Background: Chronic obstructive pulmonary disease (COPD) and bronchial asthma lead to chronic airflow limitation, which is supposed to alter the position and shape of the diaphragm due to increased lung volume with subsequent impairment of diaphragm contractility.
Objective: To evaluate and compare diaphragm thickness (DT) using ultrasonography in COPD patients and asthma patients.
Methodology: A participants were subjected to measurements of spirometric indices and assessment of DT using ultrasound.
Results: The DT at residual volume (DT-RV) was significantly decreased in COPD patients than either asthma or control groups. The DT at total lung capacity (DT-TLC) and diaphragm thickness fraction (DTF %) were significantly reduced in COPD group than both asthma and control groups, and in asthma group than control group. In asthma group, the DTF% was inversely correlated with smoking index and asthma duration, and positively correlated with FEF25-75%. In COPD group, the DTF% was positively correlated with FEV₁/FVC ratio and FEV₁%. The DTF% cutoff 24.5% can discriminate between normal diaphragm function and diaphragm dysfunction (DD) in asthmatic patients with 74% sensitivity, 62.4% specificity, 67.3% PPV and 69.3% NPV. In COPD, the DTF% cutoff 23.7% can discriminate between normal diaphragm function and DD with 85% sensitivity, 66.3% specificity, 73.2% PPV and 79.3% NPV. DD was detected in 25% of asthmatic patients and 37% of COPD patients. The important  predictive factors of DD in asthmatic patients were FVC%, age, FEV₁% and asthma duration, while in COPD it were COPD duration, age, smoking index, FEV₁% and body mass index (BMI).
Conclusion: DD is prevalent among both COPD and asthmatic patients. The DT and contractility were significantly declined in both asthmatic and COPD patients compared to healthy subjects, and in COPD patients than asthma patients.