Beta-adrenergic blockade and metabo-chemoreflex contributions to exercise capacity

Area of Science:

• Cardiopulmonary exercise physiology
• Autonomic nervous system function

Background:

• Exercise-induced dyspnea in cardiopulmonary diseases may involve sympathetic nervous system activation and altered sensitivities.
• The role of these mechanisms in healthy individuals during exercise is not well understood.

Purpose of the Study:

• To investigate the effect of beta1-receptor blockade on sympathetic nerve activity and ventilatory responses during exercise in healthy adults.
• To determine if beta-blockers alter metabo- or chemosensitivity in healthy individuals.

Main Methods:

• A double-blind, placebo-controlled, randomized crossover study involving 14 healthy adults.
• Measurements included muscle sympathetic nerve activity (MSNA), heart rate (HR), ventilation (V(E)), O2 saturation (SpO2), and end-tidal PCO2 (PetCO2).
• Responses to hypercapnia, hypoxia, and isometric muscle contraction with circulatory arrest (metaboreflex) were assessed at rest and during incremental exercise after 1 week of bisoprolol or placebo.

Main Results:

• Bisoprolol did not alter MSNA or ventilatory responses to hypercapnia, hypoxia, or isometric exercise.
• Bisoprolol significantly decreased maximum oxygen uptake, workload, and heart rate.
• Ventilatory efficiency (V(E)/VO2 and V(E)/VCO2 slopes) was reduced with bisoprolol treatment.

Conclusions:

• Beta-blocker intake in healthy individuals reduces aerobic exercise capacity.
• This reduction is associated with decreased ventilation relative to metabolic rate.
• The findings suggest that hemodynamic alterations, rather than changes in sympathetic tone or metabo-/chemosensitivity, likely explain the reduced exercise capacity.