Respiratory inductance plethysmography calibration for pediatric upper airway obstruction: an animal model

BACKGROUND: We sought to determine optimal methods of respiratory inductance plethysmography (RIP) flow calibration for application to pediatric postextubation upper airway obstruction. METHODS: We measured RIP, spirometry, and esophageal manometry in spontaneously breathing, intubated Rhesus monkeys with increasing inspiratory resistance. RIP calibration was based on: Delta mu V-ao approximate to M[Delta mu V-RC + K(Delta mu V-AB)] where K establishes the relationship between the uncalibrated rib cage (Delta mu V-RC) and abdominal (Delta mu V-AB) RIP signals. We calculated K during (i) iso-volume maneuvers during a negative inspiratory force (NIF), (ii) quantitative diagnostic calibration (QDC) during (a) tidal breathing, (b) continuous positive airway pressure (CPAP), and (c) increasing degrees of upper airway obstruction (UAO). We compared the calibrated RIP flow waveform to spirometry quantitatively and qualitatively. RESULTS: Isovolume calibrated RIP flow tracings were more accurate (against spirometry) both quantitatively and qualitatively than those from QDC (P < 0.0001), with bigger differences as UAO worsened. Isovolume calibration yielded nearly identical clinical interpretation of inspiratory flow limitation as spirometry. CONCLUSION: In an animal model of pediatric UAO, isovolume calibrated RIP flow tracings are accurate against spirometry. QDC during tidal breathing yields poor RIP flow calibration, particularly as UAO worsens. Routine use of a NIF maneuver before extubation affords the opportunity to use RIP to study postextubation UAO in children.