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Have been dogunly busy lately, but to catch up on some of the recent tek questions: About the Dive Reflex question: The dive reflex does not function in humans as in marine mammals. The dive reflex does not seem to reduce your body's oxygen demands. In conscious humans, cold water immersion raises oxygen consumption due to the increased work of keeping warm. The dive reflex does not increase breath holding time in cold water. Cold immersion reduces it compared to non-immersion in neutral temperature. About the Blood Like Sea Water question: Your blood is not the same concentration as sea water either now or primordially. Sea water is about three times more concentrated than human blood. Even sea creatures have different osmolarities than the sea, and have different body challenges to maintain their accustomed levels. Some are higher, some lower. They have to constantly pump stuff in or out to keep their bodies within normal level. There's more - this is an interesting area of physiology - will have to wait for my schedule to quiet down. Come to Dive Philadelphia (shameless plug for the show) and we'll talk. About the Voice Change With Masks And Helium questions: Gasmaskyness is a big boost in one frequency range due to the resonant cavity of the mask. There was a good paper by the British Broadcasting Corp a few years ago on how to fix this problem (they weren't deep enough to require helium). Fixing it, according to sound engineering wizard David Josephson, is done by sampling speech through a normal microphone at the surface, looking at the frequency/amplitude distribution of a standard text, then doing the same through the mask/mic underwater, computing the difference between the two spectra and implementing a filter that had the inverse response. With helium, density of the breathing medium determines springiness of the vocal folds (cords) and so their vibrational frequency. With less dense air, pitch is higher. To unscramble helispeak you heterodyne the resulting frequency down to its normal range. There are speech-changing telephones that do this all on one chip. About the Haldane Question: Haldane is the name of a whole family of Scottish scientists and thinkers. J.S. Haldane, Scottish born British physiologist (1860-1936), co- developed the first scientific attempt to estimate amounts of inert gas absorbed and released by body tissues, now one of several methods. Many current decompression tables and computers are based on versions of the Haldane model. J.S. Haldane sometimes used his young son John Burdon Sanderson Haldane (1892-1964) as an experimental subject. J.B.S. Haldane grew up to be a geneticist, Marxist, and devotee of Hindu culture. No commentary here of what decompression studies can do to/for you. About the Perfluorcarbon question: Perfluorocarbons were used in experiments of liquid breathing since the 1960's. Dr. Tom Shaffer did the work used for the book The Abyss. He will speak about his liquid breathing work, and has neat slides (shameless plug for the Medicine & Physiology of Diving Symposium at Dive Philadelphia Sat. 15 Oct. Be there). Today his work continues with preemie babies whose lungs are incapable of breathing air. As far as I understand it, a perfluorocarbon called LiquiVent expands alveoli at low pressures allowing ventilation, and exchanges O2 for CO2. Come talk to him. Good Things, Dr. Jolie Bookspan
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