Measuring intra-subject changes in respiratory mechanics by oscillometry: impedance versus admittance

Extract

Recent state-of-the-art reviews [1, 2] and research [3] have pointed out the potential interest of oscillometry for noninvasively characterising lung mechanics from the relationship between oscillatory pressure (P) and flow (V′) at different frequencies. Two magnitudes have usually represented this relationship: resistance (R) and reactance (X), which are the real and imaginary parts of respiratory impedance (Z=R+j·X). Clinical [1, 2] and modelling data [4] show that both R and X depend on the interaction between resistances and compliances of central and peripheral airways and lung tissues. Even at the low oscillometry frequency of 5 Hz (which is a critical reference frequency for clinical studies [1, 2]), a simple interpretation of R and X is not possible [4].