Abstract
Expired Gas Analyzer (Sanei Sokki), which can perform a rapid and continuous recording of the expired gas oxygen concentration, was used for the measurement of “closing volume”. Briefly, the test was done in the following way. Starting from the RV level, the subject breathes at first a bolus of helium (about 300ml), then pure oxygen to the TLC level, after which he expires slowly and steadily (about 200-300ml/sec.) into the circuit. Both expired gas oxygen concentration and volume are recorded and displayed on a storage oscilloscope (Tektronix). Toward the end of the expiration the oxygen concentration drops with the increase of helium mixing in the expired gas, thus forming “Phase IV”. Closing volume (CV), which is defined as the volume between the onset of phase IV and RV, was expressed as a percentage of vital capacity (CV/VC%).
Using this method, CV/VC% was measured in 75 subjects, Thirty-one were normal, nine had chronic obstructive lung disease (emphysema and chronic bronchitis), nineteen had bronchial asthma, and sixteen had various lung diseases including eight cases of heavy smokers.
As reported by others, there was a positive correlation between age and CV/VC% for both normal males and females.
In patients with chronic obstructive lung disease and bronchial asthma, who showed a significant degree of airway obstruction, the slope of the alveolar plateau (phase III) was steep and CV/VC% was increased in most of the cases.
In patients with asymptomatic asthma, whose spirometric studies were either normal or only slightly impaired, the slope of the alveolar plateau was not steep but cardiac oscillations, which were clearly observed in normal subjects, were either absent or insignificant. CV/VC% was increased in three and normal in one, however, there were four patients whose closing volume was unobtainable because of the absence of phase IV.
In all of the heavy smokers, CV/VC% was increased.
It is concluded from these results that our method is applicable for clinical purposes.
