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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.

The MEFV curve has been analysed for the mechanical time constant distribution through the lungs, and it has been transformed into the forced decay of the thoracic gas volume (FVtD). The best regression formula to express the FVtD was the exponential in respect to the linear one, and this difference was statistically significant only in asthmatic patients. It seems likely that the FVtD will prove to be useful for detecting, already in the simple routine functional investigation, the airways obstruction due to asthma as interlobular inhomogeneity of ventilation.

Airway conductance related to thoracic gas volume (Gs) was measured by body plethysmography in 32 subjects with asthma, before and 10 min after aerosol of beta-adrenergic stimulant (salbutamol, 200 μg). Improvement of conductance (D-Gs) appeared less in cases with either highest or lowest Gs baseline value. Yet D-Gs beared no relationship to Gs, and therefore will not be predictable for any particular case considering Gs alone. D-Gs appeared neither independent nor proportional to Gs.

The changes of ventilatory function during laparoscopy were proved both by spirometry and blood gas measurements. With 32 patients the spirometric data, the thoracic gas volume and the airway resistan