The influence of muscle contraction on the degree of microvascular perfusion in rat skeletal muscle following transcutaneous neuromuscular electrical stimulation

Electrotherapy is used clinically according to a variety of protocols and at various intensities with the intent of effecting any number of physiological changes. The purpose of this study was to determine if the increased degree of microvascular perfusion observed following 2,500 Hz transcutaneous neuromuscular electrical stimulation (TNMES) is dependent on evoked muscle contractions. The tibialis anterior (TA) and extensor digitorum longus (EDL) muscles from 30 male rats were analyzed. Six animals were untreated and served as controls, while the TA and EDL muscles of six animals were treated with TNMES at current intensities three times that needed to evoke a minimum visible contraction in the TA (M-TNMES). The remaining animals were treated with gallamine, which effectively blocked neurally mediated muscle contraction. The TA and EDL muscles of six gallamine-treated rats received no TNMES and served as shams (G-Sham), six received M-TNMES (GM-TNMES), and six received TNMES at intensities sufficient to produce sustained muscle contraction with a neuromuscular blockade in place (G-HIS). Perfused microvessels were labeled with fluorescein isothiocyanate-bovine serum albumin. The degree of microvascular perfusion was determined by calculating perfused microvessel/muscle fiber ratios (PV/F). The mean PV/F ratios of all groups were compared using Fisher's LSD (α = 0.05). When compared to controls, the PV/F ratios of the TA and EDL muscles in M-TNMES and G-HIS groups showed a significant (p ≤ 0.05) increase while the G-Sham and GM-TNMES groups were similar to controls. These results suggest that the increased degree of microvascular perfusion in stimulated skeletal muscle subsequent to 2,500 Hz TNMES is dependent on evoked muscle contractions. If experimentally evoked responses in animal models can be used as indicators of similar responses in humans, these results suggest that 2,500 Hz TNMES should be applied at intensities sufficient to produce a muscle contraction in order to increase the degree of microvascular perfusion in the stimulated skeletal muscle.