De Troyer André
Chest Service, Erasme Univ. Hospital, 1070 Brussels, Belgium.
J Appl Physiol (1985). 2008 Sep;105(3):887-93. doi: 10.1152/japplphysiol.00198.2008. Epub 2008 Jul 17.
To assess the coupling between a particular hemidiaphragm and the individual lungs, the left and right phrenic nerves were separately stimulated in anesthetized dogs, and the mean changes in pleural pressure over the two lungs were evaluated by measuring the changes in airway opening pressure (DeltaPao) in the two bronchial trees. Stimulation induced a fall in Pao in both lungs. However, DeltaPao in the contralateral lung was only 65% of that in the ipsilateral lung. Thus, although the canine ventral mediastinum is a delicate structure, it sustained a significant pressure gradient. The hypothesis was then considered that this gradient was allowed to develop through the stretching and stiffening of the mediastinum caused by the descent of the diaphragm, and it was tested by measuring DeltaPao in the two lungs during isolated, unilateral contraction of the inspiratory intercostal muscles. In this condition, DeltaPao in the contralateral lung was 92% of that in the ipsilateral lung. A model analysis of the respiratory system led to the estimate that mediastinal elastance was approximately 25 times greater during hemidiaphragmatic contraction than during unilateral intercostal contraction. These observations indicate that 1) a particular hemidiaphragm has an expanding action on both lungs and 2) during contraction, however, it makes the mediastinum stiffer so that the pressure transmission from the ipsilateral to the contralateral pleural cavity is reduced. These observations imply that the mediastinum may play a significant role in determining the pressure-generating ability of the diaphragm.
为了评估特定半侧膈肌与各肺之间的耦合情况，在麻醉犬身上分别刺激左右膈神经，并通过测量两个支气管树中气道开口压力（ΔPao）的变化来评估两肺胸膜压力的平均变化。刺激导致两肺的Pao下降。然而，对侧肺的ΔPao仅为同侧肺的65%。因此，尽管犬的腹侧纵隔是一个精细的结构，但它承受着显著的压力梯度。于是有人提出假说，认为这种梯度是由于膈肌下降导致纵隔伸展和变硬而形成的，并通过在吸气肋间肌单侧孤立收缩期间测量两肺的ΔPao进行了验证。在这种情况下，对侧肺的ΔPao为同侧肺的92%。对呼吸系统的模型分析得出的估计是，半侧膈肌收缩期间的纵隔弹性大约是单侧肋间肌收缩期间的25倍。这些观察结果表明：1）特定半侧膈肌对两肺均有扩张作用；2）然而，在收缩过程中，它会使纵隔变硬，从而减少从同侧胸膜腔到对侧胸膜腔的压力传递。这些观察结果意味着纵隔可能在决定膈肌的压力产生能力方面发挥重要作用。
