Polak Adam G, Lutchen Kenneth R
Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA.
Ann Biomed Eng. 2003 Sep;31(8):891-907. doi: 10.1114/1.1588651.
We present a computational model to predict maximal expiration through a morphometry-based asymmetrical bronchial tree. A computational model with the Horsfield-like geometry of the airway structure, including wave-speed flow limitation and taking into consideration separate airflows from several independent alveolar compartments has been derived. The airflow values are calculated for quasistatic conditions by solving a system of nonlinear differential equations describing static pressure losses along the airway branches. Calculations done for succeeding lung volumes result in the semidynamic maximal expiratory flow-volume (MEFV) curve. Simulations performed show that the model captures the main phenomena observed in vivo during forced expiration: effort independence of the flow-volume curve for the most of vital capacity, independence of limited flow on the properties of airways downstream to the choke points, characteristic differences of lung regional pressures and volumes, and a shape of their variability during exhalation. Some new insights into the flow limitation mechanism were achieved. First, flow limitation begins at slightly different time instants in individual branches of the bronchial tree, however after a short period of time, all regional flows are limited in a parallel fashion. Hence, total flow at the mouth is limited for most of the expired lung volume. Second, each of the airway branches contribute their own flow-volume shape and just these individual flows constitute the measured MEFV curve. Third, central airway heterogeneity can play a crucial role in modification of the entire flow. Fourth, the bronchial tree asymmetry is responsible for a nongravitational component of regional volume variability. Finally, increased inhomogeneity yields results that cannot be explained nor re-created with the use of a symmetrical structure of the bronchial tree.
我们提出了一种计算模型，用于通过基于形态测量的不对称支气管树预测最大呼气量。已经推导了一种具有类似霍斯菲尔德气道结构几何形状的计算模型，该模型包括波速流量限制，并考虑了来自几个独立肺泡腔的单独气流。通过求解描述气道分支静压损失的非线性微分方程组，计算准静态条件下的气流值。对后续肺容积进行的计算得出半动态最大呼气流量-容积（MEFV）曲线。进行的模拟表明，该模型捕捉了用力呼气过程中体内观察到的主要现象：肺活量大部分时间流量-容积曲线的用力独立性、阻塞点下游气道特性对受限流量的独立性、肺区域压力和容积的特征差异以及呼气过程中它们变化的形状。对流量限制机制有了一些新的认识。首先，支气管树各分支的流量限制开始时间略有不同，但经过短时间后，所有区域流量以平行方式受限。因此，在大部分呼出肺容积期间，口腔处的总流量受限。其次，每个气道分支都有其自身的流量-容积形状，正是这些个体流量构成了测量的MEFV曲线。第三，中央气道异质性在改变整个流量方面可能起关键作用。第四，支气管树不对称是区域容积变异性非重力分量的原因。最后，增加的不均匀性产生的结果无法用支气管树的对称结构来解释或重现。
