VERTICAL GRADIENT IN REGIONAL VASCULAR RESISTANCE AND PRE TO POST CAPILLARY RESISTANCE RATIOS IN THE DOG LUNG

Abstract

The ratios of pre-capillary (Ra) and post-capillary

(Rv) resistance s to total vascular resistance (R_T)

were measured at different vertical distances in the

lun gs of supine dogs. Capillary pressures were esti-

mated as the algebraic sum of the alveolar absorp-

tion pressure for Tyrode's solution and the plasma

colloid osmotic pressure. Segmental resistance frac-

tions (Ra/ R_T, Rv/ R_T) were calculated using the

pressure drops between arterial, capillary, and venous

pressures at each vertical distance within the lung.

In a second group of animals, total vascular resis-

tance was calculated at each lung level using regional

blood flow as measured by radiolabelled micro·

spheres and the corresponding regional vascular pressures.

The total vascular resistance was lo west in

Zone III portions of the lung, but Ra/Rr and

Rv/ R_T were constant throughout this zo ne (n = 22)

averaging .63 ± .02 (SDI) and .37 ± .02 (SEM, respectively,

resulting in Ra/Rv of 1. 70). Total vascular

resistance increased markedly in Zone II portions

of the lung, but the relative contribution of Ra/ R_T

decreased from .62 ± .07 (SEM ) to .45 ± .05 (S EM).

Thus Ra/Rv decreased from 1.70 to .82 in Zone II.

The absolute values of pre- and post-capillary resis-

tances were lowest in Zone Ill but post-capillary re-

sistance increased to a greater degree than pre-capillary·

resistance up Zone II.