Detection of expiratory flow limitation in COPD using the forced oscillation technique

• Published in: The European respiratory journal Vol. 23; no. 2; pp. 232 - 240
• Main Authors: Dellaca, R.L, Santus, P, Aliverti, A, Stevenson, N, Centanni, S, Macklem, P.T, Pedotti, A, Calverley, P.M.A
• Format: Journal Article
• Language: English
• Published: Leeds Eur Respiratory Soc 01-02-2004; Maney
• Subjects: Aged; Air Pressure; Airway Resistance - physiology; Biological and medical sciences; Chronic obstructive pulmonary disease, asthma; Exhalation - physiology; Female; Forced Expiratory Flow Rates - physiology; Humans; Lung Volume Measurements; Male; Medical sciences; Middle Aged; Oscillometry - methods; Pneumology; Pulmonary Alveoli - physiopathology; Pulmonary Disease, Chronic Obstructive - diagnosis; Pulmonary Disease, Chronic Obstructive - physiopathology; Reference Values; Respiratory Mechanics - physiology; Lung disease; Respiratory disease; within-breath reactance; forced oscillation technique; Respiratory system; respiratory reactance; Respiratory tract; Chronic; Forced oscillation; Limitation; Bronchus disease; Chronic obstructive pulmonary disease; Obstructive pulmonary disease; Technique; Detection; Impedance; Pneumology
• ISSN: 0903-1936; 1399-3003
• DOI: 10.1183/09031936.04.00046804

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 (deltaXrs) and minimum expiratory Xrs (Xexp,min) identified flow-limited breaths with 100% specificity and sensitivity using a threshold between 2.53-3.12 cmH2O x s x L(-1) (deltaXrs) and -7.38- -6.76 cmH2O x s x 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. Within-breath respiratory system reactance provides an accurate, reliable and noninvasive technique to detect expiratory flow limitation in patients with chronic obstructive pulmonary disease.