Validation of mean arterial pressure as an indicator of acute changes in cardiac output.

Changes in mean arterial pressure (MAP) are often assumed to reflect changes in cardiac output (CO). A linear relationship is postulated to exist between these two quantities based upon the circuit model for systemic circulation. Previous studies have correlated changes in CO and MAP. However, to our knowledge, no studies have tested the relationship between CO and MAP in vivo without changes in systemic vascular resistance. Research on baroreceptor stimulation and vasomotor response has shown that vasomotor tone changes 15 to 60 seconds after an acute change in CO. Maximal activation of vasomotor response occurs after approximately 30 seconds. Thus MAP should correlate directly with CO during acute changes (< 15 seconds). To test this, we examined the relationship between CO and MAP during 10 second occlusions of the inferior vena cava in anesthetized pigs. A linear relationship existed between CO and MAP in seven pigs (%MAP = 0.60[%CO] - 0.41, p = 0.0001). This study validates the use of MAP as an indicator of acute changes in CO. Fluctuations in MAP correlate well with acute changes in CO in the absence of changes in vascular tone.