Mass of intercostal muscles associates with risk of multiple exacerbations in COPD.

Background: The potential role of decreased respiratory muscle mass, if any, in mediating the susceptibility to exacerbation in COPD patients has not been determined. We hypothesized that a decrease in respiratory muscle mass is associated with increased risk of multiple hospital admissions due to acute exacerbations of the disease.

Methods: Eligible cases and controls (n=20) were identified from records of our department's pulmonary clinic. Ten subjects diagnosed with COPD (males, 66+/-7yr, Body Mass Index (BMI)=26+/-4kg/m(2)) were identified as fragile patients. Fragility was defined as four or more admissions in the previous year due to severe exacerbations of the disease. Fragile patients were matched with 10 non-fragile controls, defined as COPD patients who had required only one admission due to exacerbation of the disease. Criteria for 1:1 matching included ethnicity, gender, age, BMI, degree of airflow obstruction (i.e., FEV(1)), comorbidity and chronic treatment. Multiple computed tomography (CT) scan slices were obtained to assess area and attenuation coefficients of multiple upper limb, thorax, abdomen and lower limb muscles.

Results: CSA of intercostal and abdominal muscles was significantly decreased in fragile COPD patients (right side intercostals, mean relative difference (MRD)=-14%, p=0.010; OR (95% CI)=2.2 (1.1-4.8), p=0.021; left side, MRD=-13%, p=0.007; OR=2.2 (1.1-4.5), p=0.027). CSA and attenuation coefficients of all other muscle compartments showed no statistical differences between the two study groups but showed the same trend. Strength of the inspiratory and expiratory muscles did not differ between the two study groups.

Conclusions: This study shows that the risk for multiple admissions due to a COPD exacerbation associates with a marked decrease in the CSA of the intercostal muscle compartment.