Non-invasive detection of expiratory flow limitation in COPD patients during nasal CPAP

¹ TBM Lab, Dipartimento di Bioingegneria, Politecnico di Milano University, Milano, Italy
² Unitat de Biofísica i Bioenginyeria, Facultat de Medicina, Universidad de Barcelona-IDIBAPS, Barcelona, Spain

	Abstract

The difference between inspiratory and expiratory respiratory reactance (Xrs) measured by forced oscillation technique (FOT) at 5 Hz allows the detection of expiratory flow limitation (EFL) in COPD patients breathing spontaneously. This study was aimed to evaluate whether this approach can be applied to COPD patients during non-invasive pressure support.

Xrs was measured in 7 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 esophageal pressure and the Mead and Whittenberger (M-W) method provided a reference to score each breath as flow-limited (FL), non-flow-limited (NFL) or indeterminate (I). For each patient, we analysed 6 consecutive breaths for each posture and CPAP level.

According to M-W scoring, 47 breaths were FL, 166 NFL and 51 I. EFL scoring by FOT coincided with M-W in 94.8% of the breaths. In the 4 patients that were FL in at least one condition, Xrs was reduced with increasing CPAP.

These data suggest that FOT may be useful in COPD patients on nasal pressure support by identifying CPAP 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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