Objectives: To compare the change in oscillometric parameters after inhalation of a beta 2- agonist among healthy and asthmatic children aged 3 to 5 years old using impulseoscillometry.
Methods: The respiratory impedance at baseline and after 15 minutes of one dose of Salbutamol nebulization was measured with the impulse oscillometry(IOS) using the VIASYS (Healthcare ,Leibnizstr. Hoechberg Germany)at resistance at 5Hz and 20 HZ and reactance at 5HZ in 310 children aged 3-5years old. For the calculation of threshold or cutoff values, receiver operating characteristic (ROC) curves were drawn and was determined by the Youden index (J = max{sensitivity + specificity – 1}). Partial correlation study was done among multiple parameters to determine best positive correlation for diagnosis of asthma.
Results:
Fifty-six (18.1%) asthmatic subjects and 254 (81.9%) healthy subjects were able to complete the study. Mean percent (standard error of the mean) baseline pre bronchodilator indices for asthma were 1.21 ± 0.02 kPa/L/s for Z5Hz; 1.15 ± 0.02 kPa/L/s for R5Hz; 0.83 ± 0.01 kPa/L/s for R20Hz and -0.37 ± 0.01 kPa/L/s for X5Hz. In normal healthy subjects, the baseline mean values were 1.09 ± 0.01 kPa/L/s for Z5Hz; 1.04 ± 0.01 kPa/L/s for R5Hz; 0.79 ± 0.01 kPa/L/s for R20 Hz and -0.31 ± 0.01 kPa/L/s for X5Hz. In mean percent change initial values of asthmatics were -29.03% ± 0.73 for Z5Hz; -28.77% ± 0.81 for R5Hz; -22.96 % ± 0.97 for R20 Hz and 36.91 % ± 1.62 for X5Hz. Cut off values for bronchodilator response in diagnosing asthma using the percent change initial were as follows: -19.98% for Z5Hz with sensitivity of 100% and specificity of 96%; -21.25% for R5Hz with sensitivity of 95% and specificity of 98%; -13.96 % for R20 Hz with sensitivity of 93% and specificity of 78% and -24.25 % for X5Hz with sensitivity of 88% and specificity of 88%. Percent initial change of Z5Hz and R5Hz (r = 0.938, p<0.001) are significantly correlated.
Conclusion:
Values at baseline and postbronchodilator on the different IOS parameters were significantly higher in the asthmatic group. A post-bronchodilator change of -20% in Z5Hz and -21% in R5Hz from the initial has strong positive correlation for the diagnosis of asthma. The computed percent change post-bronchodilator for Z5Hz and R5Hz are the best parameters that showed better accuracy in terms of specificity and sensitivity in the diagnosis of asthma using impulse oscillometry in our population.