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J Appl Physiol (May 3, 2007). doi:10.1152/japplphysiol.00420.2006
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Submitted on April 10, 2006
Accepted on April 17, 2007

Short term variability of airway calibre - a marker of asthma?

Chantale Diba1*, Cheryl M Salome2, Helen K Reddel1, C. William Thorpe3, Brett Toelle4, and Gregory G. King5

1 The Woolcock Institute of Medical Research, New South Wales, Australia; The University of Sydney, Sydney, New South Wales, Australia
2 Woolcock Institute of Medical Research, PO Box M77,, Sydney, New South Wales, 2050, Australia; The University of Sydney, Sydney, New South Wales, Australia
3 The Bioengineering Institute, Auckland, New Zealand; The Woolcock Institute of Medical Research, New South Wales, Australia; Cooperative Research Centre for Asthma, Sydney, New South Wales, Australia
4 Woolcock Institute of Medical Research, Sydney, New South Wales, Australia; The University of Sydney, Sydney, New South Wales, Australia
5 Woolcock Institute, University of Sydney, PO Box M77, Sydney, New South Wales, 2050, Australia; Respiratory Department, Royal North Shore Hospital, Sydney, New South Wales, Australia; The University of Sydney, Sydney, New South Wales, Australia; Cooperative Research Centre for Asthma, Sydney, New South Wales, Australia

* To whom correspondence should be addressed. E-mail: chantale{at}woolcock.org.au.

Variability in airway calibre is a characteristic feature of asthma. Previous studies reported that the variability in respiratory system impedance (Zrs), measured by the forced oscillation technique during several minutes of tidal breathing, is increased in asthma and may be a marker of inherent instability of the airways. The aims of this study were to determine if short-term variability in impedance correlates with peak flow (PEF) variability or airway hyperresponsiveness (AHR). The standard deviation of log transformed impedance (lnZrsSD) was measured as a marker of short-term variability, and compared to the diurnal variability of PEF over two weeks in 28 asthmatic and seven non-asthmatic subjects and to AHR to histamine in a cohort of 17 asthmatic and 82 non-asthmatic subjects. In addition, lnZrsSD was measured in eight non-asthmatic subjects before and after methacholine challenge in the upright and supine positions. There were no significant differences in lnZrsSD between asthmatic and non-asthmatic subjects (p=0.68). Furthermore, in asthmatic subjects lnZrsSD did not correlate with diurnal variability of PEF (rs =-0.12 p=0.54), or with AHR to histamine (r=0.10, p=0.71). Neither methacholine challenge nor supine posture caused any significant change in lnZrsSD. We conclude that our findings do not support previous reports about the utility of short-term variability of impedance. Our findings suggest that, using standard methods for forced oscillometry, impedance variability does not provide clinically useful information about the severity of asthma.




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