Tissue acidosis: role in sustained arteriolar dilatation distal to a coronary stenosis. Circulation

This study tested the hypothesis that myocardial tissue acidosis is responsible for maintenance of reduced arteriolar tone distal to a severe coronary arterial stenosis. Domestic swine (n=10) were instrumented with a coronary arterial stenosis that reduced vessel diameter 80%. Measurements of hemodynamic indexes were made 1) before stenosis, 2) at 5, 20, and 60 minutes after stenosis placement, and 3) after each of three, 20-minute NaOH infusions (0.05 M, 0.1 M, and 0.5 M) distal to the stenosis (group 1). Intracellular pH at the end of 30 minutes of 0.5 M NaOH infusion distal to the stenosis was measured in a second group (n=6) of swine (group 2). After stenosis placement in group 1, endocardial blood flow declined significantly, and evidence of regional acidosis (increased coronary venous Pco2 and decreased coronary venous pH) and ischemia (lactate production) developed. One hour later, evidence of acidosis persisted, though to a lesser extent. Myocardial oxygen and lactate metabolism exhibited similar patterns. Infusion of 0.5 M NaOH (0.38 ml/min) reduced (p < 0.01) distal zone epicardial blood flow but did not change endocardial flow. Regional myocardial oxygen extraction (75 ±8%, mean+SD) and consumption (8.2+±2.3 ml/min/100 g) also declined significantly (p<0.01) in response to 0.5 M NaOH infusion compared with 60 minutes after stenosis (86±4 and 12.4+2.