Advances in ventilator technology allowed mechanical breaths to be synchronised with the onset of spontaneous inspiration. This was achieved by using signals derived from spontaneous respiratory activity. Synchronisation was also extended to termination of the positive pressure breath in synchrony with the end of spontaneous inspiration or when inflation is completed. Respiratory signals used for synchronisation have included abdominal wall motion, oesophageal pressure, thoracic impedance, airway pressure and gas flow. The latter is also used to terminate the mechanical breath in a modality known as flow cycling. Measuring gas flow also permits tidal volume (VT) monitoring, which is available in most neonatal ventilators.