Transmission of Oscillatory Volumes into the Preterm Lung during Noninvasive High-Frequency Ventilation.

RATIONALE There is increasing evidence for a clinical benefit of noninvasive high-frequency oscillatory ventilation (nHFOV) in preterm infants. However, it is still unknown whether the generated oscillations are effectively transmitted to the alveoli. OBJECTIVES To assess magnitude and regional distribution of oscillatory volumes (VOsc) at the lung level. METHODS In 30 prone preterm infants enrolled in a randomized crossover trial comparing nHFOV with nasal continuous positive airway pressure (nCPAP), electrical impedance tomography (EIT) recordings were performed. During nHFOV, the smallest amplitude to achieve visible chest wall vibration was used, and the frequency was set at 8 hertz (Hz). MEASUREMENTS AND MAIN RESULTS Thirty consecutive breaths during artefact-free tidal ventilation were extracted for each of the 228 EIT recordings. After application of corresponding frequency filters, tidal volumes (VT) and VOsc were calculated. There was a signal at 8 and 16 Hz during nHFOV which was not detectable during nCPAP, corresponding to the set oscillatory frequency and its second harmonic. During nHFOV, the mean (SD) VOsc/VT ratio was 0.20 (0.13). Oscillations were more likely to be transmitted to the non-gravity-dependent [mean difference (95% CI): 0.041 (0.025 to 0.058); p<0.001] and right-sided lung [mean difference (95% CI): 0.040 (0.019 to 0.061); p<0.001] when compared with spontaneous VT. CONCLUSIONS In preterm infants, VOsc during nHFOV are transmitted to the lung. Compared with the regional distribution of tidal breaths, oscillations preferentially reach the right and non-gravity-dependent lung. These data increase our understanding of the physiological processes underpinning nHFOV and may lead to further refinement of this novel technique.