Beta-blockade does not improve orthostatic intolerance induced by 20 days bed rest

Area of Science:

• Cardiovascular Physiology
• Exercise Physiology

Background:

• Prolonged bed rest (BR) induces orthostatic intolerance, a condition affecting cardiovascular regulation.
• Understanding interventions to mitigate BR-induced orthostatic intolerance is crucial for health and recovery.

Purpose of the Study:

• To investigate the efficacy of propranolol in preventing or treating orthostatic intolerance following 20 days of bed rest.
• To assess the impact of propranolol on cardiovascular responses during lower body negative pressure (LBNP) after bed rest.

Main Methods:

• Nine healthy volunteers underwent LBNP tests and echocardiography before and after 20 days of BR, with and without intravenous propranolol.
• Measurements included LBNP tolerance time, heart rate, stroke volume, cardiac output, and systemic vascular resistance changes during LBNP.

Main Results:

• Propranolol decreased endpoint heart rate and systemic vascular resistance but did not alter cardiac output or stroke volume changes during LBNP after BR.
• The drug did not improve LBNP tolerance time, indicating no change in orthostatic intolerance.
• Percentage changes in cardiac output during LBNP were not significantly different with or without propranolol post-BR.

Conclusions:

• Intravenous propranolol administration does not ameliorate orthostatic intolerance induced by prolonged bed rest in healthy individuals.
• The cardiovascular effects of propranolol, such as heart rate reduction, do not translate into improved tolerance to orthostatic stress after bed rest.