Hamnegård C H, Wragg S, Mills G, Kyroussis D, Road J, Daskos G, Bake B, Moxham J, Green M
Respiratory Muscle Laboratory, National Heart and Lung Institute, Brompton Hospital, London, UK.
Eur Respir J. 1995 Sep;8(9):1532-6.
Diaphragm strength can be assessed by measurement of transdiaphragmatic pressure (Pdi) in response to stimulation of the phrenic nerves. The length-tension relationship of the diaphragm can be studied by measuring twitch Pdi over the range of lung volume. Previous studies of the relationship between lung volume and diaphragm strength have used the technique of electrical stimulation of the phrenic nerves. In these studies, the phenomenon of twitch potentiation has not been taken into account. It has previously been shown that prior contraction of the diaphragm can greatly enhance the twitch response, thus affecting the measurements. The aim of this study was to investigate the relationship between unpotentiated twitch Pdi and lung volume for volumes ranging from residual volume (RV) to total lung capacity (TLC) in normal subjects. Great care was taken to avoid muscle potentiation. For this purpose, we stimulated the phrenic nerves with a magnetic stimulator. In addition, we used positive pressure to inflate the lungs to high lung volumes. The impact of twitch potentiation on the length-tension relationship was investigated by subjects making maximum inspiratory efforts prior to phrenic nerve stimulation. The unpotentiated twitch Pdi decreased in a linear fashion with increasing lung volume over the full range of vital capacity by 0.54 kPa.L-1. Potentiation increased twitch Pdi by 40% at FRC and the effect was similar, in absolute terms, at all lung volumes. In relative terms, the effect of potentiation became greater as lung volume increased, and more than doubled twitch Pdi at TLC. With increasing lung volume, there is a linear fall in unpotentiated twitch Pdi with a slope that is less steep, over the same range of absolute lung volume, than previously reported. When assessing diaphragm strength by the twitch technique, it is essential to control for lung volume and equally important to control for twitch potentiation.
可通过测量膈神经受刺激时的跨膈压（Pdi）来评估膈肌力量。通过在肺容积范围内测量单刺激Pdi，可研究膈肌的长度-张力关系。先前关于肺容积与膈肌力量关系的研究采用了膈神经电刺激技术。在这些研究中，单刺激增强现象未被考虑在内。此前已表明，膈肌的预先收缩可极大增强单刺激反应，从而影响测量结果。本研究的目的是在正常受试者中，研究从残气量（RV）到肺总量（TLC）范围内，未经增强的单刺激Pdi与肺容积之间的关系。我们格外小心以避免肌肉增强。为此，我们使用磁刺激器刺激膈神经。此外，我们使用正压将肺充气至高肺容积。通过让受试者在膈神经刺激前进行最大吸气努力，研究单刺激增强对长度-张力关系的影响。在肺活量的整个范围内，未经增强的单刺激Pdi随肺容积增加呈线性下降，斜率为0.54 kPa·L-1。在功能残气量（FRC）时，增强使单刺激Pdi增加40%，并且在所有肺容积下，绝对而言，效果相似。相对而言，随着肺容积增加，增强的效果变得更大，在肺总量时单刺激Pdi增加超过一倍。随着肺容积增加，未经增强的单刺激Pdi呈线性下降，在相同的绝对肺容积范围内，其斜率比先前报道的更平缓。当通过单刺激技术评估膈肌力量时，控制肺容积至关重要，同样重要的是控制单刺激增强。
