Propranolol and inspiratory muscle performance in normal subjects

Area of Science:

• Respiratory Physiology
• Exercise Physiology
• Pharmacology

Background:

• Beta-adrenergic blockade is known to affect exercise performance.
• The impact of propranolol on respiratory muscle function during loaded breathing is not fully understood.

Purpose of the Study:

• To investigate the effects of propranolol on respiratory muscle performance and endurance during inspiratory threshold-loaded breathing in healthy individuals.
• To explore the mechanism behind any observed changes in respiratory muscle function.

Main Methods:

• Eight healthy subjects participated in the study.
• Subjects received propranolol (mean dose 160 mg/day).
• Respiratory muscle performance was assessed using maximal voluntary ventilation (MVV) and maximal sustainable ventilatory capacity (MSVC) during inspiratory threshold loading. Maximal static inspiratory and expiratory pressures were also measured.

Main Results:

• Propranolol significantly reduced loaded 15-second MVV and MSVC.
• Maximal static inspiratory pressures were decreased at certain lung volumes.
• Four subjects reported symptoms of tiredness and fatigability, and their reduced inspiratory muscle performance accounted for the overall population effect. This effect was independent of propranolol dose, beta-receptor blockade, or physical fitness.

Conclusions:

• Propranolol can directly impair inspiratory muscle strength and endurance in individuals experiencing drug-induced fatigue.
• The mechanism appears unrelated to beta-adrenergic-receptor blockade.
• These findings highlight a potential side effect of propranolol on respiratory function in susceptible individuals.