The efficacy of transcutaneous electrical nerve stimulation on the improvement of walking distance in patients with peripheral arterial disease with intermittent claudication: study protocol for a randomised controlled trial: the TENS-PAD study

Validating the efficacy of TENS as an adjuvant technique for physical exercise is an important opportunity to improve walking capacity in patients with vascular claudication.

It is well known that PAD patients have low-level physical activity; only 3500 to 4500 steps per day on average, which is far below World Health Organisation recommendations (10,000 steps per day) [27‐30]. It is interesting to note that TENS has been already studied in healthy subjects. Several studies have reported that low-frequency TENS improves the perfusion of the superficial tissues, measured by enhanced laser Doppler imaging, by up to 40% [31‐33]. In a PAD patient, one very recent case study reported encouraging results on the improvement in ABI after using this technique [34]. The protocol used was as follows: 45 min per session, twice a day, for 3 months. The ABI of the affected leg increased from 0.63 to 0.71 after 3 months (then to 0.80 1 month later at a follow-up consultation), while the ABI in the leg without TENS did not change. The authors concluded that prospective, randomised controlled studies are necessary to better understand the effects of low-frequency TENS on the improvement in muscle perfusion in PAD patients.

Our team studied the effects on TENS on muscle sympathetic nerve activity (MSNA) in chronic heart failure (CHF) [35]. According to the results of our study, both TENS and neuromuscular electrostimulation (NMES) are able to reduce MSNA compare to sham stimulation (63.5 ± 3.5 versus 69.7 ± 3.1 bursts/min, p < 0.01 after TENS and 51.6 ± 3.3 versus 56.7 ± 3.3 bursts/min, p < 0.01 after NMES), suggesting that TENS to the lower limbs could inhibit sympathetic outflow directed to the legs in CHF patients and could be able to reduce vasoconstriction. In PAD, oxidative stress and reduced blood flow to working muscles induce the augmented blood pressure response to exercise caused by an exaggerated exercise pressor reflex (PR) [36‐38]. The PR is a neurological reflex that increases sympathetic nervous system activity, constricts arterioles and increases blood pressure. It is well known that TENS treatment releases endogenous opioids in the central nervous system and produces analgesia [39‐41]. Furthermore, it has been shown in previous animal studies that the stimulation of opioid receptors of group-III and -IV afferent endings contributes to attenuating the exaggerated exercise PR observed in rats with ligated femoral arteries [38, 42, 43]. Thus, according to our hypothesis, TENS could be a new technique to reduce sympathetic nerve activity, the PR, and to induce a neuromodulation of the vascular tonus in PAD in addition to its traditional direct analgesic effects. This easy-to-use therapeutic tool could prove to be extremely interesting as it is easy to transport for use at home so that patients can use it to complement daily walking exercise. In the long term this could be useful in discouraging a sedentary lifestyle and will hopefully guarantee a higher level of physical activity and thus have an impact on secondary prevention after PAD.