Baarends E M, Schols A M, Akkermans M A, Wouters E F
Department of Pulmonology, Maastricht University, Maastricht, The Netherlands.
Thorax. 1997 Nov;52(11):981-6. doi: 10.1136/thx.52.11.981.
It has recently been reported that total daily energy expenditure (TDE) is increased in patients with chronic obstructive pulmonary disease (COPD) and it was hypothesised that these patients may have a decreased mechanical efficiency during activities. The purpose of the present study was to measure the mechanical efficiency of submaximal leg exercise, and to characterise patients with a potentially low efficiency in terms of body composition, resting energy expenditure, lung function, and symptom limited exercise performance.
Metabolic and ventilatory variables were measured breath by breath during submaximal cycle ergometry exercise performed at 50% of symptom limited achieved maximal load in 33 clinically stable patients with COPD (23 men) with forced expiratory volume in one second (FEV1) of 40 (12)% predicted. Net mechanical efficiency was calculated adjusting for resting energy expenditure (REE).
Median mechanical efficiency was 15.5% and ranged from 8.5% to 22.7%. Patients with an extremely low mechanical efficiency (< 17%, n = 21) demonstrated an increased VO2/VE compared with those with a normal efficiency (median difference 4.7 ml/l, p = 0.005) during submaximal exercise. There was no difference between the groups differentiated by mechanical efficiency in blood gas tensions at rest, airflow obstruction, respiratory muscle strength, hyperinflation at rest, resting energy expenditure or body composition. There was a significant difference in total airways resistance (92% predicted, p = 0.03) between the groups differentiated by mechanical efficiency.
It is concluded that many patients with severe COPD have decreased mechanical efficiency. Furthermore, based on the results of this study it is hypothesised that an increased oxygen cost of breathing during exercise contributes to the decreased mechanical efficiency.
最近有报道称，慢性阻塞性肺疾病（COPD）患者的每日总能量消耗（TDE）增加，据推测这些患者在活动期间的机械效率可能降低。本研究的目的是测量次最大强度腿部运动的机械效率，并根据身体成分、静息能量消耗、肺功能和症状限制运动表现来描述潜在低效率患者的特征。
对33例临床稳定的COPD患者（23例男性）进行次最大强度的蹬车运动，运动强度为症状限制下达到的最大负荷的50%，期间逐次测量代谢和通气变量，这些患者的一秒用力呼气容积（FEV1）为预测值的40（12）%。计算净机械效率，并对静息能量消耗（REE）进行校正。
机械效率中位数为15.5%，范围为8.5%至22.7%。与机械效率正常的患者相比，机械效率极低（<17%，n = 21）的患者在次最大强度运动期间的VO2/VE增加（中位数差异为4.7 ml/l，p = 0.005）。在静息血气张力、气流阻塞、呼吸肌力量、静息时肺过度充气、静息能量消耗或身体成分方面，按机械效率区分的各组之间没有差异。按机械效率区分的各组之间的总气道阻力存在显著差异（预测值的92%，p = 0.03）。
得出的结论是，许多重度COPD患者的机械效率降低。此外，根据本研究结果推测，运动期间呼吸的氧消耗增加导致了机械效率降低。
