ORIGINAL ARTICLE

Contribution of nasal pathways to low frequency respiratory impedance in infants

G L Hall^1,2, Z Hantos^1,2,3, J H Wildhaber⁴, P D Sly^1,2

¹ Division for Clinical Sciences, Institute for Child Health Research, University of Western Australia
² Centre for Child Health Research, University of Western Australia
³ Department of Medical Informatics and Engineering, University of Szeged, Hungary
⁴ Respiratory Medicine, University Children's Hospital, Zurich, Switzerland

Correspondence to:
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

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.

Keywords: nasal resistance; respiratory impedance; infant lung function

Abbreviations: 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

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