The Effect of Long-Term β-Adrenergic Receptor Blockade on the Oxygen Delivery and Extraction Relationship in Patients With Coronary Artery Disease

In Brief PURPOSE We evaluated the effects of long-term β-blocker treatment on the balance between oxygen delivery and extraction at peak oxygen uptake (VO2) and at target heart rate training (anaerobic threshold). METHODS Fifteen patients with coronary artery disease performed paired peak cardiopulmonary and submaximal exercise tests on a cycle ergometer with and without atenolol treatment. Thirty minutes following the submaximal tests, participants pedaled 10 minutes at a workload corresponding to that of the anaerobic threshold attained. Arterial oxygen was defined from echocardiography and venous oxygen content. RESULTS At rest, stroke volume, heart rate, and cardiac output were lower (P < .05), whereas arteriovenous oxygen difference [(a − v)O2] was higher with the use of atenolol (P < .05). At peak exercise, heart rate, lactate, and systolic blood pressure were lower (P < .05), whereas (a − v)O2 was higher (P < .05) with the use of atenolol. At anaerobic threshold, stroke volume, heart rate, cardiac output, and systolic blood pressure were lower (P < .05), whereas (a − v)O2was higher (P < .05) with the use of atenolol. Absolute VO2 and workload during maximal (P = .67 and P = .49, respectively) and submaximal (P = .13 and P = .44, respectively) exercises were similar between conditions. CONCLUSIONS Results demonstrate that atenolol treatment in patients with coronary artery disease does not alter VO2 and workload at the anaerobic threshold and peak exercise because of an increase in oxygen extraction and stroke volume in the face of reduced heart rate. These findings indicate that with long-term β-adrenergic receptor blockade, there is interplay between oxygen delivery and extraction, suggesting a link between cardiac hemodynamic responses and skeletal muscle metabolic adaptations. This study investigated the oxygen delivery—extraction relationship at the anaerobic threshold and at peak aerobic exercise in patients with coronary artery disease with and without long-term β-adrenergic receptor blockade. Findings indicate that long-term β-adrenergic receptor blockade does not alter overall oxygen uptake because of an interplay between oxygen delivery and oxygen extraction.