Published ahead of print on April 26, 2007, doi:10.1164/rccm.200609-1317OC Am. J. Respir. Crit. Care Med., Volume 176, Number 2, July 2007, 129-137 A more recent version of this article appeared on July 15, 2007
Submitted on September 14, 2006 Airway Distensibility in Asthmatic and Healthy Adults Measured by Forced Oscillation TechniqueNathan J Brown1*,1 The Woolcock Institute of Medical Research, Camperdown, NSW, Australia; Department of Medicine, The University of Sydney, Sydney, NSW, Australia; The Cooperative Research Centre for Asthma, Sydney, Australia, 2 The Cooperative Research Centre for Asthma, Sydney, Australia; Bioengineering Institute, The University of Auckland, Auckland, New Zealand * To whom correspondence should be addressed. E-mail: njb{at}woolcock.org.au.
Rationale: Reduced airway distensibility in asthmatics compared with controls may be related to differences in lung elastic recoil and bronchomotor tone. Objectives: To examine the contribution of lung elastic recoil and bronchomotor tone to airway distensibility. Methods: We compared airway distensibility in 18 asthmatics with 19 controls before and after bronchodilator and, in a subgroup of 7 asthmatics and 8 controls, correlated distensibility with pressure-volume parameters. Measurements: Distensibility was measured, using forced oscillation technique, as the linear slope of conductance vs volume between TLC and 75%TLC and between 75%TLC and FRC. Transpulmonary pressure was recorded concurrently with distensibility, using an esophageal balloon. Pressure-conductance data were described using linear regressions and pressure-volume data were described using exponential equations. Main Results: Asthmatics had lower baseline FEV1 (p=0.0003) and conductance (p=0.002) than controls. Distensibility above 75%TLC was less in asthmatics than controls (p<0.0001) but there was no difference below 75%TLC. Bronchodilator did not alter distensibility despite increases in FEV1 (p=0.0002) and conductance (p<0.0001) in asthmatics, and conductance (p=0.0004) in controls. After bronchodilator, asthmatics had reduced lung elastic recoil compared with controls (p=0.03) and a reduced pressure- conductance slope (p=0.01) but there were no correlations between pressure-volume characteristics and airway distensibility. Conclusions: Airway distensibility measured by FOT is reduced in asthmatics compared with non-asthmatics, is not related to lung elastic recoil and is unchanged by bronchodilator. Airway wall remodeling remains the most likely cause of reduced airway distensibility in asthma. Key words: Respiratory mechanics, oscillometry, bronchi
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