Theoretical and experimental studies of the diagnostic relevance and comparability of mechanical oscillation parameters

: The practical application of the forced oscillation technique for the analysis of the mechanics of respiration is hampered by the fact that the measured frequency-dependent impedance values R(f) and X(f) cannot be related directly to the parameters airway resistance Raw and pulmonary compliance CL. Furthermore, various derived oscillatory parameters are employed which are not directly comparable even with one another. In order to be able to estimate the diagnostic relevance and comparability of the impedance curves R(f) and X(f), their form-specific characteristics R = R(5)-R(20) and X(5), as also the equipment-specific parameters Ros (Siregnost FD5) and Rfo (custo vit), the relationships of these oscillatory parameters to Raw and CL were simulated in a structural model of the respiratory system, and tested in the real system. It was shown that already from frequencies of f greater than 10Hz upwards, R(f) no longer reacts to an increase in resistance in the peripheral region of the lung, and at 20 Hz indicates only the upper airway component of a global obstruction demonstrated body-plethysmographically with Raw. The diagnostic information on peripheral airway obstruction is contained in both components R(f) and X(f) of the respiratory impedance; with increasing obstruction and increasing frequency, it progressively reverts to the X(f) curve. Therefore, by including X(f) in the resistance evaluation for the parameters Ros and Rfo, the underevaluation of R(f) as compared with Raw can in part be compensated for, although an overe stimation at low Raw values with Ros and a large scatter of the Rfo values in the case of large Raw figures has to be accepted.(ABSTRACT TRUNCATED AT 250 WORDS)