Diagostic value of respiratory impedance measurements in elderly subjects.

Obstructive lung disease (OLD) is highly prevalent in elderly subjects but markedly under-diagnosed. Indeed, only 40-50% of hospitalized elderly patients are able to adequately perform spirometric tests. This study aimed to evaluate, in an acute-care geriatric hospital, the diagnostic value of measuring airway impedance (Zrs) by the forced oscillation technique (FOT) for: (1) identifying OLD and (2) identifying responders vs. non-responders to bronchodilators. Sixty-seven patients (aged 82+/-8 years) underwent consecutive measurement of Zrs and forced expiratory volumes before and after bronchodilators. Zrs was measured by FOT at frequencies of 4-30 Hz. Correlations, ROC curves and logistic regression models were established to determine the sensitivity (Se) and specificity (Sp) of Zrs in identifying OLD. Significant correlations were found between spirometric and Zrs measurements. The Zrs parameters yielding the best Se and Sp for detecting OLD were: Fn (resonant frequency; Se: 76%; Sp: 78%) and R0 (resistance extrapolated for a frequency of 0: Se: 76%; Sp: 74%). Using the logistic regression models, 76% of the patients were correctly classified as having OLD or not. Zrs was however not contributive in identifying responders to bronchodilators. Zrs measurements by FOT are contributive to the diagnosis of OLD in elderly hospitalized patients.