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Expiratory flow limitation during mechanical ventilation detected by the forced oscillation method
M Vassiliou1, R Peslin, C Saunier
1Unité 14 de Physiopathologie Respiratoire, Institut National de la Santé et de la Recherche Médicale, Université H. Poincaré Nancy 1, Vandoeuvre-les-Nancy, France.
The European Respiratory Journal
|April 1, 1996
Summary
Detecting expiratory flow limitation (EFL) in mechanically ventilated patients with chronic obstructive pulmonary disease (COPD) is crucial. This study found that a significant drop in the imaginary part of respiratory impedance during exhalation reliably indicates EFL.
Area of Science:
- Respiratory Physiology
- Medical Engineering
- Pulmonology
Background:
- Phasic variations in respiratory mechanical impedance were previously noted in mechanically ventilated COPD patients.
- These variations were hypothesized to be caused by expiratory flow limitation (EFL).
Purpose of the Study:
- To experimentally validate the link between respiratory impedance variations and EFL.
- To assess the utility of impedance measurements for noninvasive, automatic detection of EFL during mechanical ventilation.
Main Methods:
- Experiments were conducted using a mechanical analogue with a flow-limiting element and in anesthetized rabbits.
- Expiratory flow limitation (EFL) was induced by adjusting expiratory pressure.
- Respiratory impedance was measured using 15 Hz oscillations, analyzing real (Re) and imaginary (Im) components during inspiration and expiration.
Main Results:
- In the mechanical analogue, EFL caused significant decreases in both Re and Im during expiration.
- In rabbits, EFL specifically and systematically reduced the imaginary part (Im) of impedance during expiration.
- A -50% threshold for Im decrease demonstrated 96% sensitivity and 100% specificity for detecting EFL.
Conclusions:
- A substantial decrease in the imaginary part of respiratory impedance during expiration is a sensitive and specific indicator of expiratory flow limitation.
- This finding supports the use of impedance monitoring for noninvasive detection of EFL in artificially ventilated patients.