Griffiths D J
Department of Applied Sciences in Medicine, University of Alberta, Edmonton, Canada.
J Biomech Eng. 1989 Aug;111(3):206-11. doi: 10.1115/1.3168367.
In steady flow through nonuniform collapsible tubes a key concept is the compressive zone, at which flow limitation can occur at both high and low Reynolds numbers. Ureteral peristalsis can be considered as a series of compressive zones, corresponding to waves of active muscular contraction, that move at near-constant speed along the ureter towards the bladder. One-dimensional, lubrication-theory analysis shows that peristalsis can pump urine from kidney into the bladder only at relatively low mean rates of urine flow. Under these circumstances isolated boluses of urine are propelled steadily through the ureter (assumed uniform) by the contraction waves. At higher mean rates of flow the behavior depends on whether the frequency of peristalsis is higher or lower than a critical value. For frequencies above the critical value steady propagation of boluses that are in contact with contraction waves at both ends is possible. As the flow rate rises the urine begins to leak through the contraction waves and steady peristaltic flow breaks down. There is an upper limit to the mean flow rate that can be carried by steady peristalsis, which depends on the mechanical properties of the ureter. At high flow rates the peristaltic contractions do not pump but hinder the flow of urine through the ureter.
在通过非均匀可塌陷管道的稳定流动中，一个关键概念是压缩区，在该区域，无论雷诺数高低，都可能出现流动受限的情况。输尿管蠕动可被视为一系列压缩区，它们对应于活跃的肌肉收缩波，以近乎恒定的速度沿输尿管向膀胱移动。一维润滑理论分析表明，蠕动仅在相对较低的平均尿流速率下才能将尿液从肾脏泵入膀胱。在这种情况下，孤立的尿团会被收缩波稳定地推动通过输尿管（假设为均匀的）。在较高的平均流速下，其行为取决于蠕动频率是高于还是低于临界值。对于高于临界值的频率，两端与收缩波接触的尿团有可能稳定传播。随着流速增加，尿液开始从收缩波中泄漏，稳定的蠕动流瓦解。稳定蠕动所能承载的平均流速存在上限，这取决于输尿管的力学特性。在高流速下，蠕动收缩不会推动尿液，反而会阻碍尿液通过输尿管的流动。
