T2-relaxation time increases in lumbar intervertebral discs after 21d head-down tilt bed-rest

Area of Science:

• Space medicine
• Biomedical imaging
• Spinal health

Background:

• Spaceflight poses risks to astronaut health, including back pain and intervertebral disc (IVD) issues.
• Head-down tilt bed rest is a common analog for studying spaceflight effects on the human body.
• MRI T2-relaxation time is a sensitive biomarker for assessing IVD hydration and degeneration.

Purpose of the Study:

• To evaluate changes in lumbar IVD T2-relaxation time following a 6° head-down tilt bed-rest period.
• To investigate the potential impact of potassium bicarbonate supplementation on IVD changes during bed rest.

Main Methods:

• Eight male participants underwent two 21-day campaigns of 6° head-down tilt bed rest in a crossover design.
• MRI scans were performed pre-bed rest and at 1 and 5 days post-bed rest.
• T2-relaxation times were analyzed in the intervertebral discs from Th12/L1 to L5/S1, with a focus on nucleus pulposus and annulus fibrosus.

Main Results:

• A significant increase in T2-relaxation time was observed across all lumbar IVDs (p<0.001).
• The increase in T2-time was more pronounced in the nucleus pulposus compared to the annulus fibrosus (p<0.001).
• Pfirrmann grade, a measure of disc degeneration, showed a significant correlation with T2-time (p<0.001).

Conclusions:

• 6° head-down tilt bed rest induces measurable changes in lumbar IVD T2-relaxation time, indicating altered disc hydration or composition.
• Oral potassium bicarbonate supplementation did not demonstrate a significant effect on IVD T2-relaxation time in this study.
• These findings highlight the impact of simulated microgravity on spinal structures and suggest potential areas for future countermeasures.