Transcutaneous electrical nerve stimulation at different frequencies on heart rate variability in healthy subjects

Sympathetic and parasympathetic nervous system imbalance has been strongly associated to sudden cardiac death. Among the non-pharmacological treatment, transcutaneous electrical nerve stimulation (TENS) represents a possible therapeutic intervention to reduce sympathetic excitation and improve the sympatho-vagal balance in different clinical conditions. We aimed to verify acute effects of high and low transcutaneous electrical nerve stimulation (TENS) frequencies by the evaluation of heart rate variability. Seven healthy volunteers received an application of low frequency (10-Hz) and high frequency (100-Hz) TENS. After 10-Hz, there was decrease of LF normalized units (n.u.) component (32.7 ± 5.9 vs 18.3 ± 3.4, p < 0.002) and increase of HF n.u. (60.9 ± 4.3 vs 72.6 ± 8.9, p < 0.016). In contrast, after 100-Hz there was increase of LF n.u. (31.5 ± 16.1 vs 41.6 ± 12.2, p < 0.019) and reduction of HF n.u. (63.9 ± 15.3 vs 53.7 ± 12.3, p < 0.031). In conclusion, TENS modulates sympathetic and parasympathetic activity in a frequency dependent manner.