Individual lung blood flow during unilateral hypoxia: effects of inhaled nitric oxide

We hypothesized that the diversion of blood away from a hypoxic lung to the opposite oxygenated lung can be enhanced by inhaling nitric oxide (NO) into the oxygenated lung. We measured individual lung blood flow when 50 ppm NO was selectively inhaled to: a hyperoxic lung during contralateral hypoxia; a normoxic lung during bilateral normoxia; and a hyperoxic lung during bilateral hyperoxia. Twenty two patients with healthy lungs were studied during intravenous anaesthesia. The lungs were separately and synchronously ventilated. The relative perfusion of each lung was assessed by the inert gas elimination technique. Unilateral hypoxic (inspiratory oxygen fraction (FI,O2) 0.05) ventilation during contralateral hyperoxia reduced the perfusion of the hypoxic lung from a mean (SD) of 47 (9)% of cardiac output (Q'), to 30 (7)% (p<0.001) of Q'. NO inhalation to the hyperoxic lung increased its blood flow from 70 (7)% to 75 (6)% (p<0.05) of Q', and reduced the blood flow to the hypoxic lung to 25 (6)% (p<0.05). Unilateral NO inhalation during bilateral normoxia or hyperoxia had no effect on pulmonary blood flow distribution. Nitric oxide inhalation to a hyperoxic lung increases the perfusion to this lung by redistribution of blood flow if the opposite lung is hypoxic.