AJP - Heart and Circulatory Physiology, Vol 241, Issue 5 732-H739, Copyright © 1981 by American Physiological Society
Estimates of isogravimetric capillary pressures during alveolar hypoxia
R. E. Parker, D. N. Granger and A. E. Taylor
Isogravimetric capillary pressures (Pci) and pre-(Ra) and postcapillary
(Rv) pulmonary vascular resistances were estimated in isolated dog lungs
when ventilated with 95% O2-5% CO2 and during alveolar hypoxia, which was
simulated by ventilation with a 95% N2-5% CO2 gas mixture. In addition, the
filtration coefficient (KF,C) was measured during alveolar hypoxia and
compared with prehypoxic measurements. When both arterial and venous
pressures were maintained constant during the alveolar hypoxia, Pci
decreased from 8 to 6.9 mmHg, and total pulmonary vascular resistance
increased from 0.040 to 0.083 (cmH2O . ml-1 . min . 100 g lung). Ra
increased significantly from 0.027 to 0.067, and Rv remained unchanged,
averaging 0.013 and 0.015 for control and hypoxic conditions, respectively.
The changes in vascular resistance observed in alveolar hypoxia appear to
be confined to blood vessels that are probably located in larger preseptal
blood vessels. KF,C increased significantly from 0.092 to 0.179 ml . min-1
. cmH2O-1 . 100 g lung-1 during hypoxia. Either the surface area available
for fluid exchange or the vascular permeability increases with alveolar
hypoxia in the isolated dog lung. Inasmuch as vascular pressures were
maintained constant in the present study, then the increase in KF,C with
alveolar hypoxia is probably associated with changes in vascular
permeability rather than an increased surface area of the fluid exchange
vessels.
