Respiratory system reactance as an indicator of the intrathoracic airway response to methacholine in children
✍ Scribed by N. Bouaziz; C. Beyaert; R. Gauthier; P. Monin; R. Peslin; F. Marchal
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 749 KB
- Volume
- 22
- Category
- Article
- ISSN
- 8755-6863
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✦ Synopsis
The upper airways may contribute to increases in airway resistance in response to a bronchial challenge, and thus decrease the specificity of such challenge tests to diagnose airway hyperresponsiveness when forced oscillation techniques are used to evaluate changes in respiratory system resistance (&). A concomitent decrease in respiratory system reactance ( X, ) may indicate a change in the intrathoracic airways and/or lung parenchyma, provided that extrathoracic airway wall motion is prevented. To test the value of X , in the evaluation of bronchial hyperresponsiveness, we studied the respiratory impedance response to methacholine in 38 children with a history of asthma (aged 6-14.5 years), and compared the results to changes in the forced expiratory volume in one second (FEV1). R, and X , were measured by the forced oscillation technique with pseudorandom (11 subjects) or sinusoidal (27 subjects) pressure variations applied around the child's head to minimize upper airway wall motion. Changes in R, and in X, at 12 Hz (R,12, Xm12) correlated significantly with changes in FEV, (P < 0.005).
A decrease in FEV, 2 20% was observed in 23 subjects. When these 23 subjects were compared with the 15 children who did not show significant changes in FEV1, the responding group had larger mean ?SEM changes in R, (116.0 L 13.2% vs 60.4 ? 11.4%, P < 0.006) and in X , (-2.1 ? 0.4 hPa slL vs -0.9 5 0.3 hPadL, P < 0.03) than the nonresponders. The receiver operating characteristics (ROC) curve analysis was used to assess the diagnostic value, i.e., specificity and sensitivity, of different levels of change in R, and X,, with reference to FEV,. The overall incidence of false results was similar for R, and X , . The optimum diagnostic value for R, was a 70% increase, which corresponded to a sensitivity of 87% and a specificity of 67%. For X , the optimum decision level was -1 hPas/L, corresponding to a sensitivity of 70% and a specificity of 80%. It is concluded that X, may improve the specificity of the forced oscillation technique in interpreting the airway response to methacholine. This may be of particular interest in young children unable to perform forced expirations.