Banzett R B, Butler J P, Nations C S, Barnas G M, Lehr J L, Jones J H
Harvard School of Public Health, Department of Environmental Science & Physiology, Boston, MA 02115.
Respir Physiol. 1987 Dec;70(3):287-300. doi: 10.1016/0034-5687(87)90011-9.
The non-reversing gas flow pattern in the avian lung has been attributed to 'aerodynamic valves'. A fundamental property of all aerodynamic valves is their dependence on inertial forces in the gas stream: sufficient reduction of inertial forces will cause aerodynamic valves to fail. If valving in the avian lung is aerodynamic, it should fail when gas stream momentum is reduced. We tested the dependence of the inspiratory valves in the goose lung on gas density and gas flow velocity. A bolus of tracer gas was placed in the tracheal cannula during an end-expiratory pause. Tracer gas appearance in a cranial air sac during the following inspiration and pause was used to deduce failure of the 'inspiratory valve' in cyclically ventilated geese. Little or no tracer entered the sac under control conditions, which approximated resting breathing, indicating highly effective valving. Lower flow rate or lower gas density caused increased tracer appearance, indicating valve failure. These results demonstrate the importance of gas inertial forces to normal valve function, and are direct evidence for the aerodynamic nature of the avian inspiratory valve.
鸟类肺部气体单向流动模式归因于“气动瓣膜”。所有气动瓣膜的一个基本特性是它们依赖气流中的惯性力：惯性力充分减小会导致气动瓣膜失效。如果鸟类肺部的瓣膜作用是气动的，那么当气流动量减小时它应该会失效。我们测试了鹅肺吸气瓣膜对气体密度和气流速度的依赖性。在呼气末暂停期间，将一团示踪气体置于气管插管中。利用接下来吸气和暂停期间示踪气体在头端气囊中的出现情况，来推断周期性通气的鹅中“吸气瓣膜”的失效情况。在接近静息呼吸的对照条件下，很少或没有示踪剂进入气囊，表明瓣膜作用非常有效。较低的流速或较低的气体密度会导致示踪剂出现增加，表明瓣膜失效。这些结果证明了气体惯性力对正常瓣膜功能的重要性，并且是鸟类吸气瓣膜具有气动性质的直接证据。
