Abstract
The purpose of this paper is to report on a more stable and accessible constant pressure type body plethysmograph than the usual one and normal values of airway resistance in healthy adults measured by this apparatus.
Though the body plethysmograph is essentially a very useful apparatus for measuring airway resistance or thorocic gas volume, several difficalties including complicated handling, expensiveness, disadvantage of the phase lag and the limited frequency responce have prevented its wide use.
In view of this fact, a newly devised constant pressure type body plethysmograph was constructed and tested.
A rigid-walled, airtight box (550 litters) was open to the atmospheric air through a pneumotachograph. Volume changes in the box were recorded as flow changes from the box by the pneumotachograph, and then flow changes integrated to volume changes of the box.
Feeding the pressure signals into mixing circuit, the volume changes of the box were compensated.
Volume changes in the box-pneumotochograph system with volume calibrator were tested. Fluctuation of amplitude ratio of volume-in to volume-out was within 5% in the range from 2.5Hz to 3.5Hz, and no phase distortion was observed in the range from 0.5Hz to 4. 5Hz.
Airway resistance ware measured by this apparatus in twenty healthy nonsmokers. Eight males of age 21 to 36 had mean value of 1.40 ± 0.32 cm/H2O/L/sec and tweleve females of age 20 to 33 had mean value of 1.87 ± 0.37cmH2O/L/sec, which was significantly higher than that in males (p< 0.025).
