| Research Abstract |
Muscle capillary 02 partial pressure (PO2) has been found to reach a minimal value, i.e., a critical capillary P02 in the midrange of the work capacity in patients with cardiovascular disease. However, it is not known if the critical capillary 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 flow response to exercise, using low-dose infusion of dobutamine, on muscle end-capillary PO2 (as approximated by femoral vein PO2), lactate concentration, O2 uptake (VO2), and the relation among these variables. We also evaluated the effects of physical training on these relations in patients with heart failure. Eleven male patients with coronary artery disease performed an incremental exercise test on a cycle ergometer with and without continuous infusion of dobutamine (6μg/kg/min). Six patients with heart failure also performed exercise testing before and 3 months after physical training. Respiratory ga
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s analysis was performed on a breath-by-breath basis ; femoral vein blood was sampled every minute through a percutaneous catheter during exercise testing. Dobutamine increased resting VO2 and VO2 at the lactic acidosis threshold (LAT) but not peak V02. The femoral vein PO2 rapidly decreased toward a minimal value with increasing work rate (VO2) irrespective of the infusion of dobutamine. After reaching its nadir (critical PO2), femoral vein lactate began to increase without further decrease in PO2.Infusion of dobutamine significantly increased femoral vein resting (27.4±4.9 vs 32.5±3.8 torr) and critical PO2 (20.5±1.5 vs 21.9±1.7 torr), but not the PO2 at peak V02 (22.1±3.3 vs 22.0±2.9 torr). In 4 patients out of 5 patients who performed physical training, both exercise capacity and critical PO2 were increased, suggesting increased blood flow to the exercising muscle. ltwas found that both infusion of dobutamine and physical training raise the critical PO2 in exercising muscles. These findings suggest that the increase in blood flow benefits exercising muscle by increasing capillary P02, thereby delaying the onset of lactic acidosis. Less
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