Abstract
Late Breaking Abstract - Diaphragm muscle density and function in chronic obstructive pulmonary disease
Background Studies of diaphragm muscle morphology and function in chronic obstructive pulmonary disease (COPD) have yielded conflicting results.
Objectives To investigate in vivo diaphragm muscle structure and function in COPD.
Methods Smokers 50-79 years old with and without spirometry-defined COPD underwent full-lung computed tomography (CT) at suspended maximal inspiration, pulmonary function testing according to European Respiratory Society standards, and symptom-limited incremental cardiopulmonary exercise testing on a cycle ergometer with a gastro-esophageal balloon catheter. Diaphragm muscle density and volume were measured by mapping the left hemi-diaphragm, and related to measures of trans-diaphragmatic pressure (Pdi), COPD assessment test (CAT) score, and breathlessness unpleasantness ratings at peak exercise. Regression techniques adjusted for age, gender, height, and post-bronchodilator forced expired volume in one second percent predicted (FEV1pp).
Results Fourteen participants completed the study to date. Independent of age, body size, and FEV1pp, lower diaphragm muscle density was associated with lower Pdi during resting inspiratory capacity maneuver (p=0.02), higher CAT score (p=0.002), and breathlessness unpleasantness at peak exercise (p<0.0001). Diaphragm muscle volume was associated with Pdi (p=0.006), but not CAT score or breathlessness at peak exercise (p>0.05). Results were similar with adjustment for diaphragm dome height.
Conclusion Among smokers with COPD, diaphragm muscle density assessed in vivo is associated with reduced diaphragm function, impaired health status, and breathlessness-limited exercise that is independent of spirometric disease severity.