Lactic acidosis and the cardiovascular system in the dog.

1. Lactic acidosis is a clinical syndrome characterized by metabolic acidaemia (pH less than 7.25) and hyperlactaemia (lactate greater than 5 mmol/l). Many patients with type B lactic acidosis have no evidence of tissue hypoxia or myocardial dysfunction when first evaluated. Although it is considered that cardiac dysfunction is secondary to the systemic effects of lactic acidosis, the reverse may sometimes be true. To evaluate this possibility, studies were carried out in 43 dogs consisting of a control group and three groups which had hyperlactataemia and metabolic acidaemia related to either: (1) phenformin infusion; (2) hepatectomy; (3) lactic acid infusion. Serial studies of cardiac function, as well as measurements of GFR (glomerular filtration rate) and hepatic portal vein (HPV) blood flow, were carried out. 2. In dogs infused with phenformin for 99 min, the arterial pH, lactate, bicarbonate, heart rate and mean blood pressure (BP) were normal. However, there was significant deterioration (P less than 0.01) in several indices of cardiac function, including the peak positive dP/dt, cardiac output, LVEDP (left ventricular end-diastolic pressure) and percentage extraction of oxygen and lactate by the heart. After 3 h of phenformin, the blood lactate exceeded 5 mmol/l and there were further significant decrements (P less than 0.01) in cardiac output, LVEDP and dP/dt, as well as BP and heart rate. In dogs subjected to hepatectomy, the decrement in cardiac output was similar to that with phenformin infusion. However, in animals infused with lactic acid, despite a similar blood pH and lactate, cardiac output was unaffected. Although percentage myocardial oxygen extraction declined in phenformin-infused animals, there was a concomitant increase in coronary sinus blood flow such that myocardial oxygen utilization was probably unaltered. 3. Thus, in certain types of experimental type B lactic acidosis, myocardial dysfunction may be a primary event, with other associated systemic manifestations being secondary.