Relationship of intra-oesophageal pressure to mouth pressure during the measurement of thoracic gas volume in the newborn.

During the measurement of thoracic gas volume, mouth pressure changes were compared to oesophageal pressure changes using an oesophageal balloon system. In individual babies the correlation was high, with r values in excess of 0.98. In other babies the correlation was less satisfactory due to cardiac contractions producing artefacts in the oesophageal pressure trace. The overall correlation obtained from analysing 155 respiratory efforts in a group of 21 babies studied on 23 occasions exceeded an r value of 0.90. We conclude that it is valid to use an oesophageal balloon system to measure changes in intrathoracic pressure.