The effects of lung volume recruitment manoeuvres on pulmonary blood flow (PBF) during high-frequency oscillatory ventilation (HFOV) in preterm neonates are unknown. As increased airway pressure adversely affects PBF, we compared the effects of two HFOV recruitment strategies on PBF and oxygenation index (OI). Preterm lambs (128±1d gestation; term ~150d) were anesthetized and ventilated using HFOV (10Hz, 33%t_I) with a mean airway pressure (P_ao) of 15cmH₂O. Lung volume was recruited by either increasing P_ao to 25cmH₂O for 1 min, repeated 5 times at 5 min intervals (Sigh group; n=5) or stepwise (5cmH₂O) changes in P_ao at 5 min intervals incrementing up to 30cmH₂O then decrementing back to 15 cmH₂O (Ramp group; n=6). Controls (n=5) received constant HFOV at 15cmH₂O. PBF progressively decreased (by 45±4%) and OI increased (by 15±6%, indicating reduced oxygenation) in controls during HFOV which was similar to the changes observed in the Sigh group of lambs. In the Ramp group, PBF fell (by 54±10%) as airway pressure increased (r²=0.99), although the PBF did not increase again as the P_ao was subsequently reduced. The OI decreased (by 47±9%) reflecting improved oxygenation at high P_ao levels during HFOV in the Ramp group. However, high P_ao restored retrograde PBF during diastole in 4 of 6 lambs, indicating the restoration of right-to-left shunting through the ductus arteriosus. Thus, the choice of volume recruitment manoeuvre influences the magnitude of change in OI and PBF that occurs during HFOV. Despite significantly improving OI, the ramp recruitment approach causes sustained changes in PBF.