Journal of Applied Physiology, Vol 57, Issue 1 254-261, Copyright © 1984 by American Physiological Society
Effect of regional inhomogeneity on collateral airway resistance
S. D. Fuller and N. E. Robinson
We studied the interaction of transpulmonary pressure (Pao) and the
pressure in an isolated sublobar lung segment (Ps) on collateral resistance
(Rcoll) in excised dog lungs. A double-lumen catheter was advanced through
the trachea and wedged in a peripheral airway. Gas flowed through the outer
lumen of the catheter (Vcoll) to enter the segment while Ps was measured by
the inner lumen. Collateral resistance was calculated as Rcoll = (Ps -
Pao)/Vcoll. At constant Ps, raising Pao sharply decreased Rcoll, but at
constant Pao, raising Ps increased Rcoll. Replotting these data showed that
Rcoll was related to the pressure difference between the segment and the
remainder of the lobe (Ps - Pao), such that raising Ps - Pao caused no
change in Rcoll at lower Pao but increased Rcoll at higher Pao. Similar
findings occurred in the lungs of closed-chest anesthetized dogs. We
propose that this technique measures the sum of resistances of airways and
collateral channels found in the segment body (Rs) and of those passing
through the segment-lobar parenchymal interface (Ri). Raising Ps - Pao
decreases Rs because of the volume dependency of airway resistance and
increases Ri due to tissue distortion at the interface occurring as a
result of inhomogeneous segment inflation. The net change in measured Rcoll
depends on which of its components change in greatest magnitude. This
effect varies with Pao due to the hyperbolic relationship of Pao with
airway and collateral resistance.
