Expiratory and inspiratory resistance and reactance from respiratory oscillometry defining expiratory flow limitation in obstructive lung diseases

Background: Expiratory flow limitation (EFL) during tidal breathing and lung hyperinflation have been identified as major decisive factors for disease status, prognosis and response to therapy in obstructive lung diseases. Aim: To investigate the delta values between expiratory and inspiratory resistance and reactance, measured using respiratory oscillometry and its correlation with air trapping and symptoms in subjects with obstructive lung diseases. Methods: Four hundred and seventy-one subjects (96 with chronic obstructive pulmonary disease [COPD], 311 with asthma, 30 healthy smokers and 34 healthy subjects) were included. Spirometry, body plethysmography and respiratory oscillometry measurements were performed and the differences between the expiratory and inspiratory respiratory oscillometry values (as delta values) were calculated. Questionnaires regarding symptoms and quality of life were administered. Results: Patients with COPD and healthy smokers had an increased delta resistance at 5 Hz (R5) compared with patients with asthma (p < 0.0001 and p = 0.037, respectively) and healthy subjects (p = 0.0004 and p = 0.012, respectively). Patients with COPD also had higher values of Delta R5-R19 than healthy subjects (p = 0.0001) and patients with asthma (p < 0.0001). Delta reactance at 5 Hz (X5) was significantly more impaired in COPD patients than in asthma and healthy subjects (p < 0.0001 for all). There was a correlation between the ratio of residual volume and total lung capacity and Delta R5 (p = 0.0047; r = 0.32), Delta R5-R19 (p = 0.0002; r = 0.41) and Delta X5 (p < 0.0001; r = -0.44), for all subjects. Delta X5 correlated with symptoms in COPD, healthy smokers and patients with asthma. In addition, Delta R5 correlated with asthma symptoms. Conclusion: EFL was most prominent in parameters measuring peripheral resistance and reactance and correlated with air trapping and airway symptoms.