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Frequency dependence of elastance and resistance in ventilated children with and without the chest opened
T Nicolai1, C J Lanteri, P D Sly
1Division of Clinical Sciences, Western Australian Research Institute for Child Health, Perth.
Insights
Respiratory mechanics in mechanically-ventilated children show frequency-dependent behavior. Elastance increases and resistance decreases with breathing frequency, a pattern unaffected by chest wall status.
Area of Science:
- Pediatric Critical Care Medicine
- Respiratory Physiology
- Anesthesiology
Background:
- Understanding respiratory mechanics is crucial for managing respiratory failure in mechanically-ventilated children.
- Simple, noninvasive measurement techniques are needed to model the respiratory system.
Purpose of the Study:
- To investigate the frequency dependence of respiratory system and lung elastance and resistance in anesthetized, paralyzed, and mechanically-ventilated children.
- To determine if the chest wall contributes significantly to this frequency-dependent behavior.
Main Methods:
- Eight children (2-56 months) undergoing open-heart surgery were studied.
- Respiratory mechanics (elastance and resistance) were measured using multilinear regression with the chest wall intact and opened.
- Measurements were repeated after brief changes in ventilation frequency.
Main Results:
- Both the total respiratory system and the lungs exhibited frequency-dependent behavior.
- Elastance increased with frequency, while resistance decreased with frequency.
- This pattern remained consistent regardless of whether the chest wall was intact or opened.
Conclusions:
- The observed frequency-dependent behavior in respiratory mechanics is inherent to the respiratory system and lungs, not solely the chest wall.
- These findings are consistent with a linear viscoelastic model (Kelvin body).
- Frequency-dependent behavior must be considered when using respiratory mechanics to monitor disease progression in mechanically-ventilated children.
Abstract:
Measurements of respiratory mechanics in mechanically-ventilated children are potentially useful for understanding the pathogenesis and progress of diseases resulting in respiratory failure. Measurement techniques that can be simply and noninvasively employed model the respiratory system as a single compartment. The frequency dependence of elastance and resistance, both of the total respiratory system and of the lungs, was investigated in eight children (aged 2-56 months) undergoing open-heart surgery. The children were studied whilst anaesthetized, paralysed and mechanically-ventilated. Dynamic elastance (Ers) and resistance (Rrs) of the respiratory system and of the lung (EL, RL) were calculated using a multilinear regression technique, with the chest wall intact, prior to the commencement of surgery, and with the chest wall opened via a mid-line sternotomy. Measurements were repeated after brief (60 s) changes in ventilation frequency. The total respiratory system and the lungs demonstrated frequency-dependent behaviour, with elastance increasing and resistance decreasing with frequency. The pattern of the frequency-dependent behaviour was essentially the same, whether the chest wall was intact or opened, suggesting that the chest wall was not solely responsible for this behaviour in these children. These data are consistent with a linear viscoelastic model containing a Kelvin body. When using measurements of respiratory mechanics to follow the progress of respiratory disease in mechanically-ventilated children, this frequency-dependent behaviour must be taken into account.