Phosphocreatine kinetics in the calf muscle of patients with bilateral symptomatic peripheral arterial disease during exhaustive incremental exercise

Purpose: To investigate the relationship between the atherosclerotic lesion load determined on magnetic resonance angiography (MRA) and phosphocreatine (PCr) kinetics during incremental, exhaustive calf exercise in patients with bilateral, symptomatic peripheral arterial disease (PAD). Procedures: Using a 1.5 Tesla MR scanner, 26 patients with bilateral symptomatic PAD and 24 healthy male controls underwent serial phosphorus-31 MR spectroscopy (31P MRS) during incremental exercise at 2, 3, 4, and 5 Watts. For each increment and recovery, PCr time constants, amplitudes of PCr changes and pH values were calculated from the MR spectra. In patients, the run-off resistance (ROR) was determined on MRA. Results: The patients exhibited significantly (C <= 0.002) increased PCr time constants at the first (36.7, 13.8-360.3 vs. 22.9, 9.2-60.7 s), at the second (68.1, 4.2-757.2 vs. 18.3, 5.2-57.6 s), at the third (65.3, 14.7-277.7 vs. 29.0, 4.48-97.2 s), the fourth increment (64.1, 34.2-548.8 vs. 34.6, 4.9-106.2 s), and during recovery (53.2, 11.1-353.2 vs. 41.4, 15.1-122.4 s) compared to the normal controls. The PCr on-kinetics during the increments correlated significantly with the pH levels (r=-0.39 to -0.66, p <= 0.005) at the end of the corresponding increments, but not with the RORs. Conclusions: The correlation between PCr on-kinetics and end-increment pH values might indicate remodelling processes within the muscle that probably affect mitochondrial performance, diffusion of oxygen, and muscle fiber distribution. These parameters could be improved by exercise training.