Cerebral haemodynamic effects of changes in positive end expiratory pressure in the preterm infant : D.B. Shortlanda, D. Fielda, N.A. Gibsona, K.L. Woodsb, D.H. Evansc and M.I. Levenea. aDepartment of Child Health, bDepartment of Pharmacology and cDepartment of Medical Physics, Leicester University Medical School, Leicester, U.K.