Effects of dobutamine on critical capillary Po-2 and lactic acidosis threshold in patients with cardiovascular disease

Back-ground. Muscle capillary PO2 has been found to reach a minimal value, ie, a critical capillary PO2, in the midrange of work capacity in patients with cardiovascular disease. However, it is not known if the critical capil lary PO2 can be influenced by a change in blood flow response to exercise. This study was carried out to determine the effect of changing the blood fl ow response to exercise, using low-dose infusion of dobutamine, on muscle e nd-capillary PO2 (as approximated by femoral vein PO2), lactate concentrati on, oxygen uptake ((V)over dot O-2), and the relation among these variables . Methods: Eleven male patients with coronary artery disease performed an inc remental exercise test on a cycle ergometer with and without continuous inf usion of dobutamine, 6 mug/kg/min. Respiratory gas analysis was performed o n a breath-by-breath basis; femoral vein blood was sampled every minute thr ough a percutaneous catheter. Results: Dobutamine increased resting (V)over dot O-2 and (V)over dot O-2 a t the lactic acidosis threshold (LAT) but not peak (V)over dot O-2. The fem oral vein PO2 rapidly decreased toward a minimal value with increasing work rate (V)over dot O-2 irrespective of the infusion of dobutamine. After rea ching its nadir (critical PO2), femoral vein lactate began to increase with out further decrease in PO2. Infusion of dobutamine significantly increased femoral vein resting PO2 (27.4 +/- 4.9 nun Hg vs 32.5 +/- 3.8 mm Hg) and c ritical PO2 (20.5 +/- 1.5 mm Hg vs 21.9 +/- 1.7 mm Hg), but not the PO2 at peak (V)over dot O-2 (22.1 +/- 3.3 mm Hg vs 22.0 +/- 2.9 mm Hg). Conclusions: Infusion of dobutamine was found to raise the critical PO2 and LAT but not peak (V)over dot O-2. These findings suggest that some of the acute increase in blood flow induced by dobutamine infusion benefits exerci sing muscle by increasing capillary PO2, thereby delaying the onset of lact ic acidosis.