Muscle metaboreflex-induced increases in stroke volume

PURPOSE: Accumulation of by-products of metabolism within skeletal muscle may stimulate sensory nerves, thus evoking a pressor response named muscle metaboreflex. The aim of this study was to evaluate changes in central hemodynamics occurring during the metaboreflex activation. METHODS: In seven healthy subjects, the metaboreflex was studied by postexercise regional circulatory occlusion at the start of the recovery from a mild rhythmic forearm exercise. Central hemodynamics was evaluated by means of impedance cardiography. RESULTS: The main findings of this study were that, with respect to rest, the metaboreflex: 1) raised mean blood pressure (+13%; P < 0.01); 2) enhanced myocardial contractility (-12% in preejection period/left ventricular ejection time ratio; P < 0.01); 3) prolonged diastolic time (+11%; P < 0.01); 4) increased stroke volume (+ 10%; P < 0.05); and 5) increased cardiac output (+6%; P < 0.05). These responses were present neither during recovery without circulatory occlusion nor during circulatory occlusion without prior exercise. Moreover, the metaboreflex did not affect systemic vascular resistance and induced bradycardia with respect to recovery without circulatory occlusion. CONCLUSION: These results suggest that the blood pressure response during metaboreflex activation after mild rhythmic exercise is strongly dependent on the capacity to increase cardiac output rather than due to increased vascular resistance.