Correlation between diaphragm thickness and respiratory synergist muscle activity according to severity of chronic obstructive pulmonary disease

[Purpose] This study aims to analyze the effect that moderate to severe chronic obstructive pulmonary disease (COPD) has on the respiratory synergist muscles. The results will provide basic data that can be used in the clinical management of COPD. [Subjects and Methods] The subjects in the study were 47 male patients with COPD between 55 and 70 years old who were treated in a medical institution located in Jeollanam-do Province, South Korea, from October 2015 to December 2016. Measurements were analyzed to determine the correlation between the diaphragm thickness and the respiratory synergist muscle activity in patients with mild COPD. [Results] The results showed that there was a negative correlation between the diaphragm thickness and the sternocleidomastoid muscle and between the diaphragm thickness and the scalene muscle; however, there was a positive correlation between the diaphragm thickness and the external intercostal. For patients with severe COPD, negative correlations were found between the diaphragm thickness and the sternocleidomastoid muscle and between the diaphragm thickness and the scalene muscle. [Conclusion] The mechanical deformation of the thoracic cage caused by severe COPD reduces the lung capacity of patients and, thus, increases the difficulty in breathing. As the disease worsens, the patients tend to maintain ventilation using the respiratory synergist muscles. Thus, offering early and aggressive treatment and a respiration rehabilitation program to patients with COPD can help to reduce the actions of the respiratory synergist muscles to ensure normal breathing.