Effect of Transcutaneous Vagal Stimulation (TVS) on Endothelial Function and Arterial Stiffness in Peripheral Artery Disease

Peripheral arterial disease (PAD) constitutes a major public health burden. The incidence of PAD increases with age and is associated with other comorbid cardiovascular disorders. Atherosclerosis which underlies PAD is associated with increased arterial stiffness and an enhanced inflammatory state as evidenced by increased levels of pro-inflammatory cytokines and markers. One the earliest signs of cardiovascular disease is endothelial dysfunction which is characterized by a decreased vasodilatory capacity of the vascular endothelium and this lesion predates the development of clinical atherosclerosis. Endothelial dysfunction has been shown to be widely prevalent in PAD. It is postulated that endothelial dysfunction is due to enhanced sympathetic drive, diminished parasympathetic drive, chronic inflammatory state all of which leads to reduced nitric oxide synthase activity in the vascular endothelium with subsequent loss of vasodilatory capacity. Studies have shown endothelial dysfunction to be reversible with pharmaco-therapeutic interventions, though these interventions are associated with their own adverse effects. Stimulation of Vagal nerve increases the parasympathetic activity while suppressing sympathetic drive, decreases inflammation and enhancing nitric oxide synthase activity. Recent experimental and clinical data suggest that low-level tragus nerve stimulation (by stimulating the auricular branch of the vagus nerve located at the tragus of the external ear) may produce the same desired neuromodulator effect compared to vagus nerve stimulation. It is however unknown if Transcutaneous Vagal Stimulation (TVS) would lead to improved endothelial function as measured by flow mediated dilatation (FMD) and laser speckle contrast imaging(LSCI), a non-invasive method of measuring endothelial function or decrease in arterial stiffness as measured by Pulse Wave Analysis (PWA), in patients with PAD. The objective of this study is to determine the impact of TVS on endothelial dysfunction as measured by FMD & LSCI and arterial stiffness. Study population will include patients with established diagnosis of PAD. After performing baseline FMD, LSCI and PWA patients will be randomized to TVS and sham stimulation with cross over. The patient randomized to TVS stimulation will obtain stimulation for 1 hour followed by measurement of FMD,LSCI and PWA. There will be a washout period of at least 24 hours with patient crossing over to the other arms thus serving as their self-control.