Longitudinal change in ultrasound-derived rectus femoris cross-sectional area in COPD

Abstract

Background: Skeletal muscle dysfunction is common in chronic obstructive pulmonary disease (COPD). Ultrasound-derived rectus femoris cross-sectional area (RFCSA) is a radiation free, non-invasive measure of muscle bulk that relates to quadriceps strength in people with COPD. However, there are limited longitudinal data for RFCSA, and it is not known whether longitudinal change in RFCSA reflects change in quadricep strength, exercise capacity, lower limb function or muscle mass. We aimed to quantify longitudinal change in ultrasound-derived RFCSA and assess its relationship with change in quadriceps maximal voluntary contraction (QMVC), incremental shuttle walk test (ISWT), five repetition sit-to-stand (5STS) and fat free mass (FFM) over 12 months in people with COPD.

Methods: We measured ultrasound-derived RFCSA, QMVC, ISWT, 5STS and FFM (measured by bioelectric impedance analysis) at baseline and 12 months in 169 people with stable COPD. Change was correlated using Pearsons or Spearman's coefficients.

Results: Baseline characteristics: Mean (sd) age 70 (9.4) years; FEV1 52.6 (18.8)% predicted. Over the course of 12 months mean (99% confidence interval) RFCSA change was −33.7mm2 (−62.6 to −4.9, p=0.003) representing a mean (sd) percentage change of −1.8% (33.5). There was a weak correlation between change in RFCSA and FFM (r=0.205 p=0.009), but not with change in QMVC, ISWT or 5STS.

Conclusion: There is a statistically significant decrease in ultrasound-derived RFCSA over 12 months in people with stable COPD, but this decrease does not correlate with change in quadriceps strength, exercise capacity, fat free mass nor lower limb function.