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Contribution of nasal pathways to low frequency respiratory impedance in infants
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  1. G L Hall1,2,
  2. Z Hantos1,2,3,
  3. J H Wildhaber4,
  4. P D Sly1,2
  1. 1Division for Clinical Sciences, Institute for Child Health Research, University of Western Australia
  2. 2Centre for Child Health Research, University of Western Australia
  3. 3Department of Medical Informatics and Engineering, University of Szeged, Hungary
  4. 4Respiratory Medicine, University Children's Hospital, Zurich, Switzerland
  1. Correspondence to:
    Dr G L Hall, Respiratory Medicine, Princess Margaret Hospital for Children, GPO Box D184, Perth, 6840, Australia;
    graham{at}ichr.uwa.edu.au

Abstract

Background: In infants the impedance of the nasal pathways (Zn) is a significant proportion of the total respiratory impedance (Zrs).

Methods: In 11 infants Zrs was partitioned into Zn and lower respiratory system impedance (Zlrs) using a nasal catheter. A low frequency oscillatory signal (0.5–20 Hz) was applied during a pause in breathing to obtain the impedance spectra. A model of the respiratory system containing an airway and tissue compartment was then fitted to Zrs and Zlrs. The airway compartment consisted of a frequency independent resistance (R) and inertance (I), while the tissue compartment was described by coefficients of tissue damping (G) and elastance (H).

Results: Zrs could be reliably partitioned into Zn and Zlrs. The nasal pathway acted as a purely resistive-inertive impedance and contributed approximately half of the airway resistance (mean (SE) 44.6 (4.9)%) and most of the respiratory system inertance (71.7 (3.5)%).

Conclusion: In studies investigating changes in airway resistance in nasally breathing infants, the separation of nasal and lower respiratory system mechanics will increase the sensitivity of the tests.

  • nasal resistance
  • respiratory impedance
  • infant lung function
  • G, tissue damping
  • H, tissue elastance
  • I, inertance
  • Rn, nasal resistance
  • Rrs, resistance of the respiratory system
  • TGV, thoracic gas volume
  • Xn, nasal reactance
  • Xrs, reactance of the respiratory system
  • Zn, impedance of the nasal pathways
  • Zrs, total respiratory impedance
  • Zlrs, impedance of the lower respiratory system

https://doi.org/10.1136/thorax.57.5.396

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