scholarly journals Assessment of Respiratory System Resistance during High-Frequency Oscillatory Ventilation Based on In Vitro Experiment

2021 ◽  
Vol 11 (23) ◽  
pp. 11279
Author(s):  
Jan Matejka ◽  
Martin Rozanek ◽  
Jakub Rafl
Keyword(s):  
Physical Model ◽  
Respiratory System ◽  
High Frequency ◽  
Gas Flow ◽  
High Frequency Oscillatory Ventilation ◽  
Oscillatory Ventilation ◽  
Airway Opening ◽  
Respiratory System Resistance ◽  
High Frequency Oscillatory

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 Raw 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 Rrs can be reliably determined during HFOV to evaluate Raw 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 Rrs 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. Rrs 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.

scholarly journals In Vitro Estimation of Relative Compliance during High-Frequency Oscillatory Ventilation

2021 ◽  
Vol 11 (3) ◽  
pp. 899
Author(s):  
Jan Matejka ◽  
Martin Rozanek ◽  
Jakub Rafl ◽  
Petr Kudrna ◽  
Karel Roubik
Keyword(s):  
Physical Model ◽  
Respiratory System ◽  
High Frequency ◽  
High Frequency Oscillatory Ventilation ◽  
Opening Pressure ◽  
Respiratory System Mechanics ◽  
Oscillatory Ventilation ◽  
Airway Opening ◽  
High Frequency Oscillatory

High-frequency oscillatory ventilation (HFOV), which uses a small tidal volume and a high respiratory rate, is considered a type of protective lung ventilation that can be beneficial for certain patients. A disadvantage of HFOV is its limited monitoring of lung mechanics, which complicates its settings and optimal adjustment. Recent studies have shown that respiratory system reactance (Xrs) could be a promising parameter in the evaluation of respiratory system mechanics in HFOV. The aim of this study was to verify in vitro that a change in respiratory system mechanics during HFOV can be monitored by evaluating Xrs. We built an experimental system consisting of a 3100B high-frequency oscillatory ventilator, a physical model of the respiratory system with constant compliance, and a system for pressure and flow measurements. During the experiment, models of different constant compliance were connected to HFOV, and Xrs was derived from the impedance of the physical model that was calculated from the spectral density of airway opening pressure and spectral cross-power density of gas flow and airway opening pressure. The calculated Xrs changed with the change of compliance of the physical model of the respiratory system. This method enabled monitoring of the trend in the respiratory system compliance during HFOV, and has the potential to optimize the mean pressure setting in HFOV in clinical practice.

scholarly journals High-frequency oscillatory ventilation in neonatal RDS: initial volume optimization and respiratory mechanics

1998 ◽  
Vol 84 (4) ◽  
pp. 1174-1177 ◽  
Author(s):  
Masendu Kalenga ◽  
Oreste Battisti ◽  
Anne François ◽  
Jean-Paul Langhendries ◽  
Dale R. Gerstmann ◽  
...  
Keyword(s):  
Respiratory System ◽  
Lung Volume ◽  
High Frequency ◽  
Distress Syndrome ◽  
Respiratory Mechanics ◽  
High Frequency Oscillatory Ventilation ◽  
Oscillatory Ventilation ◽  
Respiratory System Resistance ◽  
High Frequency Oscillatory ◽  
Good Oxygenation

To determine whether initial lung volume optimization influences respiratory mechanics, which could indicate the achievement of optimal volume, we studied 17 premature infants with respiratory distress syndrome (RDS) assisted by high-frequency oscillatory ventilation. The continuous distending pressure (CDP) was increased stepwise from 6–8 cmH2O up to optimal CDP (OCDP), i.e., that allowing good oxygenation with the lowest inspired O2 fraction. Respiratory system compliance (Crs) and resistance were concomitantly measured. Mean OCDP was 16.5 ± 1.2 cmH2O. Inspired O2 fraction could be reduced from an initial level of 0.73 ± 0.17 to 0.33 ± 0.07. However, Crs (0.45 ± 0.14 ml ⋅ cmH2O−1 ⋅ kg−1at starting CDP point) remained unchanged through lung volume optimization but appeared inversely related to OCDP. Similarly, respiratory system resistance was not affected. We conclude that there is a marked dissociation between oxygenation improvement and Crs profile during the initial phase of lung recruitment by early high-frequency oscillatory ventilation in infants with RDS. Thus optimal lung volume cannot be defined by serial Crs measurement. At the most, low initial Crs suggests that higher CDP will be needed.

Effect of I/E ratio on mean alveolar pressure during high-frequency oscillatory ventilation

1999 ◽  
Vol 87 (1) ◽  
pp. 407-414 ◽  
Author(s):  
J. J. Pillow ◽  
H. Neil ◽  
M. H. Wilkinson ◽  
C. A. Ramsden
Keyword(s):  
High Frequency ◽  
High Frequency Oscillatory Ventilation ◽  
Lung Model ◽  
Alveolar Pressure ◽  
Expiratory Time ◽  
Oscillatory Ventilation ◽  
Airway Opening ◽  
Mean Pressure ◽  
High Frequency Oscillatory

This study investigated factors contributing to differences between mean alveolar pressure ([Formula: see text]) and mean pressure at the airway opening (Pao) during high-frequency oscillatory ventilation (HFOV). The effect of the inspiratory-to-expiratory time (I/E) ratio and amplitude of oscillation on the magnitude of [Formula: see text] −Pao (Pdiff) was examined by using the alveolar capsule technique in normal rabbit lungs ( n = 4) and an in vitro lung model. The effect of ventilator frequency and endotracheal tube (ETT) diameter onPdiff was further examined in the in vitro lung model at an I/E ratio of 1:2. In both lung models,[Formula: see text] fell belowPao during HFOV when inspiratory time was shorter than expiratory time. Under these conditions, differences between inspiratory and expiratory flows, combined with the nonlinear relationship between resistive pressure drop and flow in the ETT, are the principal determinants of Pdiff. In our experiments, the magnitude of Pdiff at each combination of I/E, frequency, lung compliance, and ETT resistance could be predicted from the difference between the mean squared inspiratory and expiratory velocities in the ETT. These observations provide an explanation for the measured differences in mean pressure between the airway opening and the alveoli during HFOV and will assist in the development of optimal strategies for the clinical application of this technique.

Respiratory mechanics during high-frequency oscillatory ventilation: a physical model and preterm infant study

2012 ◽  
Vol 112 (7) ◽  
pp. 1105-1113 ◽  
Author(s):  
Rachana Singh ◽  
Sherry E. Courtney ◽  
Michael D. Weisner ◽  
Robert H. Habib
Keyword(s):  
Mechanical Properties ◽  
Preterm Infants ◽  
High Frequency ◽  
Respiratory Mechanics ◽  
High Frequency Oscillatory Ventilation ◽  
Test Lung ◽  
Oscillatory Ventilation ◽  
Effective Removal ◽  
Airway Opening ◽  
High Frequency Oscillatory

Accurate mechanics measurements during high-frequency oscillatory ventilation (HFOV) facilitate optimizing ventilator support settings. Yet, these are influenced substantially by endotracheal tube (ETT) contributions, which may dominate when leaks around uncuffed ETT are present. We hypothesized that 1) the effective removal of ETT leaks may be confirmed via direct comparison of measured vs. model-predicted mean intratracheal pressure [mPtr (meas) vs. mPtr (pred)], and 2) reproducible respiratory system resistance (Rrs) and compliance (Crs) may be derived from no-leak oscillatory Ptr and proximal flow. With the use of ETT test-lung models, proximal airway opening (Pao) and distal (Ptr) pressures and flows were measured during slow-cuff inflations until leaks are removed. These were repeated for combinations of HFOV settings [frequency, mean airway pressure (Paw), oscillation amplitudes (ΔP), and inspiratory time (%tI)] and varying test-lung Crs. Results showed that leaks around the ETT will 1) systematically reduce the effective distending pressures and lung-delivered oscillatory volumes, and 2) derived mechanical properties are increasingly nonphysiologic as leaks worsen. Mean pressures were systematically reduced along the ventilator circuit and ETT (Paw > Pao > Ptr), even for no-leak conditions. ETT size-specific regression models were then derived for predicting mPtr based on mean Pao (mPao), ΔP, %tI, and frequency. Next, in 10 of 11 studied preterm infants (0.77 ± 0.24 kg), no-to-minimal leak was confirmed based on excellent agreement between mPtr (meas) and mPtr (pred), and consequently, their oscillatory respiratory mechanics were evaluated. Infant resistance at the proximal ETT (RETT; resistance airway opening = RETT + Rrs; P < 0.001) and ETT inertance ( P = 0.014) increased significantly with increasing ΔP (50%, 100%, and 150% baseline), whereas Rrs showed a modest, nonsignificant increase ( P = 0.14), and Crs was essentially unchanged ( P = 0.39). We conclude that verifying no-leak conditions is feasible by comparison of model-derived vs. distending mPtr (meas). This facilitated the reliable and accurate assessment of physiologic respiratory mechanical properties that can objectively guide ventilatory management of HFOV-treated preterm infants.

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