Department of Respiratory Medicine, Institute for Lung Health, University Hospitals of Leicester NHS Trust, Glenfield Hospital, Leicester, UK.
Respir Med. 2010 May;104(5):675-81. doi: 10.1016/j.rmed.2009.11.012. Epub 2009 Dec 8.
It is well documented that plasma ammonia accumulates during exercise under conditions of metabolic stress. Metabolic stress (when skeletal muscle ATP supply fails to meet demand) occurs at low work rates during cycling in patients with COPD, but not been described during walking. Walking is an important activity for many patients with COPD and is commonly prescribed in pragmatic outpatient pulmonary rehabilitation programmes. In this study we explored whether metabolic stress occurs during incremental walking at the low work rates these patients achieve.
Twenty-nine subjects with stable COPD [mean(SD) age 68(7)years, FEV(1) 50(19)% predicted] performed maximal cardiopulmonary exercise tests on a cycle ergometer and treadmill. Plasma ammonia concentration was measured at rest, 1 and 2min of exercise, peak exercise and 2min recovery.
Subjects achieved mean(SD) cycle work rate of 57(20)W with VO(2max) 15.5(4.6)ml/min per kg, and treadmill distance 284(175)m with VO(2peak) 16.8(4.2)ml/min per kg. Plasma ammonia concentration rose significantly (p<0.001) with walking [mean(SEM) change 24.7(3.8)micromol/l] and cycling [mean(SEM) change 35.2(4.3)micromol/l], but peak exercise ammonia was lower in walking (p<0.01). In a subgroup of subjects (n=7) plasma ammonia did not rise during either cycling or walking despite similar lactate rise and peak exercise indices.
Our data indicate that failure of muscle ATP re-synthesis to meet demand and development of metabolic stress can occur during walking in COPD patients at the low work rates these patients achieve. This may therefore be a factor contributing to exercise limitation independent of ventilatory limitation.
有大量文献记载，在代谢应激条件下运动时，血浆氨会积累。在 COPD 患者进行低功 cycling 时会发生代谢应激（当骨骼肌 ATP 供应无法满足需求时），但在行走时尚未描述。行走是许多 COPD 患者的重要活动，并且在实用的门诊肺康复计划中经常规定。在这项研究中，我们探讨了在这些患者达到的低功 walking 时是否会发生代谢应激。
29 名稳定的 COPD 患者[平均（SD）年龄 68（7）岁，FEV（1）50（19）%预计值]在循环测功仪和跑步机上进行了最大心肺运动测试。在休息时、运动 1 和 2 分钟时、峰值运动时和 2 分钟恢复时测量血浆氨浓度。
患者在 cycle 上实现的平均（SD）功为 57（20）W，VO（2max）为 15.5（4.6）ml/min/kg，在 treadmill 上的距离为 284（175）m，VO（2peak）为 16.8（4.2）ml/min/kg。血浆氨浓度显着升高（p<0.001）[mean（SEM）变化 24.7（3.8）micromol/l]，与 walking [mean（SEM）变化 35.2（4.3）micromol/l]相比，但 walking 时的峰值运动氨浓度较低（p<0.01）。在一组患者（n=7）中，尽管乳酸升高和峰值运动指数相似，但在 cycling 或 walking 期间，血浆氨并未升高。
我们的数据表明，在 COPD 患者达到的低功 walking 时，肌肉 ATP 再合成无法满足需求，代谢应激可能会发生。因此，这可能是独立于通气限制导致运动受限的一个因素。
