Non-volitional assessment of skeletal muscle strength in patients with chronic obstructive pulmonary disease

Abstract

Background: Although quadriceps weakness is well recognised in chronic obstructive pulmonary disease (COPD), the aetiology remains unknown. In disabled patients the quadriceps is a particularly underused muscle and may not reflect skeletal muscle function as a whole. Loss of muscle function is likely to be equally distributed if the underlying pathology is a systemic abnormality. Conversely, if deconditioning and disuse are the principal aetiological factors, weakness would be most marked in the lower limb muscles. Methods: The non-volitional technique of supramaximal magnetic stimulation was used to assess twitch tensions of the adductor pollicis, quadriceps, and diaphragm muscles (TwAP, TwQ, and TwPdi) in 22 stable non-weight losing COPD patients and 18 elderly controls. Results: Mean (SD) TwQ tension was reduced in the COPD patients (7.1 (2.2) kg v 10.0 (2.7) kg; 95% confidence intervals (CI) -4.4 to -1.4; p<0.001). Neither TwAP nor TwPdi (when corrected for lung volume) differed significantly between patients and controls (mean (SD) TwAP 6.52 (1.90) N for COPD patients and 6.80 (1.99) N for controls (95% CI -1.5 to 0.97, p=0.65; TwPdi 23.0 (5.6) cm H 2 O for COPD patients and 23.5 (5.2) cm H 2 O for controls (95% CI -4.5 to 3.5, p=0.81). Conclusions: The strength of the adductor pollicis muscle (and the diaphragm) is normal in patients with stable COPD whereas quadriceps strength is substantially reduced. Disuse may be the principal factor in the development of skeletal muscle weakness in COPD, but a systemic process preferentially affecting the proximal muscles cannot be excluded.

Upper and Lower Limb Muscles in Patients With COPD: Similarities in Muscle Efficiency But Differences in Fatigue Resistance

“…34,35 One of the most common measures of muscle fatigue is the decline in maximum strength. 36 We found a greater drop in strength in the middle deltoid than in the quadriceps femoris (see Fig. 1), as did Gosker et al 18 ; however, the magnitude of that drop was less in our study, in both muscles: middle deltoid 20.6%, quadriceps femoris 10.6%, versus biceps brachii 42%, quadriceps femoris 28% in Gosker et al 18 The larger decline in strength in the study by Gosker et al 18 might be attributable to their more intense fatigue-inducing protocol (15 sequential maximal voluntary contractions at an angular velocity of 90°s), worse disease severity in their subjects (FEV 1 32 Ϯ 11% vs 46 Ϯ 10%), and lower fat-free mass and strength in the patients than in the control subjects.…”

Systemic manifestations and comorbidities of COPD

“…Even though peripheral muscle dysfunction is probably the most extensively studied systemic effect of COPD, its mechanisms are still poorly understood, but inactivity appears to be an important factor, as muscles that are active, such as the diaphragm and adductor pollicis, are not usually weak in contrast to inactive muscles, such as quadriceps and vastus lateralis [76]. Furthermore, the deltoid and diaphragm do not show the biopsy characteristics exhibited by the quadriceps [77].…”

Quadriceps wasting and physical inactivity in patients with COPD

“…The mechanisms involved in the development of skeletal muscle weakness in COPD are likely to be multifactorial, with systemic factors, such as oxidative stress [7], thought to interact with the key local factor of muscle inactivity [8,9] particularly in the lower limbs [10]. Objectively measured physical activity has been identified as a strong predictor of all-cause mortality in COPD [11], highlighting its importance in a ''downward disease spiral'' where progressive dyspnoea leads to reduced exercise capacity with subsequent muscle deconditioning and further inactivity [12].…”