Numerous studies have examined disc volume, height, and disc fluid loss to more clearly understand the effects and rate of cellular diffusion and nutrient and waste transfer on IVD. However, to date, there have been no significant measurements of the rate at which discs lose fluids during normal activity throughout the day. We know that IVD fluids are replenished during overnight rest, but understanding how quickly the fluids dissipate during daily activity could be important in the prevention and treatment of disc degeneration.
To better understand the rate at which discs lose fluids after an overnight gain, researchers conducted a study 1 of five healthy subjects—four women, and one man— between the ages of 21 and 32 years old. Each of the subjects was screened prior to the beginning of the study to determine that they had no pathologies of the spine. The subjects were instructed to remain moderately active and resist sitting for more than 10 minutes at a time during the 10-hour period preceding the study.
On arrival in the evening, each of the subject was instructed to remain in an upright position for one hour, then they were placed into an MRI scanner for the first (PM) scan. The subjects then slept at the study facility and were instructed not to get out of bed except to use the bathroom. After 8 hours of sleep, they were scanned again at approximately 7am (AM).
All the subjects then began a regimen of 40 minute periods of walking, followed by horizontal MR scans. They repeated this protocol over an 8-hour period, until approximately 3pm.
Analysis of all 19 disc scans indicated an average gain of 10.6 % in disc volume overnight, as measured prior to activity in the morning. There was a clear and substantial decrease in this disc volume after the subjects walked during the day, but even after 8 hours of continuous walking (with breaks only for scans), the amount of volume (of fluid) remained higher than the volume that had been measured the previous night, prior to sleeping. This indicates the discs’ ability to retain fluids over an extended period throughout the day.
Researchers noted a large variance between the disc fluid loss of the study participants—from 11.1 % to -3.5 %. Because the volume is determined by the proteoglycan’s fluid-holding ability and by the seepage through the disc collagen, the enormous range in volume decrease between differing discs could be an indication that diverse types of disc and their fluid-retention (and nutrient and waste-dispensing) abilities could be more, or less susceptible to future degeneration. Future study is needed to determine which disc type is more beneficial and less likely to degenerate. Disc fluid loss and gains are important in understanding optimal metabolism.