Division of Asthma, Allergy and Lung Biology, King's College London School of Medicine, King's Health Partners, London, UK.
State Key Laboratory of Respiratory Disease, Guangzhou Medical College, Guangzhou, China.
Lancet. 2015 Feb 26;385 Suppl 1:S51. doi: 10.1016/S0140-6736(15)60366-X.
Exercise capacity in chronic obstructive pulmonary disease (COPD) is limited by both breathlessness and leg muscle fatigue. Neural respiratory drive, measured as diaphragm electromyogram (EMGdi) activity expressed as a proportion of maximum (EMGdi%max), quantifies the mechanical load on the respiratory muscles and relates closely to breathlessness. We tested the hypothesis that end-exercise EMGdi%max would be higher in patients stopping because of breathlessness than in those limited by leg fatigue.
EMGdi, ventilation, rate of oxygen consumption (VO2), and ventilatory reserve (ventilation/maximum ventilatory volume ratio [VE/MVV]) were measured continuously in patients with COPD during exhaustive cycle ergometry. EMGdi was measured with a multipair oesophageal catheter passed per-nasally. Differences in physiological variables between groups of patients stopping because of breathlessness, leg fatigue, or both were assessed with one-way ANOVA.
23 patients were included (median FEV1, 39% of predicted, IQR 30·0-56·8). End-exercise EMGdi%max was significantly higher in patients stopping exercise because of breathlessness (n=12, median EMGdi%max 75·7% [IQR 69·5-77·1]) than in those stopping because of leg fatigue (n=8, 44·1 [39·4-63·3]) or both (n=3, 74·1 [63·6-81·2]) (p=0·02). There were no significant differences between the groups in end-exercise ventilation (breathlessness 25·7 L/min [16·3-32·0] vs leg fatigue 31·5 [20·9-39·6] vs both 22·0 [17·7-35·7]), VO2, (13·4 mL/min per kg [11·6-14·2] vs 12·1 [10·4-14·8] vs 9·4 [9·1-12·4]), or VE/MVV (80·4% [72·6-88·3] vs 57·8 [52·1-92·6] vs 63·9 [34·5-88·9]).
These results suggest that patients limited by breathlessness due to ventilatory constraints can be identified as those reaching near-maximum levels of neural respiratory drive during exercise. Measurement of EMGdi%max during exercise could prove useful in identifying patients whose functional performance would be best optimised by improvment in pulmonary mechanics rather than interventions to train peripheral muscle groups.
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慢性阻塞性肺疾病（COPD）患者的运动能力受到呼吸困难和腿部肌肉疲劳的限制。膈肌肌电图（EMGdi）活性作为最大（EMGdi%max）的比例表示，可测量神经呼吸驱动，定量呼吸肌的机械负荷，并与呼吸困难密切相关。我们假设，由于呼吸困难而停止运动的患者的终末运动 EMGdi%max 会高于因腿部疲劳而停止运动的患者。
在 COPD 患者进行耗竭性踏车运动期间，连续测量膈肌 EMGdi、通气、摄氧量（VO2）和通气储备（通气/最大通气量比值[VE/MVV]）。通过经鼻传递的多对食管导管测量 EMGdi。使用单向方差分析评估因呼吸困难、腿部疲劳或两者均停止运动的患者组之间生理变量的差异。
共纳入 23 名患者（中位 FEV1，预测值的 39%，IQR 30.0-56.8）。由于呼吸困难而停止运动的患者（n=12，终末运动 EMGdi%max 为 75.7%[IQR 69.5-77.1%]）的终末运动 EMGdi%max 显著高于因腿部疲劳（n=8，44.1%[39.4-63.3]）或两者均停止运动的患者（n=3，74.1%[63.6-81.2]）（p=0.02）。呼吸困难组、腿部疲劳组和两者均停止运动组的终末运动通气（呼吸困难 25.7 L/min[16.3-32.0]、腿部疲劳 31.5[20.9-39.6]、两者均 22.0[17.7-35.7]）、VO2（13.4 mL/min/kg[11.6-14.2]、12.1[10.4-14.8]、9.4[9.1-12.4]）和 VE/MVV（80.4%[72.6-88.3]、57.8[52.1-92.6]、63.9[34.5-88.9]）均无显著差异。
这些结果表明，由于通气限制而呼吸困难受限的患者可以被识别为在运动过程中达到接近最大神经呼吸驱动水平的患者。在运动过程中测量 EMGdi%max 可能有助于确定哪些患者的功能表现通过改善肺力学而不是干预训练外周肌群来优化。
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