Critical assessment of jacket plethysmographs for use in young children.

In infants and very young children changes in thoracic gas volume (Vtg) during tidal breathing and during intermittent positive-pressure lung inflations have been estimated from pressure changes within double-layered rubber jackets covering the thorax and abdomen. In vitro and in vivo assessments demonstrated the linearity of these jackets over the range of volume changes found in these young subjects during respiratory function tests, and the small intrajacket background pressure (2.5 cmH2O) had minimal effects on resting lung volume and lung mechanics. These jackets can be used to monitor tidal volume in quiet subjects, and if an intermittent positive-pressure inflation technique is used static compliance can be accurately measured. The hysteresis of natural rubber and the direct contact of the recording system with the subject renders it unsuitable for the measurement of lung mechanics during tidal breathing and for the estimation of Vtg during airway occlusions.