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 (T(v) ), oscillatory pressure ratio (ΔP(dist) /ΔP(prox) ), and ventilation (DCO(2) ) were measured across a range of amplitudes and inspiratory times (I(T) ). Measurements were performed with a low-dead space hot wire anemometer coupled with a pressure transducer.

RESULTS: Using both nasal prongs, T(v) , ΔP(dist) /ΔP(prox) , and DCO(2) were 83%, 40%, and 71%, respectively, of those provided with the control circuit. No differences were noticed between small and large prongs. T(v) and ΔP(prox) were linked by a quadratic relationship. T(v) plateaus for amplitude values >65 cmH(2) O. ΔP(dist) /ΔP(prox) shows same tendency. Same results were obtained with both types of prongs and with increasing I(T) . On the whole, mean T(v) was higher with I(T) at 50% than at 33% (2.4 ml vs. 1.4 ml; P < 0.001).

CONCLUSIONS: Changing oscillation amplitude and I(T) has a significant effect on ventilation. Varying these two parameters provides a theoretical T(v) within the ideal values for HFOV also using the smallest nasal prongs.