Beck J, Sinderby C, Lindström L, Grassino A
Department of Physiology, McGill University, Montreal, Quebec H3G 1Y6.
J Appl Physiol (1985). 1998 Sep;85(3):1123-34. doi: 10.1152/jappl.1998.85.3.1123.
The use of esophageal recordings of the diaphragm electromyogram (EMG) signal strength to evaluate diaphragm activation during voluntary contractions in humans has recently been criticized because of a possible artifact created by changes in lung volume. Therefore, the first aim of this study was to evaluate whether there is an artifactual influence of lung volume on the strength of the diaphragm EMG during voluntary contractions. The second aim was to measure the required changes in activation for changes in lung volume at a given tension, i.e., the volume-activation relationship of the diaphragm. Healthy subjects (n = 6) performed contractions of the diaphragm at different transdiaphragmatic pressure (Pdi) targets (range 20-160 cmH2O) while maintaining chest wall configuration constant at different lung volumes. The diaphragm EMG was recorded with a multiple-array esophageal electrode, with control of signal contamination and electrode positioning. The effects of lung volume on the EMG were studied by comparing the crural diaphragm EMG root mean square (RMS), an index of crural diaphragm activation, with an index of global diaphragm activation obtained by normalizing Pdi to the maximum Pdi at the given muscle length (Pdi/Pdimax@L) at the different lung volumes. We observed a direct relationship between RMS and Pdi/Pdimax@L independent of diaphragm length. The volume-activation relationship of the diaphragm was equally affected by changes in lung volume as the volume-Pdi relationship (60% change from functional residual capacity to total lung capacity). We conclude that the RMS of the diaphragm EMG is not artifactually influenced by lung volume and can be used as a reliable index of diaphragm activation. The volume-activation relationship can be used to infer changes in the length-tension relationship of the diaphragm at submaximal activation/contraction levels.
由于肺容量变化可能产生伪影，近期利用食管记录膈肌肌电图（EMG）信号强度来评估人体自主收缩时膈肌激活情况的方法受到了批评。因此，本研究的首要目的是评估肺容量在自主收缩期间对膈肌EMG强度是否存在伪影影响。第二个目的是测量在给定张力下肺容量变化所需的激活变化，即膈肌的容量 - 激活关系。健康受试者（n = 6）在不同的跨膈压（Pdi）目标（范围为20 - 160 cmH₂O）下进行膈肌收缩，同时在不同肺容量下保持胸壁构型恒定。使用多阵列食管电极记录膈肌EMG，并控制信号污染和电极定位。通过比较膈脚膈肌EMG均方根（RMS）（膈脚膈肌激活指标）与在不同肺容量下将Pdi归一化为给定肌肉长度下的最大Pdi（Pdi / Pdimax@L）所获得的整体膈肌激活指标，研究肺容量对EMG的影响。我们观察到RMS与Pdi / Pdimax@L之间存在直接关系，且与膈肌长度无关。膈肌的容量 - 激活关系受肺容量变化的影响与容量 - Pdi关系相同（从功能残气量到肺总量变化60%）。我们得出结论，膈肌EMG的RMS不受肺容量的伪影影响，可作为膈肌激活的可靠指标。容量 - 激活关系可用于推断在次最大激活/收缩水平下膈肌长度 - 张力关系的变化。
