Functional electrical stimulation effect on skeletal muscle blood flow measured with H 215O positron emission tomography

Abstract

Objective: To test the hypothesis that the limitation in muscle power development with functional electrical stimulation (FES) results from an insufficient increase in muscle blood flow (MBF) in response to activity. Subjects and Methods: Five subjects with neurologically complete spinal cord injury (SCI) were tested to measure the MBF response to FES-induced knee extension. The MBF response to voluntary knee extension was measured in five age-matched, able-bodied controls. MBF was measured with positron emission tomography (PET) using H 2 15O as a tracer. Three scans were performed with muscle at rest (baseline), immediately after 16min of FES-induced or voluntary knee extension (activity), and 20min after the second scan (recovery). Results: In SCI subjects, mean ± SE MBF (mL/100g/min) values were: baseline = 1.85 ± .48; post-FES = 31.9 ± 5.65 ( p = .0058 vs baseline); recovery = 6.06 ± 1.52 ( p = .0027 vs baseline). In able-bodied controls, mean ± SE MBF values were: baseline = 8.52 ± 3.24, post-voluntary exercise = 12.62 ± 3.03 ( p = .023 vs post-FES in SCI subjects); recovery = 10.7 ± 6.01. Conclusions: MBF does not appear to be the limiting factor in muscle power generation with FES. The greater increase in MBF observed with FES in SCI subjects when compared with able-bodied subjects performing a similar task (unloaded knee extension against gravity) may relate to abnormal metabolism in FES-stimulated muscle.