Clinical Assessment of Closing Volume Measurement

Abstract

Closing volumes were studied to assess it's clinical application.
Firstly, physiologicalfactorsinfluencing closing volumes were examined in ten healthy subjects by measuring simultaneous expired volume-concentration curves of N₂ with two of Ar, He, or SF₆. There were no differences in closing volumes measured by Ar, He, or SF₆bolus. Although there existed a bolus volume at which the onset of phase IV was not detected but identified by resident N₂ method, closing volumes decreased as bol us volume is increased. Furthermore, the closing volumes measured by bolus volume of 15% VC was consistently larger than that measured simultaneously by resident-N₂ method.
We found that a expired flow rate above 0.5l/sec could obscure a clear onset of phase 4, and that any marked changes in flow rate above 0.5l/sec would alter the gas concentrations. For clinical applications, then, we propose that the expiratory flow rate be kept constant and less than 0.5l/sec.
Secondly, the relationships between closing volumes andother lung function parameters were studied in ten healthy subjects and thirteen patients. Most of parameters relating to airway obstructive changes were correlated with closing volumes and closing capacities. Parameters with |r|∨0.5 are listed below.
CC% correlated with FEV₁% (r=-0.77), V₂₅(-0.76), V₅₀(-0.67), R_L(+.66), RV% Pa_O2(-0.54). CV% correlated with V₂₅(r=-0.51) 1nd RV% (+0.53).
Finally, in 282 pupils aged from 7 to 15, CV% was measured together with FEVand the V-V curve to assess it's suitability for mass screening. The subjects two different groups. One was the Onahama group who lived in an industrial area andhad respiratory symptoms, the other wasrthe Uchigo control group who lived in a non-industral town and were selected at random to fit the Ohahama population.
In both groups. the incidence of abnormal CV% was higher than the incidence of abnormal FEV₁%. Between the two groups there was no difference in the percentage of abnormal FEV₁%. However, the Onahama group showed a significantly higher percentage of abnormal CV% than than the Uchigo group (p<0.01).
This suggests that closing volume measurements might be suitable for mass screening for early small airway obstruction.