Exercising calf muscle T2∗ changes correlate with pH, PCr recovery and maximum oxidative phosphorylation

• Published in: NMR in biomedicine Vol. 27; no. 5; pp. 553 - 560
• Main Authors: Schmid, Albrecht Ingo, Schewzow, Kiril, Fiedler, Georg Bernd, Goluch, Sigrun, Laistler, Elmar, Wolzt, Michael, Moser, Ewald, Meyerspeer, Martin
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.05.2014
• Subjects: 31P MRS; 7 Tesla; Adult; Demography; Echo-Planar Imaging; energy metabolism; exercise; Exercise - physiology; Female; Humans; Hydrogen-Ion Concentration; Leg - physiology; Magnetic Resonance Imaging; Male; Muscle, Skeletal - physiology; Oxidative Phosphorylation; Phosphocreatine - analogs & derivatives; Phosphocreatine - metabolism; plantar flexion; skeletal muscle; Time Factors; Young Adult; 31P MRS; plantar flexion; pH; exercise; skeletal muscle; T2; energy metabolism; 7 Tesla
• ISSN: 0952-3480; 1099-1492; 1099-1492
• DOI: 10.1002/nbm.3092

Skeletal muscle metabolism is impaired in disorders like diabetes mellitus or peripheral vascular disease. The skeletal muscle echo planar imaging (EPI) signal (SEPI) and its relation to energy metabolism are still debated. Localised 31P MRS and SEPI data from gastrocnemius medialis of 19 healthy subjects were combined in one scanning session to study direct relationships between phosphocreatine (PCr), pH kinetics and parameters of T2∗ time courses. Dynamic spectroscopy (semi‐LASER) and EPI were performed immediately before, during and after 5 min of plantar flexions. Data were acquired in a 7 T MR scanner equipped with a custom‐built ergometer and a dedicated 31P/1H radio frequency (RF) coil array. Using a form‐fitted multi‐channel 31P/1H coil array resulted in high signal‐to‐noise ratio (SNR). PCr and pH in the gastrocnemius medialis muscle were quantified from each 31P spectrum, acquired every 6 s. During exercise, SEPI(t) was found to be a linear function of tissue pH(t) (cross‐correlation r = –0.85 ± 0.07). Strong Pearson's correlations were observed between post exercise time‐to‐peak (TTP) of SEPI and (a) the time constant of PCr recovery τPCr recovery (r = 0.89, p < 10− 6), (b) maximum oxidative phosphorylation using the linear model, Qmax, lin (r = 0.65, p = 0.002), the adenosine‐diphosphate‐driven model, Qmax,ADP (r = 0.73, p = 0.0002) and (c) end exercise pH (r = 0.60, p = 0.005). Based on combined accurately localised 31P MRS and T2∗ weighted MRI, both with high temporal resolution, strong correlations of the skeletal muscle SEPI during exercise and tissue pH time courses and of post exercise SEPI and parameters of energy metabolism were observed. In conclusion, a tight coupling between skeletal muscle metabolic activity and tissue T2∗ signal weighting, probably induced by osmotically driven water shift, exists and can be measured non‐invasively, using NMR at 7 T. © 2014 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd. During exercise, the skeletal muscle EPI signal time course (SEPI(t)) was found to be a linear function of tissue pH(t), and PCr recovery rates and maximum oxidative phosphorylation correlated with post exercise time to peak of the T*2 weighted signal. Data of 19 volunteers were acquired at 7 T, using a form‐fitted 31P/1H coil array. Dynamic localised 31P spectroscopy and 1H EPI with 6 s repetition time were acquired consecutively in one session before, during and after 5 min of plantar exions.