Some infants with breathing problems at birth may need to be connected to a machine to help support their breathing. The purpose of this study is to optimise the level of breathing support on Bi level continuous airway pressure (BiPAP), a support which gives two levels of support (pressure) to premature infants. The study is investigating which upper pressure gives the best support, that is results in the baby having to breathe less hard (work of breathing). Researchers will measure the work of breathing using a small catheter. Infants will receive three different upper pressures of BiPAP with the same baseline pressure for 20 minutes each. In between each upper level they will receive the standard upper pressure for 20 minutes.