Sprung J, Deschamps C, Margulies S S, Hubmayr R D, Rodarte J R
Department of Medicine Baylor College of Medicine, Houston, Texas.
J Appl Physiol (1985). 1990 Dec;69(6):2296-302. doi: 10.1152/jappl.1990.69.6.2296.
The in situ lengths of muscle bundles of the crural and three regions of the costal diaphragm between origin and insertion were determined with a video roentgenographic technique in dogs. At total lung capacity (TLC) in both the prone and supine positions, the length of the diaphragm is not significantly different from the unstressed excised length, suggesting that the diaphragm is not under tension at TLC and that there is a hydrostatic gradient of pleural pressure on the diaphragmatic surface. Except for the ventral region of the costal diaphragm, which does not change length at lung volumes greater than 70% TLC, all other regions are stretched during passive deflations from TLC. Therefore below TLC the diaphragm is under passive tension and supports a transdiaphragmatic pressure (Pdi). The length of the diaphragm relative to its unstressed length is not uniform at functional residual capacity (FRC) and does not follow a strict vertical gradient that reverses when the animal is changed from the supine to the prone position. By inference, the length of muscle bundles is determined by factors other than the vertical gradient of Pdi. During mechanical ventilation, regional shortening is identical to the passive deflation length-volume relationship near FRC. Prone and supine FRC is the same, but the diaphragm is slightly shorter in the prone position. In both positions, during spontaneous ventilation there are no consistent differences in regional fractional shortening, despite regional differences in initial length relative to unstressed length.
采用视频X线照相技术测定了犬下肢和肋膈三个区域的肌束在起点与止点之间的原位长度。在全肺容量（TLC）时，无论犬处于俯卧位还是仰卧位，膈肌长度与未受力的离体长度相比均无显著差异，这表明在TLC时膈肌不受张力，且膈肌表面存在胸膜腔内压的流体静力梯度。除肋膈腹侧区域在肺容量大于TLC的70%时长度不变外，所有其他区域在从TLC被动放气过程中均被拉长。因此，在TLC以下，膈肌承受被动张力并支撑跨膈压（Pdi）。在功能残气量（FRC）时，膈肌相对于其未受力长度的长度并不均匀，且不遵循严格的垂直梯度，当动物从仰卧位变为俯卧位时该梯度也不会反转。由此推断，肌束长度由Pdi垂直梯度以外的因素决定。在机械通气期间，区域缩短与FRC附近的被动放气长度-容积关系相同。俯卧位和仰卧位的FRC相同，但俯卧位时膈肌略短。在两个体位下，自主通气期间区域缩短分数均无一致差异，尽管相对于未受力长度，初始长度存在区域差异。
