Augmentation of hypoxic pulmonary vasoconstriction by NG-L-methyl-arginine in a rabbit model of thermal injury

We tested deeply anesthetized rabbits to determine if a burn acutely diminished the strength of hypoxic pulmonary vasoconstriction (HPV) and if this could be augmented by L-NMMA, a nitric oxide synthase inhibitor. We induced a burn using water heated to 75°C and assessed the strength of HPV as the difference in pulmonary vascular resistance during 100% and 13% O2 ventilation. The rabbits then were randomized to receive 10 mg/kg L-NMMA (n = 8) or a placebo (n = 8). The strength of HPV decreased from 0.42 ± 0.11 mm Hg/mL/min preburn to 0.22 ± 0.11 mm Hg/mL/min postburn (P< .05). L-NMMA administration augmented HPV to a postburn value of 0.48 ± 0.014 mm Hg/mL/min (P< .05). We speculate that the loss of HPV following a burn could worsen ventilation to perfusion mismatch and thereby aggravate the hypoxia associated with burns. Augmentation of HPV might be a short-term goal during the acute stabilization of hypoxic burn patients.