Department of Mechanical Engineering, McCormick School of Engineering, Northwestern University, Evanston, IL 60201.
Theoretical and Applied Mechanics Program, McCormick School of Engineering, Northwestern University, Evanston, IL 60201.
J Biomech Eng. 2024 Feb 1;146(2). doi: 10.1115/1.4064125.
Functional luminal imaging probe (FLIP) is used to measure cross-sectional area (CSA) and pressure at sphincters. It consists of a catheter surrounded by a fluid filled cylindrical bag, closed on both ends. Plotting the pressure-CSA hysteresis of a sphincter during a contraction cycle, which is available through FLIP testing, offers information on its functionality, and can provide diagnostic insights. However, limited work has been done to explain the mechanics of these pressure-CSA loops. This work presents a consolidated picture of pressure-CSA loops of different sphincters. Clinical data reveal that although sphincters have a similar purpose (controlling the flow of liquids and solids by opening and closing), two different pressure-CSA loop patterns emerge: negative slope loop (NSL) and positive slope loop (PSL). We show that the loop type is the result of an interplay between (or lack thereof) two mechanical modes: (i) neurogenic mediated relaxation of the sphincter muscle or pulling applied by external forces, and (ii) muscle contraction proximal to the sphincter which causes mechanical distention. We conclude that sphincters which only function through mechanism (i) exhibition NSL whereas sphincters which open as a result of both (i) and (ii) display a PSL. This work provides a fundamental mechanical understanding of human sphincters. This can be used to identify normal and abnormal phenotypes for the different sphincters and help in creating physiomarkers based on work calculation.
功能腔内腔成像探头（FLIP）用于测量括约肌的横截面积（CSA）和压力。它由一个被充满流体的圆柱形袋子包围的导管组成，两端封闭。通过 FLIP 测试绘制括约肌收缩周期中的压力-CSA 滞后图，可以提供有关其功能的信息，并提供诊断见解。然而，对于这些压力-CSA 环的力学特性，所做的工作有限。这项工作提供了不同括约肌的压力-CSA 环的综合描述。临床数据表明，尽管括约肌具有相似的功能（通过打开和关闭来控制液体和固体的流动），但会出现两种不同的压力-CSA 环模式：负斜率环（NSL）和正斜率环（PSL）。我们表明，环的类型是两种机械模式之间相互作用的结果（或缺乏相互作用）：（i）神经介导的括约肌松弛或外部施加的拉力，以及（ii）靠近括约肌的肌肉收缩，导致机械膨胀。我们得出的结论是，仅通过机制（i）发挥作用的括约肌表现出 NSL，而由于（i）和（ii）两者都起作用的括约肌则显示出 PSL。这项工作提供了对人类括约肌的基本机械理解。这可用于识别不同括约肌的正常和异常表型，并有助于基于工作计算创建生理标志物。
