Effect of amplitude and inspiratory time in a bench model of non-invasive HFOV through nasal prongs

Background and objectives Non-invasive high frequency oscillatory ventilation through nasal prongs (nHFOV) has been proposed to combine the advantages of oscillatory pressure waveform and non-invasive interface. We studied the effect of oscillation amplitude and inspiratory time on the pressure transmission and tidal volume delivery through different nasal prongs. Methods In vitro mechanical study on a previously described bench model of nHFOV. The model was built connecting SM3100A tubings to a neonatal lung model, via two differently sized binasal prongs. A circuit with no nasal prongs was used as control. Tidal volume (Tv), oscillatory pressure ratio (?Pdist/?Pprox), and ventilation (DCO2) were measured across a range of amplitudes and inspiratory times (IT). Measurements were performed with a low-dead space hot wire anemometer coupled with a pressure transducer. Results Using both nasal prongs, Tv, ?Pdist/?Pprox, and DCO2 were 83%, 40%, and 71%, respectively, of those provided with the control circuit. No differences were noticed between small and large prongs. Tv and ?Pprox were linked by a quadratic relationship. Tv plateaus for amplitude values >65?cmH2O. ?Pdist/?Pprox shows same tendency. Same results were obtained with both types of prongs and with increasing IT. On the whole, mean Tv was higher with IT at 50% than at 33% (2.4?ml vs. 1.4?ml; P?<?0.001). Conclusions Changing oscillation amplitude and IT has a significant effect on ventilation. Varying these two parameters provides a theoretical Tv within the ideal values for HFOV also using the smallest nasal prongs. Pediatr Pulmonol. 2012. 47:10121018. (c) 2012 Wiley Periodicals, Inc.