[Truncated abstract] Respiratory system impedance (Zrs) is commonly measured at low to medium frequencies (0.5 - 40 Hz) to infer structural and physiological information about the respiratory system. Coupled with the use of mathematical models of the lungs, Zrs has been used to partition the behaviour of the conductive airways and the respiratory tissues. High-frequency (HF) Zrs beyond 100 Hz has been comparatively less studied and understood. Past work has revealed spectral features at high frequencies termed antiresonances, marked by peaks in the real part of Zrs, often coinciding with zero-crossings in the imaginary part. It has been shown that the first occurrence of antiresonance in humans primarily reflects the contribution of the airways, and is a property of sound wave propagation in the airways. Also, the first antiresonance is altered in diseases such as chronic airflow obstruction, and wheeze in infants. The main aim of this project is to shed further understanding about the first antiresonance, via the behaviour of two parameters characterising this feature of the HF spectrum: the frequency at which the first antiresonance occurs, far,1, and the magnitude of the real part of Zrs at this frequency, Rrs(far,1). In our studies, Zrs is measured as an input impedance using the forced oscillation technique with a loudspeaker-in-box and wavetube setup, and employing pseudorandom frequency signals. We studied the effects of altered lung conditions, first in an animal model, then progressed on to humans. v vi In the rat, we found that both far,1 and Rrs(far,1) tended to decrease together with increasing lung volume. With methacholine(MCh)-induced bronchoconstriction, rats showed increases in far,1 and Rrs(far,1) with increasing MCh dose, but these occurred at higher doses compared to increases in airway resistance. The changes in these HF parameters were independent of the changes in tissue properties. ... It was found that in a group of patients with emphysema, VDRrs(far,1) was significantly more negative, potentially due to alterations to airway dimensions and wall properties. Furthermore, VDRrs(far,1) was correlated with extent of obstruction and hyperinflation, suggesting a relationship with severity of emphysema. These results show that the first antiresonance reflect changes in the airways, and its measurement shows promise as a clinical tool, in its potential as an easy-to-perform assessor of conditions in which the airways are altered. Keywords: antiresonance, respiratory input impedance, high frequencies, emphysema
| Identifer | oai:union.ndltd.org:ADTP/221265 |
| Date | January 2006 |
| Creators | Thamrin, Cindy |
| Publisher | University of Western Australia. School of Paediatrics and Child Health |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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