USE OF TRANSFER IMPEDANCE MEASUREMENTS FOR CLINICAL-ASSESSMENT OF LUNG-MECHANICS

Respiratory transfer impedance (Z(tr)) measured using the forced oscil lation technique requires virtually no patient cooperation and provide s a noninvasive approach for acquiring data reflective of lung mechani cs. Also, model analysis of Z(tr) provides reliable estimates of separ ate airway and tissue properties (1), but only if data out to 64 Hz ar e acquired. The current study evaluated the clinical utility of Z(tr) from 1-80 Hz for assessing the degree and type of impaired lung functi on. Spirometry and Z(tr) measurements were made on 37 individuals: 11 healthy subjects and 26 patients with lung disease including chronic o bstructive pulmonary disease (CORD), asthma, lung cancer, and sarcoido sis. Over the entire patient group, 12 were also smokers. We first est ablished normal ranges for several Z(tr) features and model estimated mechanical properties. The CORD and smokers groups showed significant differences in portions of their Z(tr) spectra from that of the health y group. Key Z(tr) spectral features included R-0 the frequency at whi ch the real part of impedance is zero; and Re-4 the real part of imped ance at 4 Hz. The key model parameter was airway resistance, Raw. We f ound Raw, Re-4, and R-0 to be significantly elevated during disease (p < 0.0005) and to significantly decrease with bronchodilator therapy ( p < 0.025). Moreover, we found moderate to strong correlations between R-0, Raw, and Re-4 versus FVC and R-0 versus FEV1. After bronchodilat or, changes in R-0, Re-4, and Raw were correlated with changes in seve ral spirometric indices. The R-0 feature has not been previously evalu ated since it is typically above 32 Hz (well above 32 Hz in diseased i ndividuals) and not encompassed in previous clinical studies.