Barometric plethysmograph: advantages and limitations in recording infant respiration

The barometric plethysmograph enables recordings to be made of respiration in undisturbed unrestrained infants. Its use has been limited by practical difficulties and errors in calculation of tidal volume (VT). We describe a modification of the method that overcomes the practical difficulties and a series of studies in which the barometric method was directly compared with pneumotachograph measurements of VT in infants. The effects of respiratory pattern and expired air temperature plus the most appropriate formula for calculation of VT under different conditions are described.