人在深度潜水后如果回升水面速度过快，会出现恶心、身体疼痛等不适，而海象、海狮等海洋哺乳动物却能在深水中自如升降，美国的一项新研究揭示了其中原因。
从深水迅速上浮时，人体会因气压迅速下降而在血液中形成氮气泡，导致身体机能失调，医学上称为气泡栓塞病。美国斯克里普斯海洋研究所的科研人员在新一期英国期刊《生物学通讯》上报告说，他们通过长时间追踪研究一头海狮发现，这种哺乳动物之所以能在深达数百米的水中上下自如游动，得益于一种主动进行“肺萎陷”的本领。
研究人员捕获这头雌性成年海狮后，在其身体上安装了一枚小型记录器，用以实时监测海狮体内气压、下潜深度等一系列数据。此后，研究人员将海狮放归大海，并跟踪研究其48次下潜捕食的情况。
研究发现，在潜至约225米深时，海狮体内的气压骤降，这意味着它主动实施“肺萎陷”，将附着在支气管上的大量肺泡压缩，使整个肺部体积缩小。这相当于关闭了向血管输送气体成分的“开关”，保证氮气等无法进入血液，避免其对身体机能的侵扰。肺部关闭后，海狮会通过其大量的支气管和气管中储存的氧维持身体机能运转。（生物谷Bioon.com）
doi: 10.1098/rsbl.2012.0743
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Lung collapse in the diving sea lion: hold the nitrogen and save the oxygen
Birgitte I. McDonald* and Paul J. Ponganis
Lung collapse is considered the primary mechanism that limits nitrogen absorption and decreases the risk of decompression sickness in deep-diving marine mammals. Continuous arterial partial pressure of oxygen profiles in a free-diving female California sea lion (Zalophus californianus) revealed that (i) depth of lung collapse was near 225 m as evidenced by abrupt changes in during descent and ascent, (ii) depth of lung collapse was positively related to maximum dive depth, suggesting that the sea lion increased inhaled air volume in deeper dives and (iii) lung collapse at depth preserved a pulmonary oxygen reservoir that supplemented blood oxygen during ascent so that mean end-of-dive arterial was 74 ± 17 mmHg (greater than 85% haemoglobin saturation). Such information is critical to the understanding and the modelling of both nitrogen and oxygen transport in diving marine mammals.
