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Been watching this Whales-and-bends thread. I don't know a whole lot about whales (Damnit Jim, I'm an ichthyologist, not a doctor!), but I did take a course on diving physiology which included a section on marine mammals, and I've seen a couple of talks by visiting researchers. I have some literature somewhere lost in my reprint heaps which I could try to dig out if anyone is *really* interested. Here's what I think I know: The majority of research on diving mammal physiology has examined issues of oxygen budget and metabolism, rather than avoidance of DCI. However, certain species are known to achieve incredible depths (something like 300 meters for Northern Elephant Seals, and on the order of 1000 meters [!!!] for Sperm Whales). You'd think that even breath-hold bounce dives to such depths would lead to DCI.... As Anthony mentioned, whales do have special conglomerations of blood vessels called retia mirabilia (spelling changes according to which textbook you look at) that pool blood in the core of the body. I don't think these serve to trap bubbles, however. Like I said, most research has been focused on why whales and other diving mammals can stay underwater so *long*, rather than why they can go so deep without getting bent. My understanding is that the going hypothesis on the latter question involves alterations of blood circulation patterns so that lung gas is not distributed to the majority of tissues during the course of the dive. During a dive, heart rate goes way down and blood is concentrated in the vital organs and is not circulated among less vital tissues. Also, I *think* that most of the oxygen metabolized during a dive is already in the circulatory system....in other words, blood is not needed to transport oxygen from the lungs to the tissues during the course of the dive. As Bridget already noted, seals (and I believe dolphins...I'm not certain about whales either) *exhale* prior to a dive. The offshoot of this (as Bridget already explained) is that pressurized nitrogen is also not distributed to the rest of the body, so the blood and tissues are never exposed to dissolved N2 at much greater pressures than 1 ATA. The reason why humans can't do the same dives is basically because their circulatory system is not designed optimally for breath-hold diving. The majority of oxygen in a human body at any given time is in the lungs (people can hold their breath as long as they can because blood continues to extract oxygen from alveoli during breath-hold). However, the majority of oxygen in diving mammals is distributed in the blood and tissues (particularly muscles). Please let me know if anyone wants me to dig up some references on this stuff. Aloha, Rich deepreef@bi*.bi*.ha*.or*
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