Midodrine prevents orthostatic intolerance associated with simulated spaceflight

Area of Science:

• Space medicine
• Cardiovascular physiology
• Pharmacology

Background:

• Astronauts frequently experience orthostatic intolerance (OI) after spaceflight, characterized by hypotension and presyncope upon assuming an upright position.
• OI poses risks during spacecraft reentry and emergency egress, particularly after long-duration missions and for future interplanetary exploration.
• Current countermeasures for OI are not fully effective, highlighting the need for novel therapeutic strategies.

Purpose of the Study:

• To investigate the efficacy of alpha-adrenergic stimulation as a countermeasure for orthostatic intolerance.
• To test the hypothesis that the alpha(1)-agonist midodrine can prevent post-flight orthostatic intolerance.

Main Methods:

• A 16-day head-down-tilt bed-rest study was conducted as an analog for weightlessness.
• Normal human volunteers received midodrine at the conclusion of the bed-rest period.
• A provocative tilt test was administered to assess cardiovascular responses.

Main Results:

• Midodrine administration significantly attenuated excessive decreases in blood pressure during the tilt test.
• The drug effectively reduced the incidence of presyncope in participants.
• These findings demonstrate a clear physiological benefit of midodrine in mitigating OI symptoms.

Conclusions:

• Midodrine shows promise as an effective countermeasure for preventing orthostatic intolerance after spaceflight.
• Alpha-adrenergic stimulation may be a key therapeutic target for managing spaceflight-induced cardiovascular deconditioning.
• Further research is warranted to optimize midodrine dosage and administration protocols for astronauts.