Respiratory mechanics studied by forced oscillations during artificial ventilation

Area of Science:

• Respiratory Physiology
• Critical Care Medicine
• Biomedical Engineering

Background:

• Forced oscillation technique (FOT) offers advantages for monitoring respiratory mechanics during mechanical ventilation, including no need for patient relaxation.
• FOT can provide additional data from the frequency dependence of respiratory impedance (real and imaginary parts).

Purpose of the Study:

• To assess the feasibility and usefulness of FOT in intubated patients undergoing mechanical ventilation for acute respiratory failure.
• To investigate the application of FOT for analyzing respiratory mechanics throughout the respiratory cycle.

Main Methods:

• Applied sinusoidal pressure oscillations (5, 10, 20 Hz) at the airway opening in 17 intubated, mechanically ventilated patients.
• Corrected impedance data for endotracheal tube impedance and computed real and imaginary parts separately for inspiration and expiration.
• Utilized a model with central airways and a peripheral pathway in parallel with bronchial compliance for data analysis.

Main Results:

• Real part of impedance often decreased with increasing frequency and was larger during inspiration.
• Imaginary part of impedance typically increased with frequency during expiration but showed variable behavior during inspiration.
• Standard resistance-inertance-compliance models were insufficient; a more complex model better explained the data, suggesting dynamic airway compression.

Conclusions:

• FOT is relatively easy to implement during mechanical ventilation.
• FOT allows detailed study of respiratory mechanics at different respiratory cycle points.
• FOT may aid in detecting expiratory flow limitation in mechanically ventilated patients.