Jones J H, Effmann E L, Schmidt-Nielsen K
Respir Physiol. 1981 Aug;45(2):121-31. doi: 10.1016/0034-5687(81)90054-2.
The complex pattern of air flow in the respiratory system of birds suggests that certain sites function as valves. To examine the possibility of mechanical valving, rather than aerodynamic valving, we recorded radiographic images of the orifices where the medioventral secondary bronchi branch from the primary bronchus in resting Pekin ducks. Analysis of the images indicated that the orifices do not change size or shape during the respiratory cycle, suggesting that they function as aerodynamic rather than mechanical valves in directing air flow through the lung.
鸟类呼吸系统中复杂的气流模式表明某些部位起到了瓣膜的作用。为了研究机械瓣膜而非气动瓣膜的可能性，我们记录了静息状态下北京鸭初级支气管中腹侧次级支气管分支处孔口的X光图像。图像分析表明，这些孔口在呼吸周期中大小和形状均未改变，这表明它们在引导气流通过肺部时起到的是气动瓣膜而非机械瓣膜的作用。
