Scaling skeletal muscle function to mass in patients with moderate-to-severe COPD

Abstract

Skeletal muscle performance and muscle mass are commonly reduced in patients with advanced chronic obstructive pulmonary disease (COPD). It is currently unclear, however, whether negative changes in muscle structure and function are proportionately related to each other in these patients. In a cross-sectional study, 39 patients (post-bronchodilator FEV1=49.7+/-15.5% pred) and 17 controls were submitted to knee isokinetic dynamometry [peak torque (PT), isometric strength (IS), and total work (TW)] and dual energy X-ray absorptiometry for the evaluation of leg muscle mass (LMM). Muscle function (F) was normalised for LMM by using ratio standards (F.LMM-1), power function ratios (F.LMM-b, where b is usually not equal 1), and analysis of covariance (ANCOVA). Patients with COPD presented with reduced PT, IS, TW, and LMM as compared to controls: there were significant linear correlations among these variables in both groups (P<0.05). Ratio standards of PT.LMM-1 and TW.LMM-1 were, on average, 14% lower in patients than controls (P<0.01). The coefficients for allometric correction of IS and TW were significantly higher in patients as compared to controls (0.975 vs. 0.603 and 1.471 vs. 0.824, respectively, P<0.05), i.e. more LMM was needed to generate a given functional output in patients than normal subjects. In addition, adjusted means of muscle function variables by ANCOVA were 11-18% lower for patients than controls with LMM as the covariate (P<0.05). We conclude that factors other than simple atrophy (i.e. mass-independent mechanisms) might play a role in explaining the COPD-related skeletal muscle dysfunction.

An Official American Thoracic Society/European Respiratory Society Statement: Update on Limb Muscle Dysfunction in Chronic Obstructive Pulmonary Disease

“…The latter method is easier and less invasive than the former but also more difficult to control, as it relies on patient collaboration. The exercise condition can be based on isometric contractions with maintenance of muscle length (258,298,483), on a dynamic contractions to shorten the muscle against a fixed load (concentric contractions) (243,256,257), or on variable loads but with constant angular speed (isokinetic) (193,487). Isometric and concentric contractions are physiological maneuvers that can be easily implemented at low cost but with a drawback of between-test variability and reduced sensitivity.…”

Deficits in Muscle Strength, Mass, Quality, and Mobility in People With Chronic Obstructive Pulmonary Disease

“…However, recent studies suggest that deficits in muscle mass do not entirely explain the reduction of muscle strength observed in COPD patients. 5 Thus, it is possible that muscle quality could partially explain strength deficits in COPD.…”

Métodos de avaliação da fadigabilidade muscular periférica e seus determinantes energético-metabólicos na DPOC

“…These changes increase the contribution of the anaerobic system to the generation of energy, resulting in early lactacidemia. (30) In summary, the association of abnormalities in peripheral muscle structure, bioenergy and function results in significant peripheral muscle tional ability and motivation of the patient, can generate contractions using submaximal activation. (31,32) However, due to its user-friendliness, the use of verbal encouragement and the experience of the technician, little variability has been described in MVC.…”

“…(36) Typically, in comparison with healthy controls, COPD patients were found to present lower isometric torque, lower isokinetic torque and lower total work. (30,37) …”

“…In order to assess strength, lower angular velocities, typically 60-90°/s, are recommended. (34) In order to assess endurance, the most widely used angular velocities are 180°/s (30) and 300°/s. (7,34) Greater torque is generated when low angular velocities are applied.…”