Journal of Applied Physiology, Vol 64, Issue 5 2026-2032, Copyright © 1988 by American Physiological Society
Effects of nitroprusside on lung mechanics and hemodynamics after endotoxemia in awake sheep
P. Wright, Y. Ishihara and G. R. Bernard
Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232.
We examined the effects of intravenous sodium nitroprusside (NP) infusion
on pulmonary arterial pressure (Ppa), pulmonary vascular resistance (PVR),
dynamic compliance (Cdyn), resistance to airflow across the lungs (RL), and
alveolar-arterial O2 pressure gradient (PAO2-PaO2) (room air) after
endotoxemia in awake sheep. NP infused 2.5 h after endotoxin administration
immediately reduced mean Ppa from 30 +/- 3 to 17 +/- 3 (SE) cmH2O, PVR from
6.3 +/- 0.7 to 4.8 +/- 0.5 cmH2O.l-1.min, and RL from 340 +/- 48 of base
line to 205 +/- 73% and increased Cdyn from 54 +/- 5 of base line to 80 +/-
14% without affecting PAO2--PaO2. Ppa and lung mechanics returned
immediately to preinfusion levels when NP was stopped. In vitro experiments
with NP showed a dose-dependent relaxation of preconstricted pulmonary
artery and vein, carbachol-preconstricted sheep tracheal strips, and
bronchial rings. We conclude that NP reverses pulmonary hypertension and
lung mechanics abnormalities after endotoxin and that this is due to
effects of NP on airway and vascular smooth muscle. The return of these
abnormalities after NP cessation suggests the continued presence of
vascular and airway-constricting factors late after endotoxin. The lack of
effect of NP on blood oxygenation suggests that deleterious effects on
hypoxic vasoconstriction are offset by improved lung mechanics.
