogen cause them problems. And because they are able to avoid too much excess nitrogen in the blood, they don't get the 'bends'. Because atmospheric pressure doubles every 10 meters, a whale at a depth of 500 meters experiences a pressure about fifty times greater than atmospheric pressure at the surface. Once it has dived to about 200 meters - the whale has far exceeded the depth at which humans can breathe air and still function properly. The air the whale dove with has been compressed to 25% of its original volume and the lungs and jointed rib cage have collapsed completely. The heart rate has dropped dramatically and non-essential processes have been much diminished because freshly oxygenated blood supply to peripheral regions has been cut off. Because of the compression and collapse of the cavities where gas-exchange takes place, air is excluded from most of the respiratory surface of the lungs, meaning that no gas exchange can occur between the blood and air in the lungs. This prevents absorption of the nitrogen that might otherwise pass into the blood and lead to the bends when the whale surfaces for its next breath.</blockquote>

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