Mild/Moderate Airflow Limitation in COPD Linked to Reduced Pectoralis Muscle

Patients with COPD with mild or moderate airflow limitation have a reduced pectoralis muscle area (PMA), suggesting that PMA measurement may be useful in COPD assessment, according to study findings published in Pulmonology.

Previous research shows patients with COPD and severe airflow limitation have reduced PMA, and that this is associated with mortality. Researchers for the current study sought to determine whether reduced PMA in patients with COPD is also associated with mild or moderate airflow limitation.

The analysis included 1352 patients with COPD from the Early Chronic Obstructive Pulmonary Disease study who returned for a second visit about 1 year after their first visit through December 2021. Eligible participants were aged 40 to 80 years, completed a questionnaire interview, and had complete spirometry and computed tomography (CT). The PMA was quantified in inspiratory CT at the aortic arch level based on predefined -50 and 90 Hounsfield unit (HU) attenuation ranges. Participants completed questionnaires regarding smoking status, environmental risk exposures, symptoms, exacerbations, and family history of respiratory diseases. Symptoms were assessed using the modified British Medical Research Council (mMRC) dyspnea scale and COPD Assessment Test (CAT) score.

Study participants were divided into 2 cohorts based on spirometry results: a normal spirometry cohort (n=667 patients; mean [SD] age, 58.0 [7.7] years; 60% male) and a spirometry-defined COPD cohort (n=685; mean age, 64.8 [7.1] years; 92% male). Global Initiative for Chronic Obstructive Lung Disease (GOLD) spirometry criteria were used as the basis for defining normal spirometry and COPD, with airflow limitation severity classified according to GOLD stages 1 to 4 criteria for levels of forced expiratory volume in 1 second (FEV₁) percent predicted.

After adjustment for confounding factors, the investigators found that PMA was monotonically lower with progressive airflow limitation severity in patients with COPD vs patients with normal spirometry (GOLD 1: β = -1.27; 95% CI, -2.41 to -0.14; P =.028; GOLD 2: β = -2.29; 95% CI, -3.48 to -1.11; P <.001; GOLD 3: β = -4.88; 95% CI, -6.94 to -2.83; P <.001; and GOLD 4: β = -6.47; 95% CI, -11.61 to -1.33; P =.014). The PMA was associated with age, sex, body mass index, and smoking index (all P <.05).

The PMA was negatively associated with the mMRC score in all patients (β = -0.005; 95% CI, -0.009 to -0.001; P =.026) and CAT score (β = -0.06; 95% CI, -0.09 to -0.02; P =.001) after adjustment for confounding factors.

The PMA had a positive association with prebronchodilator or postbronchodilator lung function indicators, including FEV₁, FEV₁ percent predicted, forced vital capacity (FVC), and FEV₁/FVC (all P <.05). A positive association also was observed regarding the pectoralis major muscle area and pectoralis minor muscle area.

The PMA had a negative association with emphysema (inspiratory low-attenuation area of the lung with attenuation values below -950 Hounsfield units: β = -0.07; 95% CI, -0.10 to -0.04; P <.001) and airflow trapping (expiratory low-attenuation area of the lung with attenuation values below -856 Hounsfield units: β = -0.24; 95% CI, -0.35 to -0.12; P <.001) in CT-quantitated imaging with adjustment for confounding variables.

At the 1-year follow-up after adjustment for confounding factors, the PMA was associated with a decreased annual decline in postbronchodilator FEV₁ percent predicted (β = 0.022; 95% CI, 0.008-0.035; P =.002). The PMA was not associated with the annual rate of exacerbations after 1 year.

Among several limitations, 3D software was used to measure the PMA but not the pectoralis muscle density. In addition, the follow-up was 1 year, which may not have been long enough to evaluate the association of the PMA with lung function decline and exacerbation. Also, the number of patients with GOLD stage 3 and 4 COPD was limited.

“To our knowledge, this is the first study to show a reduced PMA in patients with mild or moderate airflow limitation, thus expanding the knowledge base in this field,” stated the study authors. “Patients with mild or moderate airflow limitation have a reduced PMA, indicating not only worse lung function than individuals with normal spirometry but also extrapulmonary changes.”