Parasternal intercostal muscle ultrasound measurements correlate with disease severity in chronic obstructive pulmonary disease: a pilot study

Abstract

Background: Chronic obstructive pulmonary disease (COPD) is a systemic condition, resulting in changes in muscle size, function and quality. Computed tomography (CT) measured intercostal mass correlates with COPD severity defined by forced expiratory volume (FEV1). Aims and Objectives: This pilot study aimed to 1) assess the reliability of ultrasound (US) measures of intercostal muscle quantity (thickness) and quality (echogenicity) using quantitative grayscale analysis; 2) determine the validity of US measures against COPD disease severity. We hypothesized that US measurement of intercostal muscles is reliable and correlates to COPD severity. Methods: 20 stable patients with COPD underwent US by a single operator with repeated measures of 2nd and 3rd parasternal intercostal muscle, quadriceps and diaphragm thickness and muscle echogenicity. Relationships between COPD severity and US parameters were analysed. Results: Intraclass correlation (ICC) for intra-rater measurement of US intercostal thickness ranged between 0.87-0.97 depending on side and level with ICC 0.63-0.91 for echogenicity. There was a moderate linear relationship between intercostal thickness and FEV1 (r = 0.58), quadriceps thickness (r = 0.42) and diaphragm thickness (r = 0.33). There was a negative correlation between intercostal thickness and higher echogenicity scores (indicating greater muscle deterioration) (r = -0.5). Conclusions: Intra-rater reliability of parasternal intercostal muscles US in COPD is good to excellent. Lower intercostal muscle quantity and deterioration in muscle quality (as measured by echogenicity) is related to higher spirometry-defined disease severity.