Impact of chronic obstructive pulmonary disease severity on diaphragm muscle thickness

Abstract

BackgroundSonographic assessment of the diaphragm muscle thickness for disease progression in chronic obstructive pulmonary disease (COPD) patients was poorly evaluated. AimTo assess the impact of COPD severity on diaphragm muscle thickness measured by transthoracic ultrasound (TUS). MethodsCase-control study was conducted on 100 clinically stable male COPD patients and100 age-matched healthy subjects. Thickness of the diaphragm (TD) was measured by B- mode TUS. Measurements were taken on three different images to find the average static TD at residual volume (RV) and at total lung capacity (TLC). A thickness fraction (TF) was derived by subtracting the average thickness of the diaphragm at RV from the average thickness of the diaphragm at TLC/average thickness of the diaphragm at RV [TD at TLC-TD at RV/TD at RV]. COPD severity was measured by spirometry. Moreover, partial pressure of oxygen (PaO2) and partial pressure of carbon dioxide (PaCO2) were measured. ResultsThe right and left TF were significantly lower in COPD group than control group. All static right and left TD indices didn't shows any significant difference between COPD group and control group (p>0.05). The right and left TF were significantly decreased through progression of COPD (mild, moderate, severe and very-severe grades) (p=0.020, 0.002 respectively). TD at RV bilaterally were negatively correlated with the smoking index, also the left TD at TLC was negatively correlated with the smoking index and forced vital capacity (FVC%). The right and left TF were positively correlated with body mass index (BMI), forced expiratory volume in first second (FEV1%), FEV1/FVC ratio, and PaO2, while it was negatively correlated with PaCO2. ConclusionThe static TD measured at RV and at TLC are preserved in COPD. The TF bilaterally was significantly decreased in COPD group and is decreased with increasing severity of COPD. The negative correlation of TF and PaCO2 indicates that the diaphragm dysfunction is the main contributor to neuromuscular respiratory failure in COPD patients.