Journal of Applied Physiology, Vol 54, Issue 6 1477-1481, Copyright © 1983 by American Physiological Society
Active inspiratory impedance in halothane-anesthetized humans
P. K. Behrakis, B. D. Higgs, A. Baydur, W. A. Zin and J. Milic-Emili
We have used the method of Siafakas et al. (J. Appl. Physiol.: Respirat.
Environ. Exercise Physiol. 51: 109-121, 1981) to determine active elastance
(E'rs) and flow resistance (R'rs) of the respiratory system in eight
spontaneously breathing humans anesthetized with halothane. From
measurements of flow (V) and volume (V) during unoccluded inspirations and
of tracheal pressure (P0tr) during subsequent inspirations with the airways
occluded at end expiration, we were able to compute E'rs and R'rs as slopes
and intercepts of the following function: -P0tr/V = R'rs + E'rsV/V. These
measurements were repeated during inspirations loaded with a series of
linear flow resistances (delta R). Neither E'rs nor R'rs was significantly
affected by delta R. On the average E'rs and R'rs were, respectively, 34.4
and 16.7% higher than the corresponding passive elastance and flow
resistance of the respiratory system, indicating that during active
breathing the internal impedance of the respiratory system increases. This
provides an internal mechanism by which passive loads are compensated.
