Comparison of IOS parameters to aRIC respiratory system model parameters in normal and COPD adults

Abstract

Chronic Obstructive Pulmonary Disease (COPD) is an important cause of illness and death. Sensitive assessments of COPD may be obtained by Impulse Oscillometry (IOS) during resting breathing. The respiratory impedance measured by IOS is modeled well by the augmented RIC (aRIC) circuit with parameters R,I,Rp,Cp,Ce, representing central airway resistance and inertance, peripheral airway resistance and compliance, and extrathoracic compliance, respectively. IOS measurements (from 5 to 35 Hz) were obtained from ten normal adults and ten adults with varying degrees of COPD. The aRIC parameters were then derived by least-squares-optimal fitting to the IOS data. Using Mann-Whitney tests, the main IOS resistance and reactance parameters (R5, R5-R15, X5) and aRIC model parameters (R,Rp,I,Cp,Ce, Rp/C p) were analyzed to determine if the values for normal adults came from the same population as the COPD adults' values. For IOS R5, R5-R15, X5, the approximating z statistics were -6.47, -6.48, 6.46, respectively. For aRIC R,Rp,I,C p,Ce, Rp/Cp, the z statistics were -3.04, -4.31, 2.02, 6.34, 1.64, -6.46, respectively. At a 99% confidence level, all of these parameters, except aRIC I and Ce, were found to come from different distributions. Furthermore, we calculated the Pearson product-moment-correlation-coefficients between aRIC R,Rp,I,C p,Ce, 1/Cp,Rp/Cp, and IOS R5, R5-R15, X5, R 5-Rmin, Rmin. In COPD adults, we found very strong correlations between aRIC R and IOS Rmin (0.987), R p and X5 (-0.992), 1/Cp and R 5-Rmin (0.935), and Rp/Cp and X 5 (-0.962). We conclude that the aRIC model of respiratory impedance is as sensitive as IOS to lung function changes in COPD, and that certain aRIC parameters correlate well to IOS parameters used for clinical assessment of COPD. © 2010 Springer-Verlag.