Longitudinal follow-up of quadriceps strength and function in a COPD cohort after 3 years

The Association between Fat-Free Mass and Exercise Test Outcomes in People with Chronic Obstructive Pulmonary Disease: A Systematic Review

People with chronic obstructive pulmonary disease (COPD) tend to have abnormally low levels of fat-free mass (FFM), which includes skeletal muscle mass as a central component. The purpose of this systematic review was to synthesise available evidence on the association between FFM and exercise test outcomes in COPD. MEDLINE, Cochrane Library, EMBASE, Web of Science, and Scopus were searched. Studies that evaluated exercise-related outcomes in relation to measures of FFM in COPD were included. Eighty-three studies, containing 18,770 (39% female) COPD participants, were included. Considerable heterogeneity was identified in the ways that FFM and exercise test outcomes were assessed; however, higher levels of FFM were generally associated with greater peak exercise capacity. This association was stronger for some exercise test outcomes (e.g. peak rate of oxygen consumption during incremental cycle exercise testing) than others (e.g. six-minute walking distance). This review identified heterogeneity in the methods used for measuring FFM and exercise capacity. There was, in general, a positive association between FFM and exercise capacity in COPD. There was also an identified lack of studies investigating associations between FFM and temporal physiological and perceptual responses to exercise. This review highlights the significance of FFM as a determinant of exercise capacity in COPD.

Ultrasound Evaluation of the Quadriceps Muscle Contractile Index in Patients with Stable Chronic Obstructive Pulmonary Disease: Relationships with Clinical Symptoms, Disease Severity and Diaphragm Contractility

Rationale

Chronic obstructive pulmonary disease (COPD) is associated with changes in the composition and function of peripheral and respiratory muscles, which can negatively impact quality of life. Ultrasonography can provide a non-invasive evaluation of the integrity of both peripheral muscles and diaphragm, but its use in patients with COPD is still being investigated. We aimed at evaluating the relationship between quadriceps size, using ultrasonography and symptoms, lung function and diaphragm contractility in a cohort of patients with COPD.

Methods

COPD patients were prospectively recruited and ultrasonography of the dominant quadriceps and of the diaphragm was performed. Quadriceps size was evaluated using three measurements: 1) cross-sectional area of the rectus femoris (Qcsa), 2) thickness (Qthick) and 3) contractile index (Qci), defined as the ratio of quadriceps thickness/total anterior thigh thickness. Diaphragm contractility was evaluated using thickening fraction (TFdi). Clinical characteristics and number of moderate-to-severe exacerbations in the previous year were retrieved from medical files. Dyspnea (mMRC scale) and disease impact on health status (COPD Assessment Test (CAT)) were measured at inclusion. Fat-free mass index (FFMI) was assessed using bioelectrical impedance.

Results

Forty patients were recruited (20 males, mean age and FEV₁ 66±6 years and 49±17%predicted, respectively). Mean Qcsa, Qthick and Qci were 336±145 mm², 1.55±0.53 cm and 64±16%, respectively, and mean TFdi was 91±36%. Qci was significantly correlated with FFMI (rho=0.59, p=0.001), TFdi (rho=0.41, p=0.008), FEV₁ (rho=0.43, p=0.001) but not with age (rho=0.18, p=0.28). Qci was significantly correlated to CAT score (rho=−0.47, p=0.002), even when controlled for FEV₁, and was lower in patients with an mMRC score ≥2 (55±15 vs 70±14%, p=0.002). Qcsa and Qci were significantly lower in patients with frequent exacerbations. In a multiple linear regression analysis that included age, gender, FFMI, FEV₁ and TFdi, only FFMI and TFdi were found to be significantly related to lower Qci values.

Conclusion

In patients with COPD, ultrasound evaluation of the quadriceps contractile index is feasible and related to disease severity, clinical symptoms, exacerbation history and diaphragm contractility. As such, it may provide a novel tool for the evaluation of the severity and burden of the disease in this population. Further studies are required to better delineate its potential role as a prognostic marker in this population.