Influence of arterial oxygen tension on coronary vasodilator action of nitroglycerine

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Abstract
In 11 anesthetized open-chest dogs, controlled perfusion of the left circumflex coronary artery was accomplished by shunting blood from the femoral artery and vein via a peristaltic pump. The pO2 of the perfusing blood was altered by changing the proportion of arterial and venous blood reaching the inflow side of the pump. Coronary perfusion pressure (CPP) was measured during stepwise reduction in the left circumflex coronary flow (LCF) over the range 120–10 cc/min. Resistance to coronary blood flowin the perfused myocardial segment was calculated as the ratio CPP/LCF and plotted against flow. Resistance-flow curves for the perfused coronary segments were obtained at pO2 values ranging between 95 and 25 mm Hg. Lowering the pO2 of the perfusing blood caused a reduction in coronary vascular resistance (CVR) in the perfused segment. When nitroglycerine was infused in a dosage of 3–6 μg/kg per minute, arterial blood pressure and heart rate were unaltered but CVR was reduced. The reduction in CVR was inversely proportional to the pO2 of the perfusing blood, the maximal vasodilator effect being observed at pO2 > 60 mm Hg. Nitroglycerine caused no significant change in coronary vascular resistance at pO2 < 39 mm Hg and did not prevent or delay the appearance of excess lactate in the coronary venous blood.

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