Inclusion Criteria: The patient must be scheduled for elective surgery where spontaneous breathing and physical access to the chest during surgery are feasible  The patient must require general anaesthesia The parents are able to give informed consent for inclusion in the study  Exclusion Criteria:  The patient is mechanically ventilated before start of the study. The patient is not anticipated to breathe spontaneously for a substantial amount of time prior to emergence from anesthesia The patient is known or suspected to have an anatomical malformation or surgical correction of the diaphragm.  The patient suffers from a disease that may impair diaphragmatic function:  Central neural disease at the level of the brain (Stroke, Arnold-Chiari malformation) and spinal cord (quadriplegia, spinal muscular atrophy, syringomyelia). Neural disease of the phrenic nerve (Guillain-Barré syndrome, tumor compression). Disorders of the neuromuscular junction. Muscular diseases (muscular dystrophies, myositis (infectious, inflammatory, metabolic).