Mechanical ventilation (MV) is life saving for infants requiring respiratory support in the newborn period but its use has been associated with complications. High frequency oscillation (HFO) is a type of MV that delivers small volumes of gas across the lungs at fast frequencies. HFO is a lung protective strategy but it has also been linked to brain injury due to low carbon dioxide tensions. High-frequency oscillation with volume-targeted ventilation (HFO\&VTV) is a new mode of HFO in which the clinician sets a target volume of gas to be delivered to the lungs at fast rates to decrease the lung injury related to the ventilator. Further, HFO\&VTV achieves better control of carbon dioxide levels and may therefore protect against brain injury. Currently, there are no written guidelines about the use of HFO\&VTV. This study aim to determine the safety profile of HFO\&VTV compared to HFO by comparing the velocity of blood flow to the brain in term born infants and the cardiac output in term and preterm infants during the two modes. The investigators will also determine the optimum starting value of the target tidal volume during HFOV\&VTV. Infants will be studied at three different target tidal volumes for a period of 10-20 minutes each. A cranial ultrasound (for term infants only) and bedside echocardiogram will be performed at the end of each period.