Debigaré R, Côte C H, Hould F S, LeBlanc P, Maltais F
Centre de recherche, Hôpital Laval, Institut universitaire de Cardiologie et de Pneumologie de l'Université Laval, Sainte-Foy, QC, Canada.
Eur Respir J. 2003 Feb;21(2):273-8. doi: 10.1183/09031936.03.00036503.
Peripheral muscle weakness is common in chronic obstructive pulmonary disease (COPD) but it is still under debate whether weakness is due to atrophy or contractile dysfunction. In vitro and in vivo contractile properties of the vastus lateralis muscle were studied in 16 patients with stable COPD (forced expiratory volume in one second 39 +/- 16% of predicted, age 67 +/- 4 yrs (mean +/- sD)) and nine sedentary control subjects. Isometric knee extensor strength was measured while mid-thigh muscle cross-sectional area (MTMCSA) was obtained using computed tomography. Muscle strips from the vastus lateralis obtained through open biopsy were rapidly suspended in an oxygenated Krebs-Ringer solution that was maintained at 35 degrees C with a pH of 7.40 to study their contractile properties. The isometric knee extensors strength/MTMCSA ratio was 0.50 +/- 0.08 versus 0.58 +/- 0.06 kg x cm(-2) for COPD and control subjects, respectively. The muscle bundle cross-sectional area (CSA) was 4.6 +/- 2.1 and 4.4 +/- 3.1 mm(-2), the length at which active tension was maximum was 15 +/- 4 and 15 +/- 3 mm, and maximal isometric peak forces normalised for CSA were 4.3 +/- 2.7 and 4.8 +/- 2.6 N x cm(-2) for COPD and control subjects, respectively. The force/frequency relationship tended to be shifted to the right in patients with COPD, meaning that a higher stimulation frequency was necessary to produce the same relative force. Patients with COPD had a lower proportion of type I fibre than controls (26 +/- 12% versus 39 +/- 11%) with reciprocal significant increase in type IIb fibre proportion (20+/-16% versus 8 +/- 4%). The proportion of type IIa fibres was similar between the two groups. These results suggest that the contractile properties of the vastus lateralis are preserved in patients with chronic obstructive pulmonary disease. Therefore, the reduction in the quadriceps strength in patients with chronic obstructive pulmonary disease cannot be explained on the basis of an alteration of the contractile apparatus.
外周肌肉无力在慢性阻塞性肺疾病（COPD）中很常见，但肌肉无力是由于萎缩还是收缩功能障碍仍存在争议。对16例稳定期COPD患者（一秒用力呼气容积为预测值的39±16%，年龄67±4岁（均值±标准差））和9名久坐的对照者的股外侧肌进行了体外和体内收缩特性研究。测量等长伸膝力量，同时使用计算机断层扫描获取大腿中部肌肉横截面积（MTMCSA）。通过开放活检获取的股外侧肌肌肉条迅速悬浮于pH值为7.40、温度保持在35℃的充氧Krebs-Ringer溶液中，以研究其收缩特性。COPD患者和对照者的等长伸膝力量/MTMCSA比值分别为0.50±0.08和0.58±0.06kg·cm⁻²。肌肉束横截面积（CSA）分别为4.6±2.1和4.4±3.1mm⁻²，产生最大主动张力时的长度分别为15±4和15±3mm，COPD患者和对照者经CSA标准化后的最大等长峰值力分别为4.3±2.7和4.8±2.6N·cm⁻²。COPD患者的力/频率关系倾向于右移，这意味着需要更高的刺激频率才能产生相同的相对力。COPD患者的I型纤维比例低于对照者（26±12%对39±11%），IIb型纤维比例相应显著增加（20±16%对8±4%）。两组间IIa型纤维比例相似。这些结果表明，慢性阻塞性肺疾病患者的股外侧肌收缩特性得以保留。因此，慢性阻塞性肺疾病患者股四头肌力量的降低不能基于收缩装置的改变来解释。
