Factors associated with impairment of quadriceps muscle function in Chinese patients with chronic obstructive pulmonary disease

Abstract

Background: Quadriceps muscle dysfunction is well confirmed in chronic obstructive pulmonary disease (COPD) and reported to be related to a higher risk of mortality. Factors contributing to quadriceps dysfunction have been postulated, while not one alone could fully explain it and there are few reports on it in China. This study was aimed to investigate the severity of quadriceps dysfunction in patients with COPD, and to compare quadriceps muscle function in COPD and the healthy elderly.

Methods: Quadriceps strength and endurance capabilities were investigated in 71 COPD patients and 60 age-matched controls; predicted values for quadriceps strength and endurance were calculated using regression equations (incorporating age, gender, anthropometric measurements and physical activities), based on the data from controls. Potential parameters related to quadriceps dysfunction in COPD were identified by stepwise regression analysis.

Results: Mean values of quadriceps strength was 46% and endurance was 38% lower, in patients with COPD relative to controls. Gender, physical activities and anthropometric measurements were predictors to quadriceps function in the controls. While in COPD, forced expiratory volume in 1 second percentage of predicted value (FEV1% pred), nutritional depletion, gender and physical inactivity were identified as independent factors to quadriceps strength (R(2) = 0.72); FEV1%pred, thigh muscle mass, serum levels of tumor necrosis factor-alpha (TNF-α) and gender were correlated to quadriceps endurance variance, with each p<0.05.

Conclusion: Quadriceps strength and endurance capabilities are both substantially impaired in Chinese COPD patients, with strength most affected. For the controls, physical activity is most important for quadriceps function. While for COPD patients, quadriceps dysfunction is related to multiple factors, with airflow limitation, malnutrition and muscle disuse being the main ones.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. The functional test of quadriceps.

Figure 2. Simultaneous force and surface electromyography (SEMG) recordings during quadriceps maximal volitional contraction (QMVC) tests: the lines on the top channel represent the 3 consecutive volitional contraction forces; SEMG signals from vastus lateralis muscle (VL-M), rectus femoris muscle (RF-M) and vastus medialis muscle (VM-M) were shown in channel 2, 3 and 4, respectively; the number below the X axis represents the time (minute: second).

QMVC was about 25(Figure 2A) 40 kg in a male normal subject (Figure 2B).

Figure 3. Quadriceps endurance time test: the lines on the top channel represent the sustained isometric contraction at 60% value of quadriceps maximal volitional contraction (QMVC); surface electromyography (SEMG) from vastus lateralis muscle (VL-M), rectus femoris muscle (RF-M) and vastus medialis muscle (VM-M) were shown below the force line; the number below the X axis was the time (minutes: seconds).

The time to fatigue (QTf) in this figure was about 2 minutes and 20 seconds (140 seconds).