Simultaneous determination of muscle P-31 and O-2 uptake kinetics during whole body NMR spectroscopy

Our understanding of O-2 uptake ((V) over dot o(2)) control mechanisms duri ng exercise may be improved by the simultaneous determination of the kineti cs of intramuscular high-energy phosphate turnover and pulmonary (V) over d ot o(2). We therefore developed a technique for remote gas-exchange analysi s while subjects exercised in a whole body 1.5-T NMR system. Knee-extension exercise was performed against restraining rubber bands in the prone posit ion. 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 spe ctra of intramuscular ATP, P-i, and creatine phosphate dynamics to be deter mined 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 i n an adjacent radio-frequency-shielded room, as was the respiratory mass sp ectrometer, which also used a 45-ft.-long sampling line. The respired gas p rofiles were not discernibly different from those that used the standard in let; 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.