[beta]-Adrenergic Blockade and Metabo-Chemoreflex Contributions to ExerciseCapacity

• Autores: Sofia Beloka, Marko Gujic, Gael Deboeck, Georges Niset, Agnieszka Ciarka, Jean-françois Argacha, Dionysios Adamopoulos, Philippe van de Borne, Robert Naeije
• Localización: Medicine & Science in Sports & exercise: Official Journal of the American College of Sports Medicine, ISSN 0195-9131, Vol. 40, Nº. 11, 2008, págs. 1932-1938
• Idioma: inglés
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• Resumen

  • Purpose: Exercise-induced dyspnea in patients with cardiopulmonary diseases may be related to sympathetic nervous system activation, with increased metabo- and/or chemosensitivities. Whether this mechanism plays a role in exercising normal subjects remains unclear.

    Methods: Muscle sympathetic nerve activity (MSNA), HR, ventilation (V[spacing dot above]E), O2 saturation (SpO2), and end-tidal PCO2 (PetCO2) were measured in 14 healthy young adults after 1 wk of [beta]1-receptor blockade with bisoprolol 5 mg[middle dot]d-1 versus placebo after a double-blind, placebo-controlled, randomized crossover design. The MSNA and the ventilatory responses to hyperoxic hypercapnia (7% CO2 in O2), [DELTA]V[spacing dot above]E/[DELTA]PetCO2, and isocapnic hypoxia (10% O2 in N2), [DELTA]V[spacing dot above]E/[DELTA]SpO2, and to an isometric muscle contraction followed by a local circulatory arrest (metaboreflex) were determined at rest followed by an incremental cardiopulmonary exercise test.

    Results: Bisoprolol did not change the V[spacing dot above]E and MSNA responses to hypercapnia, hyperoxia, or isometric muscle contraction or ischemia. Bisoprolol decreased maximum O2 uptake (P < 0.05), workload (P < 0.05), and HR (P < 0.0001) andboth V[spacing dot above]E/V[spacing dot above]O2 and V[spacing dot above]E/V[spacing dot above]CO2 slopes (P < 0.05).

    Conclusions: These results suggest that decreased aerobic exercise capacity after intake of [beta]-blockers is accompanied by decreased ventilation at any metabolic rate. However, this occurs without detectable change in the sympathetic nervous system tone or in metabo- or chemosensitivity and is therefore probably of hemodynamic origin.