Comparative evaluation of impulse oscillometry and a monofrequency forced oscillation technique in clinically healthy calves undergoing bronchochallenges.

Multifrequency impulse oscillometry (IOS) was compared with a monofrequency forced oscillation technique (MFO) in calves undergoing experimentally induced bronchoconstriction and subsequent bronchodilatation. The dynamic lung compliance (Cdyn) was also measured by conventional methods. For each test, the baseline mean and the responses to saline, a bronchoconstrictive agent (carbachol) and a bronchodilator (fenoterolhydrobromide) were calculated. Using the IOS, the information was markedly frequency-dependent. The resistance (R) and the magnitude of respiratory impedance (Z) were only sensitive at 5 Hz, leading to negative frequency dependence of these parameters as an indicator of peripheral airway obstruction. A high sensitivity for reactance (X) and phase angle phi values was observed between 5 and 20 Hz. For MFO (10 Hz), the parameters Ros (which includes resistive and capacitive components of the respiratory system), phase shift (psi), and the oscillatory derived compliance of the respiratory system (Crs) were of the greatest clinical potential. Crs showed a significant coefficient of linear correlation (r = 0.88, P < 0.001) with Cdyn. At the 10 Hz test frequency similar results were observed with MFO and IOS, suggesting that for healthy calves the measurement effect of an impulse is not significant. With respect to peripheral airway calibre, a test frequency less than 10 Hz appeared to be most sensitive and least variable.