Floyd Settles, Presenter: Nothing to Disclose

Geoffrey D. Clarke PhD, Abstract Co-Author: Nothing to Disclose

Measurement of mitochondrial function  is relevant to aging, diabetes and sports medicine. Phosphorus-31 magnetic resonance spectroscopy (31P-MRS) can be used to evaluate the rate of phosphocreatine (PCr) recovery following exercise as a noninvasive index of the rate of ATP synthesis. The project’s aim is to develop a reproducible measurement technique using an exercise apparatus to quantify PCr recovery in the vastus lateralis muscle (VL).

The apparatus was designed to exercise the VL with subjects in supine position with a dual-tuned 1H-31P TX/RX surface coil strapped to the thigh. PCr depletion levels and recovery times were measured for 8 minutes following a 5 min period of exercise. Slice-selective 31P-MRS was performed on 5 subjects (4 male, 15-56 y.o.) with TR=3000 ms, NSA=2, BW=2200 Hz. The time for return of PCr values to their half-maximum (T-half) was used as an index for the rate of ATP synthesis. PCr recovery data were fit to the function PCr(t) = PCr(0)+D[1-exp(-bt)] using the Marquardt-Levenberg algorithm (nlsLM function) in the R statistical package, where D and b were the fitted variables.

The prototyped apparatus is a compact, single-piece PVC assembly with little mass (<3 kg) for ease of installation. The device is adjustable to fit a range subjects from 58” to 78” tall and provides resistance of up to 13.5 kg within the confines of the magnet bore. Subject setup time is a five minutes. Resistive force is adjustable to a subject’s physical ability so a level of muscle fatigue and PCr depletion occurs within the five minute exercise window. Subjects reported that the apparatus is stable and comfortable. Exercise produced a rapid drop in PCr and concomitant increase in inorganic phosphate (Pi) in all subjects. The average PCr recovery T-half = 36.3 s ± 7.8 s for the five subjects.

The exercise apparatus works, supporting and immobilizing the thigh and surface coil during baseline, dynamic flexion exercise and recovery phases of the protocol. Spectral data acquired consistently demonstrated  PCr depletion and recovey in VL across all subjects. Predictable extension of the lower leg is obtained with a constant resistance without the use of large weights.

Noninvasive, reproducible measures of mitochondrial function by a well-characterized in-vivo biomarker can provide insights for the characterization and treatment of metabolic diseases.

Settles, F, Clarke, G, Exercise System for Using 31-phosphorus MR Spectroscopy to Monitor Phosophocreatine Recovery from Exercise as Index for Mitochondrial Metabolism.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13020671.html