Fluid shifts in weightlessness.

Area of Science:

• Space physiology
• Human adaptation to microgravity

Background:

• Leg volume and mass changes are critical indicators of fluid shifts during spaceflight.
• Previous studies suggest microgravity affects fluid distribution, but detailed inflight and postflight data are needed.

Purpose of the Study:

• To quantify leg volume and mass changes in astronauts during and after space missions.
• To compare these changes between different spaceflight missions (Skylab 4 and Shuttle).
• To assess the rate and magnitude of inflight and recovery fluid shifts.

Main Methods:

• Utilized multiple girth measurements to assess leg volumes.
• Conducted serial mass measurements during and after spaceflight.
• Analyzed data from Skylab 4 and Shuttle missions.

Main Results:

• Skylab 4: Leg volume reduced by 1.9 L (12.8%), with 1.1 L from the non-dominant leg. Postflight recovery was 65% complete within 1.5 hours.
• Shuttle: Dominant leg lost 0.9 L, with 90% recovery within 150 minutes. Postflight increases were 87% complete at 1.5 hours postlanding.
• Mass loss of 2.5 kg inflight (first 4 days) and gain of 2.7 kg during recovery (first 4 days) were observed on Skylab 4.

Conclusions:

• Spaceflight induces substantial leg volume and mass changes, primarily due to fluid shifts driven by altered hydrostatic pressures.
• These fluid shifts are more pronounced than those observed during bed rest.
• The rate and magnitude of these inflight and postflight changes have significant operational implications for astronaut health and mission planning.