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Copyright ©ERS Journals Ltd 2004
Detection of expiratory flow limitation in COPD using the forced oscillation technique
1 TBMLab, Dipartimento di Bioingegneria, Politecnico di Milano University and 2 Respiratory Unit, Institute of Lung Disease, San Paolo Hospital, University of Milan, Milan, Italy. 3 University Hospital Aintree, University Dept of Medicine, Liverpool, UK. 4 Respiratory Division, Meakins-Christie Laboratories, MUHC Research Institute, McGill University, Montreal, Canada
CORRESPONDENCE: R.L. Dellacà, Dipartimento di Bioingegneria, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133, Milan, Italy. Fax: 39 0223999000. E-mail: dellaca@biomed.polimi.it
Keywords: chronic obstructive pulmonary disease, forced oscillation technique, impedance, respiratory reactance, within-breath reactance
Received: April 28, 2003
Accepted October 7, 2003
This work was supported by the European Community CARED FP5 Project (Contract number QLRT-2001-0893).
Expiratory flow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperinflation and exercise limitation in chronic obstructive pulmonary disease (COPD). Current methods of detecting this are either invasive or unsuited to following changes breath-by-breath. It was hypothesised that tidal flow limitation would substantially reduce the total respiratory system reactance (Xrs) during expiration, and that this reduction could be used to reliably detect if EFL was present.
To test this, 5-Hz forced oscillations were applied at the mouth in seven healthy subjects and 15 COPD patients (mean±sd forced expiratory volume in one second was 36.8±11.5 % predicted) during quiet breathing. COPD breaths were analysed (n=206) and classified as flow-limited if flow decreased as alveolar pressure increased, indeterminate if flow decreased at constant alveolar pressure, or nonflow-limited.
Of these, 85 breaths were flow-limited, 80 were not and 41 were indeterminate. Among other indices, mean inspiratory minus mean expiratory Xrs (
Within-breath respiratory system reactance provides an accurate, reliable and noninvasive technique to detect expiratory flow limitation in patients with chronic obstructive pulmonary disease.
Xrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2.53–3.12 cmH2O·s·L–1 (Xrs) and –7.38– –6.76 cmH2O·s·L–1 (Xexp,min) representing 6.0% and 3.9% of the total range of values respectively. No flow-limited breaths were seen in the normal subjects by either method.
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