Microgravity-induced changes in aortic stiffness and their role in orthostatic intolerance

Area of Science:

• Cardiovascular physiology
• Space medicine
• Biomedical engineering

Background:

• Orthostatic intolerance (OI) is a common issue for astronauts after spaceflight.
• Cardiac output (CO) reduction during orthostatic stress is a key feature of OI.
• Arterial compliance (C(a)), particularly aortic compliance (C(ao)), influences venous return and CO.

Purpose of the Study:

• To test the hypothesis that microgravity-induced changes in C(a) protect against OI.
• To investigate the role of arterial and aortic compliance in microgravity-induced orthostatic intolerance.

Main Methods:

• Retrospective analysis of astronaut hemodynamic data post-spaceflight.
• Utilized a ground-based rat model simulating microgravity (hindlimb unloading).
• Measured in vivo pulse wave velocity (PWV) and in vitro pressure-diameter squared relationship (PDSR) of the thoracic aorta.

Main Results:

• Orthostatically tolerant (OT) astronauts showed decreased C(a) post-flight; OI astronauts showed increased C(a).
• Hindlimb-unweighted rats exhibited increased aortic stiffness (decreased C(ao)) compared to controls.
• Both human spaceflight and simulated microgravity induce changes in aortic compliance.

Conclusions:

• A microgravity-induced decrease in arterial compliance is a protective adaptation against orthostatic intolerance.
• Reduced C(a) lowers resistance to venous return, aiding CO maintenance during orthostatic stress in space.
• Understanding these vascular adaptations is crucial for mitigating OI in astronauts.