Atrophy of calf muscles by unloading results in an increase of tissue sodium concentration and fat fraction decrease: a Na-23 MRI physiology study

作者：Gerlach D A^*; Schopen K; Linz P; Johannes B; Titze J; Zange J; Rittweger J

来源：European Journal of Applied Physiology, 2017, 117(8): 1585-1595.

DOI：10.1007/s00421-017-3647-4

• Sodium
• MRI
• Na-23 MRI
• Tissue sodium concentration (TSC)
• Quantification
• Muscle unloading

Purpose Na-23 MRI demonstrated increased tissue sodium concentrations in a number of pathologies. Acute atrophy results in muscle fibre volume shrinking that may result in a relative increase of extracellular volume and might affect sodium concentration. Thus, we hypothesized that local unloading of the calf muscles would lead to a decrease in muscle volume and an increase in muscle tissue sodium concentration.
Method One lower leg of 12 healthy male subjects was submitted to a 60 day long period of unloading using the Hephaistos orthosis, while the other leg served as control. Na-23 MRI and 2D PD-weighted Dixon turbo spin echo were obtained from the control and orthosis leg using a 3T scanner. For quantification, a sodium reference phantom was used with 10, 20, 30, and 40 mmol/L NaCl solution.
Result Tissue sodium concentration (TSC) increased as an effect of unloading in the orthosis leg. Relative increases were 17.4 +/- 16.8% (P = 0.005) in gastrocnemius medialis muscle, 11.1 +/- 12.5 (P = 0.037) in gastrocnemius lateralis muscle, 16.2 +/- 4.7% (P < 0.001) in soleus muscle, 10.0 +/- 10.5% (P = 0.009) in the ventral muscle group, and 10.7 +/- 10.0% (P = 0.003) in the central muscle group, respectively. TSC in the control leg did not significantly change. In the orthosis leg, muscle volume decreased as follows: medial gastrocnemius muscle: -5.4 +/- 8.3% (P = 0.043) and soleus muscle: -7.8 +/- 15.0% (P = 0.043).
Conclusion Unloading atrophy is associated with an increase in muscle sodium concentration. Na-23 MRI is capable of detecting these rather small changes.

• 出版日期2017-8