Sonographic Assessment of Diaphragm Thickness and Its Effect on Inspiratory Muscles' Strength in Patients with Chronic Obstructive Pulmonary Disease

Objective: To assess diaphragm thickness and to assess its effect on inspiratory muscles’ strength in patients with chronic obstructive pulmonary disease (COPD).
Methods: Case-control study was conducted on 113 male patients with COPD compared to 114 age-matched non-COPD males. Spirometric indices, maximum inspiratory pressure (MIP%), maximum expiratory pressure (MEP%), 6-min walk distance (6MWD), PaO2, PaCO2, and ultrasound measurement of diaphragm thickness were performed for all participants. The studied COPD cases were classified according to the diaphragm muscle thickness into a group with normal diaphragm muscle thickness (thickness end expiration ≥1.8 mm) and a group with diaphragm muscle thinning (thickness end expiration <1.8 mm).
Results: Thickening fraction (TF) on right side, spirometric indices, MIP%, MEP%, were significantly lower in patients with COPD than in controls. Patients with diaphragm muscle thinning represented 11.5% of patients with COPD which represent 21.7% of cases with severe-to-very severe COPD. In patients with diaphragm muscle thinning, age, smoking index, and PaCO2 were significantly higher, whereas body mass index (BMI), TF bilaterally, forced expiratory volume (FEV)1%, MIP%, MEP%, 6MWD, and PaO2 were significantly lower than those with normal diaphragm muscle thickness. Additionally, TF and MIP% showed a significant negative correlation with age, smoking index, and PaCO2 and a significant positive correlation with FEV1, PaO2, BMI, and 6MWD. By multiple logistic regression analysis, the most significant factors relevant to the diaphragm muscle thinning were forced vital capacity (FVC)%, smoking index, forced expiratory flow rate at 25-75% of vital capacity (FEF)25%–75%, and FEV1%.
Conclusion: Thinning of the diaphragm was related to COPD severity, smoking index, and older age. Reduced inspiratory muscles’ strength (MIP%) was related to diaphragm thickness (TF), FEV1/FVC ratio, smoking index, and FVC%. Assessment of diaphragm thickness in COPD patients is recommended with early implementation to pulmonary rehabilitation program.