The product of trunk muscle area and density on the CT image is a good indicator of energy expenditure in patients with or at risk for COPD

Abstract

Background: Physical inactivity due to cachexia and muscle wasting is well recognized as a sign of poor prognosis in chronic obstructive pulmonary disease (COPD). However, there have been no reports on the relationship between trunk muscle measurements and energy expenditure parameters, such as the total energy expenditure (TEE) and physical activity level (PAL), in COPD. In this study, we investigated the associations of computed tomography (CT)-derived muscle area and density measurements with clinical parameters, including TEE and PAL, in patients with or at risk for COPD, and examined whether these muscle measurements serve as an indicator of TEE and PAL.

Methods: The study population consisted of 36 male patients with (n = 28, stage 1-4) and at risk for (n = 8) COPD aged over 50 years. TEE was measured by the doubly labeled water method, and PAL was calculated as the TEE/basal metabolic rate estimated by the indirect method. The cross-sectional areas and densities of the pectoralis muscles, rectus abdominis muscles, and erector spinae muscles were measured. We evaluated the relationship between these muscle measurements and clinical outcomes, including body composition, lung function, muscle strength, TEE, and PAL.

Results: All the muscle areas were significantly associated with TEE, severity of emphysema, and body composition indices such as body mass index, fat-free mass, and trunk muscle mass. All trunk muscle densities were correlated with PAL. The product of the rectus abdominis muscle area and density showed the highest association with TEE (r = 0.732) and PAL (r = 0.578). Several trunk muscle measurements showed significant correlations with maximal inspiratory and expiratory pressures, indicating their roles in respiration.

Conclusions: CT-derived measurements for trunk muscles are helpful in evaluating physical status and function in patients with or at risk for COPD. Particularly, trunk muscle evaluation may be a useful marker reflecting TEE and PAL.

Keywords: Chronic obstructive pulmonary disease; Computed tomography; Energy expenditure; Physical activity level; Trunk muscle.

Fig. 1

Representative computed tomographic images used to measure the cross-sectional areas of the trunk muscles. The pectoralis muscle (PM) (a), erector spinae muscle (ESM) (b), and the rectus abdominis muscle (RAM) (c) are shown in green

Fig. 2

The relationship between area and density of each muscle. Significant associations were observed between the two variables in the pectoralis muscle (a), rectus abdominis muscle (b), and erector spinae muscle (c). PMA pectoralis muscle area, PMD pectoralis muscle density, RAMA rectus abdominis muscle area, RAMD rectus abdominis muscle density, ESMA erector spinae muscle area, ESMD erector spinae muscle density

Fig. 3

Relationships among muscles (area or density): PMA and RAMA (a), PMA and ESMA (b), RAMA and ESMA (c), PMD and RAMD (d), PMD and ESMD (e), and RAMD and ESMD (f). In these comparisons, both areas and densities showed good correlations between the pectoralis and rectus abdominis muscles (a, d). PMA pectoralis muscle area, PMD pectoralis muscle density, RAMA rectus abdominis muscle area, RAMD rectus abdominis muscle density, ESMA erector spinae muscle area, ESMD erector spinae muscle density

Fig. 4

Relationships between PAL and the products of areas and densities of each muscle. PAL shows significant associations with PM product (a), RAM product (b), and ESM product (c). PM pectoralis muscle, RAM rectus abdominis muscle, ESMA erector spinae muscle, PAL physical activity level