A Stable Blunt Costophrenic Angle in Healthy Subjects, Associated with Dysanapsis and Airflow Limitation

Objective: A blunt costophrenic (CP) angle in chest radiographs is known as a sign of pleural effusion, but is also observed in pulmonary emphysema. However, healthy young adult subjects with a blunt CP angle were often encountered in company annual medical examinations. The goal of the study was to evaluate radiographic measurements, spirometry, and cough symptoms in such subjects with a stable blunt CP angle obtained in a company medical check to clarify the underlining condition. Methods: Radiographic measurements were made for the diameter of the main bronchus (MB), the tracheal width (TR), and the lung area (LA) estimated from the product of the height of the right lung and internal chest diameter in posteroanterior chest radiographs. The MB/LA and TR/LA ratios were calculated as markers of dysanapsis. An interview was performed to obtain information on cough symptoms. Results: The MB/LA and TR/LA ratios were both significantly lower in subjects with a blunt CP angle than in controls without blunt CP angles. Spirometry in the subjects with blunt CP angles indicated that 57.2% of parameters, including FEF25-75%, FEF75%, FEF50%, PEF, and FEV1/FVC, were subnormal and 84.1% of the subjects had a concave maximal expiratory flow-volume curve. These spirometric findings suggest the presence of airflow limitation involving the small airways. In correlation analyses, the MB/LA ratio was significantly associated with FEF25-75%/FVC, PEF, and FEF50%; and the TR/LA ratio was positively correlated with FEF25-75%/FVC and FEF50%. In interviews, 62.1% of subjects with a blunt CP angles stated that they had experienced cough symptoms in recent years or in the past. Conclusion: A stable blunt CP angle is associated with dysanapsis and airflow limitation. These changes may explain the high rate of cough among subjects with a stable blunt CP angle.