• I Sipinková, E A Koller, C Buess, and J Kohl.
• Department of Physiology, University of Zurich, Switzerland.
• Crit. Care Med. 1994 Sep 1;22(9 Suppl):S66-70.

ObjectivesTo study the mechanical properties of the rabbit respiratory system during high-frequency oscillatory ventilation by means of mechanical respiratory impedance measurement and to characterize the changes in oscillation mechanics of the respiratory system occurring after bilateral vagotomy.DesignAcute experimental trial.SettingPhysiology laboratory.SubjectsTen adult rabbits (mean body weight 3.1 kg).Measurements And Main ResultsAnesthetized rabbits were exposed to short runs of high-frequency oscillatory ventilation, with stroke volumes of 5.0, 6.6, and 10.0 mL, applied at oscillation frequencies of 10, 15, 20, and 25 Hz before and after vagotomy. Mechanical respiratory input impedance was determined from the pressure and flow signals simultaneously measured at the airway opening and analyzed in terms of its real and imaginary parts. (The real part of respiratory impedance characterizes the resistive property of the lungs and chest wall; the imaginary part of respiratory impedance characterizes the elastic and inertial properties of the lungs and chest wall.) At all stroke volumes and oscillation frequencies studied, vagotomy resulted in a decrease in the real part of respiratory impedance. After vagotomy, the real part of respiratory impedance was stroke volume-independent, and exhibited negative frequency dependency. Vagotomy also led to a decrease in the imaginary part of respiratory impedance, mainly at lower oscillation frequencies, and thus, to a higher resonant frequency of the respiratory system.ConclusionsMechanical respiratory impedance measurement proved to be a useful method to study the mechanical properties of the respiratory system during high-frequency oscillatory ventilation. The results suggest that vagally mediated reflex changes in respiratory system mechanics are associated with high-frequency oscillatory ventilation, depending on the ventilatory variables that are used.

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