Wilson T A, Boriek A M, Rodarte J R
Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
J Appl Physiol (1985). 1998 Dec;85(6):2284-90. doi: 10.1152/jappl.1998.85.6.2284.
The mechanical advantage (mu) of a respiratory muscle is defined as the respiratory pressure generated per unit muscle mass and per unit active stress. The value of mu can be obtained by measuring the change in the length of the muscle during inflation of the passive lung and chest wall. We report values of mu for the muscles of the canine diaphragm that were obtained by measuring the lengths of the muscles during a passive quasistatic vital capacity maneuver. Radiopaque markers were attached along six muscle bundles of the costal and two muscle bundles of the crural left hemidiaphragms of four bred-for-research beagle dogs. The three-dimensional locations of the markers were obtained from biplane video-fluoroscopic images taken at four volumes during a passive relaxation maneuver from total lung capacity to functional residual capacity in the prone and supine postures. Muscle lengths were determined as a function of lung volume, and from these data, values of mu were obtained. Values of mu are fairly uniform around the ventral midcostal and crural diaphragm but significantly lower at the dorsal end of the costal diaphragm. The average values of mu are -0.35 +/- 0.18 and -0.27 +/- 0.16 cmH2O. g-1. kg-1. cm-2 in the prone and supine dog, respectively. These values are 1. 5-2 times larger than the largest values of mu of the intercostal muscles in the supine dog. From these data we estimate that during spontaneous breathing the diaphragm contributes approximately 40% of inspiratory pressure in the prone posture and approximately 30% in the supine posture. Passive shortening, and hence mu, in the upper one-third of inspiratory capacity is less than one-half of that at lower lung volume. The lower mu is attributed primarily to a lower abdominal compliance at high lung volume.
呼吸肌的机械优势（μ）定义为单位肌肉质量和单位主动应力产生的呼吸压力。μ的值可通过测量被动肺和胸壁充气时肌肉长度的变化来获得。我们报告了通过在被动准静态肺活量动作期间测量犬膈肌肌肉长度而获得的μ值。在四只用于研究的比格犬的肋部六个肌束和左侧半膈脚的两个肌束上附着了不透射线的标记物。标记物的三维位置是从在俯卧位和仰卧位从肺总量到功能残气量的被动放松动作期间四个容积下拍摄的双平面视频荧光图像中获得的。肌肉长度被确定为肺容积的函数，并根据这些数据获得μ值。μ值在腹侧中肋部和膈脚周围相当均匀，但在肋部膈肌背侧末端显著较低。在俯卧位和仰卧位犬中，μ的平均值分别为-0.35±0.18和-0.27±0.16 cmH₂O·g⁻¹·kg⁻¹·cm⁻²。这些值比仰卧位犬肋间肌的最大μ值大1.5 - 2倍。根据这些数据，我们估计在自主呼吸期间，膈肌在俯卧位时贡献约40%的吸气压力，在仰卧位时贡献约30%的吸气压力。在吸气容量上三分之一时的被动缩短以及因此的μ小于低肺容积时的一半。较低的μ主要归因于高肺容积时较低的腹部顺应性。
