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A single-compartment model cannot describe passive expiration in intubated, paralysed humans
G L Chelucci1, F Brunet, J Dall'Ava-Santucci
1Dipartimento di Fisiopatologia Clinica, Università di Firenze, Italy.
The European Respiratory Journal
|April 1, 1991
Summary
Mechanically ventilated patients exhibit two distinct expiratory mechanisms. A rapid phase empties most volume, while a slower phase reflects lung and chest wall viscoelastic properties.
Area of Science:
- Respiratory Physiology
- Biomechanics
Background:
- Understanding the mechanics of relaxed expiration is crucial for mechanical ventilation management.
- Previous studies have not fully elucidated the distinct phases and underlying mechanisms of exhalation during controlled ventilation.
Purpose of the Study:
- To investigate the time-course of thoracic volume changes during relaxed expiration in intubated, paralyzed, mechanically ventilated subjects.
- To identify and characterize the different mechanisms governing exhalation in this population.
Main Methods:
- Utilized respiratory inductive plethysmography to measure thoracic volume changes.
- Analyzed semilog volume-time curves during relaxed expiration in 11 mechanically ventilated subjects.
- Evaluated expiratory time constants for different tidal volumes.
Main Results:
- Identified two distinct phases in the expiratory volume-time curves.
- A rapid phase (time constant ~0.5 s) accounted for ~80% of expired volume, likely reflecting elastic and resistive properties.
- A slower phase (time constant ~3.3 s) contributed a smaller volume, suggesting viscoelastic properties of pulmonary and chest wall tissues.
Conclusions:
- Mechanically ventilated exhalation involves at least two distinct processes.
- The rapid phase is attributed to standard respiratory system properties.
- The slower phase likely represents the viscoelastic behavior of lung and chest wall tissues.