Orthostatic Intolerance After ISS and Space Shuttle Missions

Area of Science:

• Space medicine
• Cardiovascular physiology
• Human adaptation to microgravity

Background:

• Cardiovascular deconditioning is a known consequence of spaceflight, increasing the risk of orthostatic intolerance.
• Orthostatic intolerance is more prevalent after longer missions, necessitating research into recovery timelines.

Purpose of the Study:

• To compare the incidence of orthostatic intolerance and recovery rates between astronauts from International Space Station (ISS) and Space Shuttle missions.
• To determine if flight duration influences the ability to complete an orthostatic tilt test (OTT) post-flight.

Main Methods:

• 20 ISS and 65 Shuttle astronauts underwent 10-min 80° head-up tilt tests before launch, on landing day (R+0), and 3 days post-landing (R+3).
• Statistical analyses included Fisher's Exact Test, Cox regression, and mixed model analysis to compare OTT completion and cardiovascular parameter recovery between groups.

Main Results:

• A significantly lower proportion of ISS astronauts completed the OTT on R+0 (2/6) compared to Shuttle astronauts (52/65).
• By R+3, most astronauts from both groups completed the OTT, but recovery was slower in ISS astronauts.
• Stroke volume and diastolic blood pressure predicted OTT completion and showed similar alterations but slower recovery in ISS astronauts.

Conclusions:

• ISS astronauts exhibit a greater incidence of orthostatic intolerance and slower recovery post-mission compared to Space Shuttle astronauts.
• Mission planners and medical teams must account for extended recovery periods for astronauts after long-duration spaceflights.
• Tailored post-flight activities and medical support are crucial for managing protracted recovery from microgravity exposure.