Acute Muscle Damage Is Augmented After Exercise In PAD Patients: Evidence From Diffusion Tensor Imaging

Abstract

Although the chronic myopathies associated with peripheral arterial disease (PAD) are well established, the acute muscular responses to exercise in this population are less clear. PURPOSE: This study used diffusion tensor imaging (DTI) to compare acute exercise related muscle damage between PAD patients and healthy controls. METHODS: Eight PAD patients and 7 healthy controls performed graded dynamic plantar flexion exercise in the bore of a 3T MRI scanner. In order to compare responses between the active and inactive legs, these plantar flexion trials were repeated during imaging of the exercising leg and imaging of the resting leg. Each exercise trial began at 2kg, and increased by 2kg every 2 minutes until fatigue, or until completion of 10kg. DTI images were collected from the widest portion of the calf pre and post exercise, and were analyzed for mean diffusivity (MD), fractional anisotropy (FA), and eigenvectors 1-3 (λ1-3) of the medial gastrocnemius (MG) and tibialis anterior (TA) muscles. RESULTS: At baseline, there were no significant group differences in MD, FA, or any of the individual eigenvectors for the MG or TA of the exercising leg (P>0.34). However, results did indicate significantly greater increases in MD (+13.6 ± 10.6% and +2.5 ± 3.5%), λ1 (+13.7 ± 14.3% and +1.4 ± 3.1%), λ2 (+13.8 ± 10.5% and +3.0 ± 3.6%), and λ3 (+13.1 ± 7.1% and +3.7 ± 4.3%, all P<0.02) in the MG of the exercising leg in PAD patients compared to controls, respectively. Results also indicated a significantly greater increase in λ3 of the TA in the exercising leg in PAD patients compared to controls (2.1 ± 2.9% and -1.5 ± 1.4, respectively, P=0.01). In contrast, no significant group by time interactions were observed in the resting leg (all P>0.15). CONCLUSIONS: These data indicate that skeletal muscle diffusivity increases more in PAD patients compared to controls after exercise. Ultimately, this suggests that acute exercise related muscle damage is augmented in PAD patients. Supported by NIH P01-HL134609 (Sinoway) and UL1 TR002014 (Sinoway).