Capturing the in situ behavior of airway smooth muscle in human bronchi using an ex vivo system that simulates breathing maneuvers

肺内呼吸道平滑肌(ASM)的生理功能尚不清楚。这种精细的结构存在于从气管到呼吸性细支气管的每一个呼吸道中，缺乏归属的功能令许多研究人员感到困惑。我们认为，这种困惑源于传统上用于研究ASM收缩的方法和技术。为了捕捉ASM的原位行为并破译其在呼吸力学中的作用，可能需要一种改进的体外环境来更准确地模拟ASM运行的体内条件。 ASM所部署的力量依赖于无数痉挛原(如乙酰胆碱)和支气管扩张剂(如一氧化氮)之间的平衡，这两者共同决定了ASM的激活水平。然而，ASM部署的力量不仅仅是其激活程度的函数。ASM运行的时间长度也对其产生力量的能力有很大影响。为了深入了解ASM在体内的生理功能，对ASM进行原位研究势在必行。 我们最近描述了如何在体外(器官浴内)原位研究ASM。我们证明ASM的原位长度与最优长度(即发生最大力的长度)相去甚远。然而，这些实验是在静态条件下进行的。尽管我们的发现代表了对ASM生物学的理解的重大进步，但我们的体外环境可以改进，以更紧密地模拟体内的条件。 ASM被调用在体内运行的长度不是静态的。肺是一个动态的器官，需要大量和持续的体积变化才能完成其呼吸功能。这些体积的变化使ASM的长度发生了振荡变化。因此，除了设置在原位长度之外，ASM还需要在模拟体内发生的肺体积变化的长度变化期间进行研究。该计划的目标是在体外重建ASM在体内运行的动态环境中，确定ASM在人体支气管力学中的作用。 这项研究计划旨在： 1-在ASM可在体内经历的一定长度范围内，确定在ASM动态和重复的延长和缩短周期中，不同ASM激活水平下人支气管ASM的长度-力关系。 2-确定在体内可以发生的速率范围内的长度变化率是否影响ASM的长度-力关系。 3-确定用于激活ASM的痉挛原的选择是否影响反应。 4-将这些实验数据拟合到计算模型中，以估计改变ASM激活和长度对ASM缩短、气道狭窄和不同大小的单个气道的气流阻力的影响。 该项目将确定人体支气管ASM在生理范围和长度变化率不同激活水平下产生的力的大小。它还将预测长度和ASM激活如何结合起来影响ASM缩短、气道狭窄和气流阻力。最终，它将决定所有这些因素如何相互作用，影响肺功能。我们认为，在动态系统中更好地描述ASM的长度-力关系是理解ASM生理功能的先决条件。该计划将为高素质人才(HQP)提供呼吸生理学、生物力学、组织生物学、药理学和计算模型分析方面的尖端专业知识。

The physiologic function of airway smooth muscle (ASM) within the lung is unknown. The lack of ascribed function of such an elaborated structure, which is present in every airway from the trachea to the respiratory bronchioles, perplexes a lot of investigators. We believe that this puzzlement arises from the methods and techniques that are traditionally used to study ASM contraction. An improved ex vivo setting that simulates more accurately the in vivo conditions in which ASM operates may be required to capture its in situ behavior and to decipher its role in the mechanics of breathing. The force deployed by ASM relies on a balance between a myriad of both spasmogen (e.g. acetylcholine) and bronchodilators (e.g. nitric oxide), which collectively determine the level of ASM activation. However, the force deployed by ASM is not only a function of its level of activation. The length at which ASM operates also significantly affects its capacity to generate force. To gain valuable insights into the physiologic function of ASM in vivo, it is thus imperative to study ASM at in situ length. We recently described how ASM can be studied at in situ length ex vivo (within an organ bath). We demonstrated that the in situ length of ASM is surprisingly far from the optimal length (i.e. the length at which maximal force occurs). However, these experiments were performed in static conditions. Although our findings represented significant advance to the understanding of ASM biology, our ex vivo setting can be improved to emulate in vivo conditions even more closely. The length at which ASM is called to operate in vivo is not static. The lung is a dynamic organ that requires substantial and continuous changes of volume to fulfill its ventilatory function. These changes of volume impose oscillatory changes in the length of ASM. Thus, in addition of being set at in situ length, ASM needs to be studied during changes of length that simulate the changes of lung volume that occur in vivo. The goal of this program is to determine the role of ASM in the mechanics of human bronchi within an ex vivo setting that recreates the dynamic environment in which ASM operates in vivo. This research program aims to: 1-Determine the length-force relationship of ASM in human bronchi at different levels of ASM activation during dynamic and repetitive cycles of lengthening and shortening within a range of lengths that ASM can experience in vivo. 2-Determine whether the rate of length change, within a range of rates that can occur in vivo, affects ASM length-force relationship. 3-Determine whether the choice of spasmogen used to activate ASM influences the response. 4-Fit these experimental data into a computational model to estimate the influence of changing ASM activation and length on ASM shortening, airway narrowing and resistance to airflow in individual airways of different sizes. This project will determine the amount of force generated by ASM of human bronchi at different levels of activation during physiological range and rate of length changes. It will also predict how length and ASM activation combine to affect ASM shortening, airway narrowing and resistance to airflow. Ultimately, it will determine how all these factors interact to affect lung function. We believe that a better characterization of the length-force relationship of ASM in a dynamic system that simulates the perpetual changes of lung volume that occur in vivo is a prerequisite to understand the physiologic function of ASM. This program will provide highly qualified personnel (HQP) with cutting edge expertise in respiratory physiology, biomechanics, tissue biology, pharmacology and computational modeling analyses.