Microsphere reference flow samples during systemic flow adjustment.

Regional myocardial blood flow measurements in the right heart bypass preparation can be particularly valuable, since this preparation provides control of the main hemodynamic determinants of coronary blood flow. We examined the validity of aortic reference flow samples in relation to coronary samples during continuous systemic flow adjustment for aortic pressure control in six dogs on right heart bypass, anesthetized with chloralose and urethan. Microsphere concentrations were compared in paired reference flow samples drawn from the aortic arch and from a coronary artery for 119 left atrial microsphere injections. During left subclavian artery infusion and during femoral artery infusion at rates above 2,000 ml/min, there were high percentage errors in microsphere concentration between paired samples, consistent with aortic sample dilution by systemically infused blood. In 52 injections during withdrawal or femoral infusion below 2,000 ml/min, at cardiac outputs of 390-4,800 ml/min, the percentage error was 0.001 +/- 1.18% (SE); the absolute value of this error was below 20% in 96%, and below 10% in 77% of these injections. Linear regression related these coronary to aortic microsphere concentrations by the equation Y = 1.005X - 1.64, r = 0.997, Sy.x = 13.2 (5.9%). (Sy.x represents the standard deviation from regression.) These data indicate that valid aortic reference flow samples can be obtained within specific hemodynamic conditions during systemic flow adjustment in the right heart bypass preparation.