Simultaneous determination of muscle 31P and O2 uptake kinetics during whole body NMR spectroscopy

Our understanding of O-2 uptake ((V) over dot o(2)) control mechanisms during exercise may be improved by the simultaneous determination of the kinetics of intramuscular high-energy phosphate turnover and pulmonary (V) over dot o(2). We therefore developed a technique for remote gas-exchange analysis while subjects exercised in a whole body 1.5-T NMR system. Knee-extension exercise was performed against restraining rubber bands in the prone position. Free induction decays were acquired every 1,875 ms by using a transmit-receive coil, which was placed under the quadriceps. This allowed P-31 spectra of intramuscular ATP, P-i, and creatine phosphate dynamics to be determined every 15 s. Airflow was measured with a custom-designed turbine and a 45-ft.-long cable to reach the volume-measuring module. This was located in an adjacent radio-frequency-shielded room, as was the respiratory mass spectrometer, which also used a 45-ft.-long sampling line. The respired gas profiles were not discernibly different from those that used the standard inlet; the increase in the delay was readily incorporated into the breath-by-breath algorithm, allowing the (V) over dot o(2) kinetics to be determined in concert with those of intramuscular phosphate metabolism.