Pulmonary gas exchange effects of nitroglycerin in canine edematous lungs

The authors determined the effects of nitroglycerin on pulmonary edema induced by oleic acid injury. Measurements of venous admixture (QVA/Qt) and shunt (Qs/Qt) using both oxygen and inert-gas-elimination methods were done before, during, and after nitroglycerin infusion, first during air ventilation and then during ventilation with 100 per cent oxygen. Nitroglycerin reduced mean blood pressure (MAP) approximately 30 per cent (P less 0.01) during both air and oxygen ventilation. During air ventilation, nitroglycerin caused PVR to decrease by 29 per cent (P less than 0.01) but caused no change in PVR during oxygen ventilation. Pa02 decreased from 64 +/- 8 torr (mean +/- SD) to 55 +/- 9 torr (P less than 0.01) with nitroglycerin infusion during air ventilation. The decrease in Pa02 was primarily due to an increase in QVA/Qt which increased from 28 +/- 12 per cent to 36 +/- 14 per cent (oxygen method) (P less than 0.05). Similarly, the inert gas QVA/Qt increased from 31 +/- 10 to 37 +/- 14 per cent (P less than 0.05). During oxygen ventilation, the effect of nitroglycerin on gas exchange was similar in direction but less in magnitude. These results provide evidence that nitroglycerin may cause significance impairment of pulmonary gas exchange when abnormal lung function is present and FI02 is low. The mechanism is most likely due to inhibition of hypoxic pulmonary vasoconstriction.