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Published online before print November 1, 2006
Eur Respir J 2006, doi:10.1183/09031936.00038006
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ORIGINAL ARTICLE

Expiratory flow-limitation detected by forced oscillation and negative expiratory pressure

R.L. Dellacà 1*, N. Duffy 2, P.P. Pompilio 1, A. Aliverti 1, N.G. Koulouris 3, A. Pedotti 1, P.M.A. Calverley 2

1 TBM Lab, Dipartimento di Bioingegneria, Politecnico di Milano University, Milano, Italy
2 University Hospital Aintree, University Department of Medicine, Liverpool, UK
3 Respiratory Function Laboratory, Dept. of Respiratory Medicine, University of Athens Medical School, "Sotiria" Hospital, Athens, Greece.

* To whom correspondence should be addressed. E-mail: raffaele.dellaca{at}polimi.it.


  Abstract

The within-breath change in reactance (DXrs) measured by forced oscillation technique (FOT) at 5Hz reliably detects expiratory flow-limitation (EFL) in COPD. In this study we compared this approach to the standard negative expiratory pressure (NEP) method.

We studied 21 COPD patients applying both techniques to the same breath and in 15 repeated the measurements after bronchodilator. For each patient and condition 5 NEP tests were performed and scored independently by three operators unaware of the FOT results.

On 180 tests, FOT classified 53.3% as flow-limited (FL). On average, the operators scored 27.6% of tests FL, 47.6% non-FL but could not score 24.8%. The methods disagreed in 7.9% and in 78% of these the NEP scores differed between operators. Bronchodilation reduced NEP and DXrs scores, only the latter achieving significance (p=0.02). Averaging the operators' NEP scores, a threshold between 24.6%-30.8% of tidal volume being FL by NEP produced 94% agreement between methods.

In conclusion, when NEP and FOT were both available they showed good agreement. As FOT is automatic and can measure multiple breaths over long periods, it is suitable for monitoring EFL continuously and identifying patients breathing close to the onset of EFL, where intermittent sampling may by unrepresentative.

Keywords:  Chronic obstructive pulmonary disease, forced oscillation technique, respiratory system reactance, within-breath impedance




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