Head-down-tilt bed rest alters forearm vasodilator and vasoconstrictor responses

Area of Science:

• Cardiovascular Physiology
• Human Physiology
• Space Medicine

Background:

• Head-down-tilt bed rest (HDBR) is a model for microgravity exposure.
• Understanding vascular adaptation to HDBR is crucial for astronaut health.
• Previous research suggests potential alterations in vascular function during simulated weightlessness.

Purpose of the Study:

• To investigate the effects of 14-day HDBR on vascular reactivity.
• To assess changes in forearm blood flow (FBF) responses to vasodilatory and vasoconstrictor stimuli.
• To determine if HDBR alters the interplay between vascular dilation and constriction.

Main Methods:

• Utilized head-down-tilt bed rest (HDBR) for 14 days in human participants.
• Measured reactive hyperemic forearm blood flow (RHBF) using venous occlusion plethysmography.
• Assessed mean arterial pressure (MAP) via Finapres and calculated vascular conductance (VC).
• Employed a cold pressor test (CPT) to evaluate vasoconstrictor response and interaction with RHBF.

Main Results:

• Post-HDBR, peak RHBF and VC were significantly reduced compared to pre-HDBR.
• Total excess RHBF over 3 minutes was diminished after HDBR.
• The blunting effect of the CPT on FBF was less pronounced post-HDBR, despite similar MAP increases.

Conclusions:

• 14-day HDBR significantly alters vascular reactivity to both vasodilatory and vasoconstrictor stimuli.
• Bed rest appears to change the regulation of vascular dilation and the balance between dilatory and constrictor influences.
• These findings highlight the impact of simulated microgravity on cardiovascular regulation.