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Airway and tissue mechanics in anesthetized paralyzed children
Ferenc Peták1, Barna Babik, Tibor Asztalos
1Department of Medical Informatics and Engineering, University of Szeged, Szeged, Hungary. petak@dmi.u-szeged.hu
Insights
Anesthesia and paralysis enable accurate measurement of respiratory system impedance (Zrs) in children. This method effectively separates lung and chest wall mechanics, allowing for precise estimation of airway and tissue properties.
Area of Science:
- Pediatric critical care medicine
- Respiratory physiology
- Biomedical engineering
Background:
- Estimating respiratory and tissue mechanics in children is crucial for managing mechanical ventilation.
- Low-frequency forced oscillations offer a non-invasive method to assess respiratory system impedance (Zrs).
Purpose of the Study:
- To determine the mechanical properties of airways and respiratory tissues in anesthetized, paralyzed children.
- To partition Zrs into pulmonary (Z(L)) and chest wall (Z(W)) components.
- To validate the use of Zrs for estimating airway properties in mechanically ventilated children.
Main Methods:
- Respiratory system impedance (Zrs) was measured using low-frequency forced oscillations (0.4-12 Hz) in 26 children.
- Tracheal flow and pressure signals were used to calculate Zrs.
- Esophageal pressure was measured in 5 children to determine Z(L) and Z(W).
- A model of respiratory mechanics (R, I, G, H) was fitted to the impedance spectra.
Main Results:
- Normalized respiratory parameters (R, I, G, H) were quantified.
- The lungs significantly contributed to resistance (R) and inertance (I).
- Lung parenchyma was the primary contributor to tissue damping (G) and elastance (H).
Conclusions:
- Anesthesia and paralysis create optimal conditions for measuring Zrs and its components in ventilated children.
- Zrs measurements can reliably estimate airway properties.
- Chest wall mechanics may influence the observed parenchymal properties.
Abstract:
To estimate the mechanical properties of the airways and respiratory tissues, respiratory system impedance (Zrs) was measured with low-frequency forced oscillations in 26 anesthetized, paralyzed children (aged 3 months-10 years) undergoing surgical correction of congenital heart diseases. Zrs was determined from the signals of tracheal flow and pressure between 0.4-12 Hz before surgery at zero mean transrespiratory pressure. The pulmonary (Z(L)) and chest wall (Z(W)) components of Zrs were also determined in 5 children by measuring esophageal pressure. A model containing frequency-independent resistance (R) and inertance (I), and coefficients of tissue-damping (G) and elastance (H), was fitted to the Zrs, Z(L), and Z(W) spectra. The total respiratory parameters normalized to body weights were 82.2 +/- 8.5 (SE) hPa x sec x l(-1) x kg, 0.152 +/- 0.05 hPa x sec(2) x l(-1) x kg, 293.8 +/- 20.0 hPa. l(-1) x kg, and 1,583 +/- 65.5 hPa x l(-1) x kg, for R, I, G, and H, respectively. The measurements of Z(L) and Z(W) revealed the dominance of the lungs in R (91 +/- 4.3%) and I (109 +/- 16%), and the major contribution of the lung parenchyma to G (61 +/- 7.3%) and H (66 +/- 7.4%) of the total respiratory system. It is concluded that anesthesia-paralysis provides an ideal condition for the measurement of low-frequency forced oscillatory impedance and its partitioning into airway and tissue components in mechanically ventilated children. The separation of pulmonary and chest wall mechanics demonstrates that airway properties can be estimated appropriately from Zrs data, while the chest wall may damp the changes in parenchymal properties.