Barbini Paolo, Brighenti Chiara, Cevenini Gabriele, Gnudi Gianni
Dipartimento di Chirurgia e Bioingegneria, Università di Siena, Viale Bracci 2, Siena, Italy.
Ann Biomed Eng. 2005 Apr;33(4):518-30. doi: 10.1007/s10439-005-2511-6.
A nonlinear dynamic morphometric model of breathing mechanics during artificial ventilation is described. On the basis of the Weibel symmetrical representation of the tracheo-bronchial tree, the model accurately accounts for the geometrical and mechanical characteristics of the conductive zone and packs the respiratory zone into a viscoelastic Voigt body. The model also accounts for the main mechanisms limiting expiratory flow (wave speed limitation and viscous flow limitation), in order to reproduce satisfactorily, under dynamic conditions, the expiratory flow limitation phenomenon occurring in normal subjects when the difference between alveolar pressure and tracheal pressure (driving pressure) is high. Several expirations characterized by different levels of driving pressure are simulated and expiratory flow limitation is detected by plotting the isovolume pressure-flow curves. The model is used to study the time course of resistance and total cross-sectional area as well as the ratio of fluid velocity to wave speed (speed index), in conductive airway generations. The results highlight that the coupling between dissipative pressure losses and airway compliance leads to onset of expiratory flow limitation in normal lungs when driving pressure is increased significantly by applying a subatmospheric pressure to the outlet of the ventilator expiratory channel; wave speed limitation becomes predominant at still higher driving pressures.
本文描述了一种人工通气期间呼吸力学的非线性动态形态计量模型。基于气管支气管树的韦贝尔对称表示，该模型准确地考虑了传导区的几何和力学特性，并将呼吸区打包成一个粘弹性沃伊特体。该模型还考虑了限制呼气流量的主要机制（波速限制和粘性流限制），以便在动态条件下令人满意地再现正常受试者在肺泡压力与气管压力之差（驱动压力）较高时出现的呼气流量限制现象。模拟了几种以不同驱动压力水平为特征的呼气，并通过绘制等容压力-流量曲线来检测呼气流量限制。该模型用于研究传导气道各级的阻力和总横截面积的时间进程以及流体速度与波速之比（速度指数）。结果表明，当通过对呼吸机呼气通道出口施加低于大气压的压力使驱动压力显著增加时，耗散压力损失与气道顺应性之间的耦合导致正常肺中呼气流量限制的开始；在更高的驱动压力下，波速限制变得占主导地位。
