Pulmonary Gas Exchange Effects of Nitroglycerin in Canine Edematous Lungs

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Abstract
The effects were determined of nitroglycerin on pulmonary gas exchange in 11 anesthetized dogs with diffuse pulmonary edema induced by oleic acid injury. Measurements of venous admixture (.ovrhdot.QVA/.ovrhdot.Qt) and shunt (.ovrhdot.QS/.ovrhdot.Qt) using both O2 and inert-gas-elimination methods were done before, during and after nitroglycerin infusion, 1st during air ventilation and then during ventilation with 100% O2. Nitroglycerin reduced mean blood pressure (MAP) .apprx. 30% (P < 0.01) during both air and O2 ventilation. During air ventilation, nitroglycerin caused PVR [pulmonary vascular resistance] to decrease by 29% (P < 0.01) but caused no change in PVR during O2 ventilation, Pa[arterial partial pressure]O2 decreased from 64 .+-. 8 torr (mean .+-. SD) to 55 .+-. 9 torr (P < 0.01) with nitroglycerin infusion during air ventilation. The decrease in PaO2 was primarily due to an increase in .ovrhdot.QVA/.ovrhdot.Qt which increased from 28 .+-. 12% to 36 .+-. 14% (O2 method) (P < 0.05). Similarly, the inert gas .ovrhdot.QVA/.ovrhdot.Qt increased from 31 .+-. 10 to 37 .+-. 14% (P < 0.05). During O2 ventilation, the effect of nitroglycerin on gas exchange was similar in direction but less in magnitude. Nitroglycerin may cause significant impairment of pulmonary gas exchange when abnormal lung function is present and FIO2 [fractional concentration of O2 in inspired air] is low. The mechanism is most likely due to inhibition of hypoxic pulmonary vasoconstriction.