Pushing the Envelope of Hypoxemia: Blood Oxygen Depletion in Elephant Seals

海象是海豹和海狮中最优秀的潜水者；它通常会在潜水深度超过400米时屏住呼吸20分钟。这个项目研究的是让这只海豹能够做出如此出色潜水的生理机能。特别是，据推测，这些海豹可以承受极低的氧气水平，这使得它们在潜水时几乎完全耗尽血液中的氧气。这种对低氧水平的极端耐受性是任何哺乳动物都无法做到的，也远低于人类在不补充氧气的情况下攀登珠穆朗玛峰时的氧气水平。为了检验这一假设，海豹将配备背包氧气记录仪，在海豹潜水时提供血液中的氧气压力概况。预计在潜水结束时，血液中的含氧量将接近于零，正是这种几乎完全利用血氧的情况，使得海象能够像它们一样出色地潜水。这项研究将确定这些海豹推动自己的生理极限。这关系到它们在水下成功找到猎物的能力，也关系到它们在一个可能因过度捕捞和全球变暖而发生变化的环境中的整体生态。此外，海豹耐受如此低氧水平的机制可能与我们对人体组织暴露于缺氧或血流不足（低氧血症或缺血）的各种病理状态的理解和治疗有关。最后，除了让学生直接参与研究外，这个项目还将开发一个教育网站，提供深海鲸鱼、海豹、企鹅和海龟的行为和生理信息。

The elephant seal is the premier diver among seals and sea lions; it routinely holds its breath for 20 minutes as it dives to depths greater than 400 meters. This project investigates the physiology that allows this seal to make such remarkable dives. In particular, it is hypothesized that these seals can withstand extremely low levels of oxygen, and that this allows them to almost completely deplete their blood of oxygen during diving. Such extreme tolerance to low levels of oxygen is beyond that found in any mammal, and well below the oxygen levels found in humans attempting to climb Mt Everest without supplemental oxygen. In order to examine this hypothesis, seals will be equipped with backpack oxygen recorders which will provide a profile of the oxygen pressure in the blood as the seal dives. It is expected that the oxygen levels in the blood will be near zero by the end of the dive, and that it is this nearly complete utilization of the blood oxygen which allows elephant seals to dive as well as they do. This study will establish the physiological limits to which these seals push themselves. This is relevant to their ability to successfully find prey underwater and to their overall ecology in an environment that may be changing due to over fishing and global warming. In addition, the mechanisms which allow the seals to tolerate such low oxygen levels may be relevant to our understanding and treatment of various pathological states in humans in which tissues are exposed to inadequate oxygen or blood flow (hypoxemia or ischemia). Lastly, in addition to involving students directly in the research, this project will develop an educational website which will provide behavioral and physiological information on deep-diving whales, seals, penguins, and sea turtles.