Journal of Applied Physiology, Vol 38, Issue 1 64-69, Copyright © 1975 by American Physiological Society
Role of inertia in the measurement of dynamic compliance
J. Dosman, F. Bode, J. Urbanetti, R. Antic, R. Martin and P. T. Macklem
Dynamic compliance (Cdyn) was measured at different frequencies
(breaths/min) in 30 nonsmoking males and females aged 30-59 yr. In those
aged 30-49 yr Cydn at 90 breaths/min was significantly higher than at 15
breaths/min while those aged 50-59 yr showed no significant difference.
Assuming an inertance of 0.01 cmH2O/l per s-2, and a sinusoidal breathing
frequency, Cydn at 60 and 90 breaths/min was corrected for inertia. In the
30-49 yr age group corrected Cydn did not change with increasing frequency
of breathing whereas in the 50-59 yr age group Cydn at 15 breaths/min was
significantly higher than at 90 breaths/min (P is less than 0.05). In this
age group, four of eight subjects were frequency dependent when corrected
for inertia. These findings indicate that inertia influences Cydn at
breathing frequencies of 60 per min and above. Unless this is taken into
account, frequency dependence of compliance may be missed. The results also
indicate that frequency dependence of compliance is normal in some older
individuals but is not normal in the younger age group.
