###### Abstract  
High-frequency oscillatory ventilation (HFOV) is a type of mechanical ventilation with a protective potential characterized by a small tidal volume. Unfortunately, HFOV has limited monitoring of ventilation parameters and mechanical parameters of the respiratory system, which makes it difficult to adjust the continuous distension pressure (CDP) according to the individual patient's airway status. Airway resistance \(R_{\text{sw}}\) is one of the important parameters describing the mechanics of the respiratory system. The aim of the presented study was to verify in vitro whether the resistance of the respiratory system \(R_{\text{ss}}\) can be reliably determined during HFOV to evaluate \(R_{\text{sw}}\) in pediatric and adult patients. An experiment was performed with a 3100B high-frequency oscillator, a physical model of the respiratory system, and a pressure and flow measurement system. The physical model with different combinations of resistance and compliance was ventilated during the experiment. The resistance \(R_{\text{ss}}\) was calculated from the impedance of the physical model, which was determined from the spectral density of the pressure at airway opening and the spectral cross-density of the gas flow and pressure at airway opening. \(R_{\text{ss}}\) of the model increased with an added resistor and did not change significantly with a change in compliance. The method is feasible for monitoring respiratory system resistance during HFOV and has the potential to optimize CDP settings during HFOV in clinical practice. high-frequency oscillatory ventilation; continuous distending pressure; respiratory system resistance; rigid respiratory system model; forced oscillation technique +
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or impedance analysis of the respiratory system [11], can lead to optimization of HFOV settings. The results of previous studies conducted with HFOV may have been influenced by settings that were not sufficiently individualized to the needs of individual patients [12; 13]. Currently, there is no unified approach on how to properly set up CDP with respect to the respiratory status of individual patients. Airway resistance \(R_{\text{aw}}\) is one of the important parameters describing the mechanics of the respiratory system. Besides tissue resistance, airway resistance \(R_{\text{aw}}\) is a substantial part of respiratory system resistance \(R_{\text{rs}}\). Elevated \(R_{\text{aw}}\) can lead to air trapping and hyperinflation, which can result in pulmonary barotraum [14]. \(R_{\text{aw}}\) depends on lung volume [15; 16], which is directly related to the CDP value [17]. Both ventilation at low lung volumes (CDP is too low for the patient) and ventilation at high lung volumes (CDP is too high) lead to an increase in \(R_{\text{aw}}\). Moreover, the increase in resistance at low lung volumes is accompanied by a significant increase in peripheral resistance, which can account for 15% of \(R_{\text{aw}}\). The contribution of peripheral resistance to \(R_{\text{aw}}\) is otherwise negligible [15]. However, the possibilities for monitoring ventilation parameters are small for HFOV. The high-frequency oscillatory ventilators 3100A and 3100B (Vyaire Medical, Mettawa, IL, USA) also lack monitoring of respiratory system mechanics, such as \(R_{\text{aw}}\). The 3100B ventilator, designed for adult patients, was used in this study. The forced oscillation technique (FOT) can be used to evaluate the mechanics of the respiratory system including total respiratory system resistance \(R_{\text{rs}}\)[18; 19]. In FOT, pressure oscillations with typical frequency \(f=5\) Hz are applied at the airway opening and \(R_{\text{rs}}\) is assessed from the induced flow. Pressure oscillations at 5 Hz can penetrate the peripheral airways and detect changes in resistance in this region of the lung, allowing the assessment of \(R_{\text{rs}}\)[18]. In a conventional FOT configuration, an external tool with an oscillator is used to generate high-frequency oscillations.