Objective: To explore the correlation of respiratory resistance in stable COPD patients measured by broadband 3-dimensional impulse oscillometry (3D-IOS) and traditional pulmonary function test (PFT). To access the diagnostic value of 3D-IOS in COPD.
Methods: A total of 107 COPD patients and 61 healthy subjects as controls were chosen to collect and statistically analyze the data of R5, R5–R20, R20, X5 and Fres measured by broadband 3D-IOS and FEV1%pred, FVC%pred and FEV1/FVC by PFTs. The diagnostic value of broadband 3D-IOS parameters in COPD was evaluated by receiver operating characteristic curve (ROC). 3D-colored images used to show dynamic changes of respiratory resistance in COPD.
Results: The COPD group showed significant increases in R5, R20, R5–R20 and Fres, and a decrease in X5 (P < 0.05). With the increase of GOLD grade, R5, R5–R20 and Fres increased whereas X5 decreased (P < 0.05). Compared with FEV1%pred, FVC%pred and FEV1/FVC in the COPD group, R5, R5–R20 and Fres were negatively collated (P < 0.05), whereas X5 was positively collated (P < 0.01). R20 was uncorrelated with the traditional lung function parameters (P > 0.05). Fres and FEV1/FVC (r=− 0.467), and X5 and FEV1%pred (r=0.412) showed the strongest correlation. The AUC of R5, R5–R20, X5 and Fres was 0.7808, 0.7659, 0.8947 and 0.9095, respectively. Typical 3D-colored images of COPD displayed a green pattern in the inhalation phase and yellow–red–blue graduation in the expiration phase.
Conclusion: R5, R5-R20, X5 and Fres measured by broadband 3D-IOS can reflect the change of respiratory resistance in COPD. And they have good correlation with the traditional lung function parameters (FEV1%pred, FVC%pred, FEV1/FVC). Fres has the highest diagnostic accuracy. Comprehensive analysis of R5, R5–R20, Fres and X5 helps to determine the degree of respiratory obstruction in COPD. X5 and Fres can reflect changes in lung tissue compliance. 3D-colored images can visually show the change of respiratory resistance and reactance in COPD.
Keywords: 3-dimensional impulse oscillometry, respiratory resistance, pulmonary function test, chronic obstructive pulmonary disease