[The diagnostic utility of the Macao predictive values of impulse oscillometry for chronic obstructive pulmonary disease in patients over 45 years old].

Objective: To investigate the clinical use of Macao predictive values of impulse oscillometry(IOS) for chronic obstructive pulmonary disease (COPD) in patients aged over 45 years.

Methods: We measured lung impedance with IOS and spirometry in healthy subjects (n=168) and patients with COPD (n=281) aging over 45 years. The spirometric parameters were compared with those of IOS calculated by Macao predictive equations with Lechtenboerger equations.

Results: Respiratory impedance (Zrs), respiratory resistance at 5 Hz (R5), R5-R20 in female COPD group were (0.72±0.28), (0.63±0.23)and(0.23±0.16) kPa·L(-1)·s(-1), respectively, and Fres was (22±7)Hz; while in male group, the value of each parameters was (0.56±0.21), (0.50±0.17) and(0.18±0.12) kPa·L(-1)·s(-1), Fres was(21±7)Hz, which were all greater than that of the healthy group(t value was 5.05, 4.30, 5.10, 6.05 and 8.27, 6.62, 12.68, 14.59, respectively; P value were all<0.01). Reactance at 5 Hz(X5) in the COPD group[(-0.30±0.21) kPa·L(-1)·s(-1) in female, (-0.26±0.16) kPa·L(-1)·s(-1) in male] was significantly lower than that in the healthy group[female group: X5=(-0.16±0.06) kPa·L(-1)·s(-1,) t value was -5.38; male group: X5=(-0.10±0.05) kPa·L(-1)·s(-1,) t value was -11.96, P value were all<0.01]. Zrs, R5, R5-R20 and Fres were negatively correlated with parameters (FEV1/FVC, FEV1%Pre) of spirometry, while X5 was positively correlated with them. Compared with the ROC areas under the curve(AUC), the AUC of Zrs(A/P2) (0.786 in female, 0.773 in male) was same as that of Zrs(A)(0.744 in female, 0.764 in male; χ(2) value was 4.96, 0.89, respectively, P value were all >0.05), the AUC of R5(A/P2)(0.754 in female, 0.741 in male) was larger than that of R5(A/P1) (both were 0.716; χ(2) value was 4.24, 6.38, respectively, P value were all <0.05). The AUC of X5(P2-A) was larger than that of X5(P1-A) in the male group, and it was same as in the female group. The first two AUC of IOS parameters were Fres and R5-R20. In the 2 groups, when Zrs (A/P2)% was larger than 130, R5(A/P2)% was larger than 130, X5(P2-A)was larger than 0.1, Fres was larger than 15 in male, 20 in female, their each Youden's index was 0.463, 0.398, 0.662 and 0.594, each accuracy was 84%, 71%, 81% and 82%, which were all greater than that of Lechtenboerger equations(66%, 63%, 80% and 50%).

Conclusion: There are good correlations between spirometry and respiratory impendance measured by IOS in the diagnosis of COPD. The Macao predictive equations have higher sensitivity and specificity for diagnosing COPD.