Diaphragm Morphology Assessed by Computed Tomography in Chronic Obstructive Pulmonary Disease

Rationale Chronic obstructive pulmonary disease (COPD) is associated with abnormal skeletal muscle morphology and function. Objectives We hypothesized that in vivo diaphragm muscle morphology assessed by computed tomography (CT) would be associated with COPD severity, exacerbations, health status, and exercise capacity. Methods The COPD Morphometry Study is a cross-sectional study that enrolled a clinical sample of smokers with COPD. Spirometry was performed and COPD severity defined according to guidelines. Three-dimensional left hemi-diaphragm morphology was segmented from contiguous axial CT images acquired at maximal inspiration, yielding quantitative measures of diaphragm CT density in Hounsfield units (HU), dome height, and muscle volume. Exacerbations prompting pharmacotherapy or hospitalization in the preceding 12-months and St. George's Respiratory Questionnaire for COPD (SGRQ-C) were assessed. Incremental symptom-limited cycle ergometry quantified peak oxygen uptake (VO2Peak). Associations were adjusted for age, gender, body height, body mass index, and smoking status. Results Among 65 smokers with COPD (75% male; [mean±SD] 56±26 pack-years; FEV1percent predicted 55±23%), mean diaphragm CT density was 3.1±10 HU, dome height was 5.2±1.3 cm, and muscle volume was 57±24 cm3. A 1-SD decrement in diaphragm CT density was associated with: 8.3% lower FEV1, 3.27-fold higher odds of exacerbation history, 9.7 point higher SGRQ-C, and 2.5 mL∕kg∕min lower VO2Peak. A 1-SD decrement in dome height was associated with 11% lower FEV1, and 1.3 mL∕kg∕min lower VO2Peak. No associations with diaphragm volume were observed. Conclusions CT-assessed diaphragm morphology was associated with COPD severity, exacerbations, impaired health status, and exercise intolerance. The mechanisms and functional impact of lower diaphragm CT density merit investigation.