[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.