Contribution of nasal pathways to low frequency respiratory impedance in infants
- 1Division for Clinical Sciences, Institute for Child Health Research, University of Western Australia
- 2Centre for Child Health Research, University of Western Australia
- 3Department of Medical Informatics and Engineering, University of Szeged, Hungary
- 4Respiratory Medicine, University Children's Hospital, Zurich, Switzerland
- Correspondence to:
Dr G L Hall, Respiratory Medicine, Princess Margaret Hospital for Children, GPO Box D184, Perth, 6840, Australia;
- Accepted 20 November 2001
- Revised 16 November 2001
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.
- 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