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

肺内气道平滑肌（ASM）的生理功能尚不清楚。这种复杂的结构存在于从气管到呼吸细支气管的每一个气道中，但缺乏归因于它的功能，这使许多研究者感到困惑。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。可能需要一种改进的离体环境，更准确地模拟ASM在体内的操作条件，以捕获其在原位的行为并破译其在呼吸机制中的作用。** ASM部署的力依赖于无数痉挛素（如乙酰胆碱）和支气管扩张剂（如一氧化氮）之间的平衡，它们共同决定ASM激活水平。然而，ASM部署的力量不仅仅是其激活水平的函数。ASM运行的长度也显著影响其产生力的能力。为了深入了解ASM在体内的生理功能，有必要对ASM进行原位长度的研究。**我们最近描述了如何在离体（器官浴内）原位研究ASM。我们证明，ASM的原位长度与最佳长度（即发生最大力的长度）相差甚远。然而，这些实验是在静态条件下进行的。虽然我们的研究结果代表了对ASM生物学理解的重大进步，但我们的离体设置可以改进以更接近地模拟体内条件。** ASM在体内运行时调用的长度不是静态的。肺是一个动态的器官，需要大量和连续的容积变化来完成其通气功能。这些体积的变化导致了ASM长度的振荡变化。因此，除了将ASM设置为原位长度外，还需要在模拟体内肺体积变化的长度变化过程中研究ASM。该计划的目标是在离体环境中确定ASM在人类支气管力学中的作用，该环境重现了ASM在体内运作的动态环境。**本研究项目旨在：*1在ASM在体内可经历的长度范围内的动态和重复的延长和缩短周期中，确定不同ASM激活水平下人类支气管ASM的长度-力关系。*2-确定长度变化的速率，在体内可能发生的速率范围内，是否影响ASM长度-力关系。*3-确定用于激活ASM的痉挛素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，估计不同大小单个气道中ASM激活和长度变化对ASM缩短、气道狭窄和气流阻力的影响。**本项目将测定不同激活水平下人体支气管在生理范围和长度变化速率下ASM产生的力的大小。它还将预测长度和ASM激活如何影响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以影响肺功能。我们认为，在一个模拟体内肺体积永久变化的动态系统中，更好地表征ASM的长度-力关系是理解ASM生理功能的先决条件。该项目将为呼吸生理学、生物力学、组织生物学、药理学和计算建模分析方面的高素质人才提供尖端专业知识。

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.