Journal of Applied Physiology, Vol 41, Issue 5 623-630, Copyright © 1976 by American Physiological Society
Effect of inspired volume on closing volume
B. Holtz, B. Bake and H. Oxhoj
Closing volume (CV) was ?EASURED WITH THE RESIDENT GAS TECHNIQUE IN 12
HEALTHY SEATED SUBJECTS AGE 22-70 YR, AND IN 8 SUBJECTS WITH THE BOLUS
TECHNIQUE. Various volumes were inspired (Vi range: 20-100% vital capacity)
from residual volume and CV was assessed on the subsequent recording of
expired volume versus gas concentration. The results indicate that the
resident gas technique may erroneously underestimate CV at reduced Vi in
conformity with calculations which predict that during expiration, after a
certain reduced VI, the nitrogen concentration is identical in the most
basal lung region and at the mouth. CV obtained with the bolus technique
decreased linearly with reduced Vi and the effect appeared to be age
dependent according to the equation CV50/CV100=0.0078 X age +1.18, where
CV50 and CV100 denote the bolus CV corresponding to Vi=50% and 100% of
vital capacity. Therefore, in older subjects, during tidal breathing,
airways appear to close at substantially lower lung volume than previously
considered.
