Cheng W, DeLong D S, Franz G N, Petsonk E L, Frazer D G
Department of Physiology, West Virginia University School of Medicine, Maorgantown 26506, USA.
Respir Physiol. 1995 Dec;102(2-3):205-15. doi: 10.1016/0034-5687(95)00055-0.
The recruitment and derecruitment of lung units is one explanation of the hysteresis observed in an excised lung during inflation and deflation. A simplified model has been proposed in which the recruitment-derecruitment process is a function of end-expiratory pressure (Frazer, D.G., K.C. Weber and G.N. Franz, Respir. Physiol. 61: 277-288, 1985). The object of this study was to test this model with three experimental procedures. During the first set of experiments, progressively larger pressure-volume (PL-VL) loops were recorded with end-expiratory pressure held at either -5 cmH2O, where all lung units are assumed to be closed, or +5 cmH2O, where all recruited lung units are assumed to be open. In the first case hysteresis is maximal, in the second, minimal. The difference in hysteresis is presumed to arise from the recruitment-derecruitment process. In the second set of experiments, excised lungs are slowly inflated and then deflated at a constant rate while constant-amplitude sinusoidal volume oscillations are superimposed. The end-expiratory pressure of the superimposed loops gradually rose as the lung was inflated and fell as the lung was deflated. Hysteresis was minimal when end-expiratory pressure was above 4 +/- 1 cmH2O even as peak-to-peak loop pressure greatly varied. This supports the notion of an end-expiratory pressure dependent mechanism of recruitment/derecruitment. During the third set of experiments lungs were inflated to either 50%, 75%, or 100% TLC. Volumes of air were then withdrawn and replaced so that the initial volume was restored in sinusoidal fashion as the amplitude of the volume excursions increased. For PL-VL loops with end-expiratory pressures between +4 and -2 cmH2O, pressure amplitudes rose and the hysteresis index (loop area/tidal volume) increased, regardless of the initial lung volume. These results are consistent with the previously described model of Frazer et al. (1985) which assumed that PL-VL curves can be divided into an 'opening' region, an 'open' region and a 'closing' region and that the demarcation of these regions depends on transpulmonary pressure, specifically end-expiratory pressure, and to a much lesser degree on lung volume.
肺单位的募集和去募集是在离体肺膨胀和放气过程中观察到滞后现象的一种解释。有人提出了一个简化模型，其中募集 - 去募集过程是呼气末压力的函数（Frazer, D.G., K.C. Weber和G.N. Franz, 《呼吸生理学》61: 277 - 288, 1985）。本研究的目的是用三种实验方法来检验这个模型。在第一组实验中，当呼气末压力保持在 -5 cmH₂O（假设所有肺单位均关闭）或 +5 cmH₂O（假设所有募集的肺单位均开放）时，记录逐渐增大的压力 - 容积（Pₗ - Vₗ）环。在第一种情况下滞后现象最大，在第二种情况下最小。滞后现象的差异被认为是由募集 - 去募集过程引起的。在第二组实验中，离体肺缓慢膨胀，然后以恒定速率放气，同时叠加恒定幅度的正弦容积振荡。叠加环的呼气末压力随着肺的膨胀而逐渐升高，随着肺的放气而降低。即使峰 - 峰环压力变化很大，当呼气末压力高于4 ± 1 cmH₂O时滞后现象最小。这支持了募集/去募集的呼气末压力依赖性机制的观点。在第三组实验中，肺被膨胀至肺总量（TLC）的50%、75%或100%。然后抽出并替换空气量，使得随着容积波动幅度增加，初始容积以正弦方式恢复。对于呼气末压力在 +4和 -2 cmH₂O之间的Pₗ - Vₗ环，无论初始肺容积如何，压力幅度都会升高，滞后指数（环面积/潮气量）也会增加。这些结果与Frazer等人（1985）先前描述的模型一致，该模型假设Pₗ - Vₗ曲线可分为一个“开放”区域、一个“已开放”区域和一个“关闭”区域，并且这些区域的划分取决于跨肺压，特别是呼气末压力，而在很大程度上取决于肺容积。
