Banzett R B, Nations C S, Wang N, Fredberg J J, Butler J P
Respiratory Biology Program, Harvard School of Public Health, Boston, Massachusetts 02115.
Respir Physiol. 1991 Jun;84(3):295-309. doi: 10.1016/0034-5687(91)90125-3.
Inspiratory airflow in the avian lung completely bypasses the most cranial secondary bronchi (the ventrobronchi), and instead enters bronchi arising more caudally (the dorsobronchi). Dotterweich (1936) proposed that 'aerodynamic valves' prevented entry into the ventrobronchi. We have recently provided evidence that inspiratory aerodynamic valving in avian lungs depends on convective inertia in the primary bronchus (Banzett et al., 1987). Theoretical and physical models (Butler et al., 1988; Wang et al., 1988) showed that convective inertia could effect valving, but the effectiveness of valving at resting flows was less than that observed in the bird. This leads us to hypothesize that a segment of the primary bronchus is constricted, accelerating the gas and enhancing the convective inertia. To test this hypothesis in the present work we measured pressures throughout the airways and air sacs in anesthetized, pump-ventilated geese at different flow rates and gas densities. Our data show: (1) there is a large pressure drop in the primary bronchus close to the ventrobronchial junction, indicating the presence of a constriction; (2) this pressure drop increases with gas density and flow; (3) the convective inertia at this site is more than 10 times downstream opposing pressures. We conclude that the primary bronchus just cranial to the first ventrobronchus forms a constriction which accelerates inspired air. Furthermore, we conclude that the convective inertia of gas leaving this segment is sufficient to achieve inspiratory valving.
鸟类肺部的吸气气流完全绕过最靠前的次级支气管（腹支气管），而是进入更靠后的支气管（背支气管）。多特魏希（1936年）提出，“气动瓣膜”阻止气流进入腹支气管。我们最近提供的证据表明，鸟类肺部的吸气气动瓣膜作用取决于初级支气管中的对流惯性（班泽特等人，1987年）。理论和物理模型（巴特勒等人，1988年；王等人，1988年）表明，对流惯性可产生瓣膜作用，但在静息气流下瓣膜作用的效果低于在鸟类中观察到的效果。这使我们推测，初级支气管的一段会变窄，加速气体流动并增强对流惯性。为了在本研究中验证这一假设，我们在不同流速和气体密度下，对麻醉后经泵通气的鹅的整个气道和气囊中的压力进行了测量。我们的数据显示：（1）在靠近腹支气管连接处的初级支气管中有很大的压降，表明存在狭窄；（2）该压降随气体密度和流速增加；（3）该部位的对流惯性比下游的反向压力大10倍以上。我们得出结论，第一个腹支气管前方的初级支气管形成一个狭窄部位，可加速吸入的空气。此外，我们得出结论，离开该段的气体的对流惯性足以实现吸气瓣膜作用。
