Correlation between peripheral skeletal muscle functions and the stable phase of COPD in older patients

To establish normal values for detection indexes of peripheral skeletal muscle dysfunction (quadriceps femoris) of healthy older subjects, and investigate the functional status of the peripheral skeletal muscle of patients with stable phase COPD.

Patients with stable phase COPD and healthy subjects of similar age were included. The assessments of strength and myoelectricity of the quadriceps femoris were recorded. The twitch tension of the quadriceps femoris (TwQ), quadriceps maximum voluntary contraction (QMVC), and endurance time (Tf) were measured. The multiple-parameter malnutrition index (MNI) was used for overall evaluation of the nutritional status of patients. The femoral muscle volume was estimated. All subjects were subjected to a routine pulmonary function test including indexes such as FEV1, FVC, FEV1/FVC (%), and PEF. Enzyme-linked immunoassay (ELISA) was used to measure the levels of myostatin, tumor necrosis factor-α, TNF-like apoptosis-inducing factor (TWEAK), surface active protein D (SPD), C-reactive protein (CRP), interleukin (IL)-1β, and IL-6. The cell immunohistochemical method was used to detect the expression of nuclear factor Kappa B (NF-κB).

There were significant differences in body weight, BMI, femoral muscle volume, and physical activity scores between the two groups (p<0.01). The MNI of patients in the COPD group was significantly higher than that in the control group (p<0.01). The QMVC of 51 male and 16 female patients decreased. All eight tested cytokines increased in the COPD group but there were only significant differences in four cytokines (p<0.05).

Chronic systemic inflammation is a major risk factor of skeletal muscle dysfunction (SMD) in COPD patients. The levels of SPD, myostatin, TWEAK, and TNF-α decreased significantly in COPD patients.