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Noninvasive detection of expiratory flow limitation in COPD patients during nasal CPAP

¹ TBM Lab, Dipartimento di Bioingegneria, Politecnico di Milano University, Milan, Italy. ² Unitat de Biofísica i Bioenginyeria, Facultat de Medicina, Universidad de Barcelona-l'Institut d'Investigacions Biomèdiques August Pi i Sunyer, Barcelona, Spain.

CORRESPONDENCE: R. L. Dellacà, Dipartimento di Bioingegneria, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy. Fax: 39 0223999000. E-mail: raffaele.dellaca{at}polimi.it

Keywords: Forced oscillation technique, noninvasive mechanical ventilation, respiratory system reactance, within-breath impedance

Received: July 8, 2005
Accepted December 24, 2005

The difference between mean inspiratory and expiratory respiratory reactance (_rs) measured with forced oscillation technique (FOT) at 5 Hz allows the detection of expiratory flow limitation (EFL) in chronic obstructive pulmonary disease (COPD) patients breathing spontaneously. This aim of this study was to evaluate whether this approach can be applied to COPD patients during noninvasive pressure support.

_rs was measured in seven COPD patients subjected to nasal continuous positive airway pressure (CPAP) at 0, 4, 8 and 12 cmH₂O in sitting and supine positions. Simultaneous recording of oesophageal pressure and the Mead and Whittenberger (M–W) method provided a reference for scoring each breath as flow-limited (FL), non-flow-limited (NFL) or indeterminate (I). For each patient, six consecutive breaths were analysed for each posture and CPAP level.

According to M–W scoring, 47 breaths were FL, 166 NFL and 51 I. EFL scoring using FOT coincided with M–W in 94.8% of the breaths. In the four patients who were FL in at least one condition, _rs was reduced with increasing CPAP.

These data suggest that the forced oscillation technique may be useful in chronic obstructive pulmonary disease patients on nasal pressure support by identifying continuous positive airway pressure levels that support breathing without increasing lung volume, which in turn increase the work of breathing and reduce muscle effectiveness and efficiency.

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