Esmolol acutely alters oxygen supply-demand balance in exercising muscles of healthy humans.

Beta-adrenoreceptor antagonists (β blockers) reduce systemic O delivery and blood pressure (BP) during exercise, but the subsequent effects on O extraction within the active limb muscles are unknown. In this study, we examined the effects of the fast-acting, β selective blocker esmolol on systemic hemodynamics and leg muscle O saturation (near infrared spectroscopy, NIRS) during submaximal leg ergometry. Our main hypothesis was that esmolol would augment exercise-induced reductions in leg muscle O saturation. Eight healthy adults (6 men, 2 women; 23-67 year) performed light and moderate intensity bouts of recumbent leg cycling before (PRE), during (β -blocked), and 45 min following (POST) intravenous infusion of esmolol. Oxygen uptake, heart rate (HR), BP, and O saturation (SmO ) of the vastus lateralis (VL) and medial gastrocnemius (MG) muscles were measured continuously. Esmolol attenuated the increases in HR and systolic BP during light (-12 ± 9 bpm and -26 ± 12 mmHg vs. PRE) and moderate intensity (-20 ± 10 bpm and -40 ± 18 mmHg vs. PRE) cycling (all P < 0.01). Exercise-induced reductions in SmO occurred to a greater extent during the β -blockade trial in both the VL (P = 0.001 vs. PRE) and MG muscles (P = 0.022 vs. PRE). HR, SBP and SmO were restored during POST (all P < 0.01 vs. β -blocked). In conclusion, esmolol rapidly and reversibly increases O extraction within exercising muscles of healthy humans.