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

Objectives: Spaceflight back pain and intervertebral disc (IVD) herniations cause problems in astronauts. Purpose of this study was to assess changes in T2-relaxation-time through MRI measurements before and after head-down tilt bed-rest, a spaceflight analog. Methods: 8 men participated in the bed-rest study. Subjects remained in 6 degrees head down tilt bed-rest in two campaigns of 21 days, and received a nutritional intervention (potassium bicarbonate 90 mmol/d) in a cross-over design. MRI measurements were performed 2 days before bed-rest, as well as one and five days after getting up. Image segmentation and data analysis were conducted for the IVDs Th12/L1 to L5/S1. Results: 7 subjects, average age of 27.6 (SD 3.3) years, completed the study. Results showed a significant increase in T2-time in all IVDs (p < 0.001), more pronounced in the nucleus pulposus than in the annulus fibrosus (p< 0.001). Oral potassium bicarbonate did not show an effect (p=0.443). Pfirrmann-grade correlated with the T2-time (p< 0.001). Conclusions: 6 degrees head-down tilt bed-rest leads to a T2-time increase in lumbar IVDs. Oral potassium bicarbonate supplementation does not have an effect on IVD T2-time.