Correlation of MR changes with Doppler US measurements of blood flow in exercising normal muscle

Muscle data from phosphorus-31 magnetic resonance (MR) spectroscopy and hydrogen-1 MR imaging and popliteal artery data from duplex Doppler ultrasound were compared during an exercise test of the anterior compartment of the leg, in nine healthy volunteers. Significant variations (mean +/- standard deviation) were observed at the end of exercise versus rest in intracellular pH (pHi) (6.32 +/- 0.02 vs 7.02 +/- 0.04, P < .001), T2 (38.2 msec +/- 2.3 vs 29.5 msec +/- 1.1, P < .001), and popliteal output (652 mL/min +/- 232 vs 149 mL/min +/- 65, P < .001). These variables showed the following significant correlations at the end of exercise: T2 and pHi (r = -.784, P < .01), T2 and popliteal output (r = .737, P < .03), and pHi and popliteal output (r = -.902, P < .001). However, during recovery, the T2 curve was significantly different from those of pHi and popliteal output. This suggests that even if circulatory conditions play a role in the maximum T2 variation during exercise, they do not directly explain T2 changes. Furthermore, the correlations involving pHi suggest the role of the metabolism of exercising muscle in transcapillary fluid movement.