Scheid P
Respir Physiol. 1978 Jan;32(1):27-49. doi: 10.1016/0034-5687(78)90098-1.
A number of models is analyzed to study gas exchange between blood capillaries and air capillaries in the avian parabronchial wall when diffusion is the only transport mechanism in the air capillaries. The existing anatomical arrangement of blood capillaries that traverse the periparabronchial tissue from peripherally located arterioles to draining venules at the luminal surface appears to provide a particularly high gas exchange efficiency. Application of the theory to measurements in the hen using histological estimates suggests that substantial concentration gradients exist inside the air capillary gas whose magnitude vary along the parabronchus. Thus at the gas inflow end of the parabronchus the partial pressure drop within the air capillaries could amount, for both O2 and CO2, to about 10--15 torr at rest and to 30--40 torr during exercise. Due to the peculiar arrangement of capillary blood flow to the air capillaries the effects of these gradients on gas exchange are very slight during rest. During exercise, however, the diffusional resistance inside the air capillaries may become limiting for the over-all gas exchange, and other mechanisms may be needed to secure respiratory gas transfer.
当扩散是气体微气管中唯一的传输机制时，分析了若干模型以研究鸟类副支气管壁中血液微气管与气体微气管之间的气体交换。现有的血液微气管解剖结构是从外周的小动脉穿过支气管周围组织到管腔表面的引流小静脉，这种结构似乎具有特别高的气体交换效率。将该理论应用于对母鸡的测量，利用组织学估计表明，气体微气管内存在显著的浓度梯度，其大小沿副支气管变化。因此，在副支气管的气体流入端，气体微气管内的氧分压和二氧化碳分压下降，在休息时约为10-15托，运动时为30-40托。由于流向气体微气管的毛细血管血流的特殊排列，这些梯度对气体交换的影响在休息时非常轻微。然而，在运动期间，气体微气管内的扩散阻力可能会限制整体气体交换，可能需要其他机制来确保呼吸气体的传输。
