Patients with chronic heart failure (CHF) exhibit dysfunction of the vascular endothelium. This has been demonstrated as reduced reactive hyperaemic vasodilatation in a limb following release of a proximal occlusion and by impaired flow-mediated ultrasound-detected dilatation of conduit arteries, e.g. brachial, radial, following release of either proximal or distal occlusions. We have shown that distal occlusion (DO) in combination with venous occlusion plethysmography can detect enhanced flow-mediated dilatation in human limbs after a single bout of whole body exercise or local muscle activity induced by electrical stimulation in young healthy subjects (Rosbergen et al. 2000). In this study, this method was used to assess the effects of chronic low-frequency electrical stimulation on limb vasodilatation in CHF patients and age-matched control subjects.

With approval from the South Birmingham Local Research Ethics Committee, eight CHF patients aged 62 ± 11 years (mean ± S.D.), ejection fraction 32 ± 6 %, and 10 age-matched (65 ± 7 years) healthy subjects were recruited. Calf blood flow was measured by venous occlusion plethysmography (Filtrass 2000, DOMED) immediately on release of an ankle cuff inflated to suprasystolic pressure for 10 min, and at 20 s intervals thereafter until return to baseline. Measurements were made before and after a 4 week period during which all participants used electrical muscle stimulators (NT 2000, NeuroTech) to activate calf muscles for 3 X 20 min per day, at a frequency of 8 Hz, pulse duration 250 µs, maximum tolerable intensity.

Prior to stimulation, peak blood flows on release of DO were ~30 % lower in CHF patients than in age-matched controls (3.38 ± 0.32 vs. 4.86 ± 0.33 ml min^-1 100 ml^-1, P < 0.05, Mann-Whitney), and both were lower than those reported for young healthy subjects (Rosbergen et al. 2000). After chronic stimulation, peak blood flows on release of DO had increased significantly for both CHF and age-matched groups (4.77 ± 0.46 and 6.42 ± 0.59 ml min^-1 100 ml^-1, respectively, both P < 0.05 vs. pre-stimulation values, Wilcoxon signed ranks). Thus plethysmography after DO can detect both impairment of flow-mediated dilatation in CHF patients and in ageing, and the positive effects of stimulation therapy. Chronic electrical stimulation offers an alternative means of improving limb vascular function in a targeted fashion that avoids the central cardiovascular limitations of whole body exercise.

This work was supported by the British Heart Foundation. BMR NeuroTech are thanked for assistance with stimulators.