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

ABSTRACT: Expiratory ¯ ow limitation (EFL) during tidal breathing is a major determinant of dynamic hyperin¯ ation 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 ¯ ow 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 classi® ed as ¯ ow-limited if ¯ ow decreased as alveolar pressure increased, indeterminate if ¯ ow decreased at constant alveolar pressure, or non¯ ow-limited Of these, 85 breaths were ¯ ow-limited, 80 were not and 41 were indeterminate Among other indices, mean inspiratory minus mean expiratoryXrs (D Xrs) and minimum expiratoryXrs (Xexp,min) identi® ed ¯ ow-limited breathswith 100% speci® city and sensitivity using a threshold between 2 53±3 12 cmH2O· s·L-1 (D 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 ¯ ow-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 ¯ ow limitation in patients with chronic obstructive pulmonary disease Eur Respir J 2004; 23: 232± 240