Shoulder transcutaneous electric nerve stimulation decreases heart rate via potentiating vagal tone

Abstract

By enhancing vagal activity, auricle transcutaneous electric nerve stimulation (TENS) is developed as a non-invasive therapy for heart failure. Nevertheless, though shoulder TENS used for treating adhesive capsulitis could affect vagal tone, its potential impact on heart functions remains unclear. In this study, electrocardiogram (ECG) and heart rate (HR) of subjects in response to sham, right-sided, or left-sided shoulder TENS (TENS-S, TENS-R, and TENS-L, respectively; 5 min) were recorded and analyzed. During the stimulation period, TENS-R constantly and TENS-L transiently decreased the HR of subjects; both TENS-R and TENS-L increased powers of the low- and high-frequency spectra. While TENS-R exhibiting no effect, TENS-L increased the ratio of low/high-frequency power spectrum indicating TENS-R decreased the HR through potentiating cardiac vagal tone. Collectively, these results suggest TENS could be an early and non-invasive therapy for heart failure patients before considering implant devices or devices are not feasible; moreover, therapists/physicians need to carefully monitor the potential adverse events during treatment for patient safety.Trial registration: The study protocol was registered in ClinicalTrials.gov (NCT03982472; 11/06/2019).

Conflict of interest statement

The authors declare no competing interests.

© 2021. The Author(s).

Figures

Figure 1

(A) The flow chart of participant recruitment and data analysis. Initially, 24 subjects were assigned to receive either the sham stimulation (TENS-S) or TENS on the right shoulder (TENS-R). After the preliminary analysis, 9 additional subjects were recruited and tested with TENS on the left shoulder (TENS-L). Data obtained from all experiments were then collectively analyzed. (B) The waveform of TENS. The upper trace is the waveform of TENS used in the current study. Waveform marked by the dash lines is amplified as the middle traces. Bottom left: each spike is a triple pulse with 1 ms pulse duration and each separated by a 1 ms interval. Bottom right: the frequency maintained at 200 Hz in the late period of stimulation. (C) The location of electrodes of TENS. Black blocks indicate the location of electrodes in TNES-S and TENS-R; red blocks indicate that in TENS-L. Stimulating electrodes ( −) were placed in the front of the should at the level of the suprasternal notch at about 2 finger-width medial and lateral from the mid-clavicle line; dispersive electrodes ( +) were placed at the back of the shoulder opposite to the stimulating electrodes. (D) The follow chart of TENS application. Before the stimulation, there was an equilibrium period of 10 min and then the recording started for 20 min. TENS was turned on after a 5 min baseline recording and lasted for 5 min. The recording stopped at 10 min after TENS offset.

Figure 2

Electrocardiogram (ECG) and heart rate (HR) of subjects in response to (A) sham stimulation (TENS-S) and (B, C) TENS on the right and left shoulder (TENS-R and TENS-L, respectively) for 5 min. The black bar at the bottom indicates the stimulation period.

Figure 3

Mean heart rate (HR) of subjects in response to (A) sham stimulation (TENS-S) and (B, C) TENS on the right and left shoulder (TENS-R and TENS-L, respectively). The black bar at the bottom indicates the stimulation period. DF = 2, F = 5.31; p < 0.01 among groups; DF = 9, F = 1.94; p < 0.05 among time points; Two-way ANOVA. *p < 0.05; **p < 0.01 versus baseline control; post hoc.

Figure 4

Individual heart rate (HR) of subjects at baseline control (CONT) and 3 min following (A) sham stimulation (TENS-S 3’) and (B, C) TENS at the right and left shoulder (TENS-R 3’ and TENS-L 3’, respectively). Mean HR of CONT and TENS-S/R/L 3’: (A) 77.30 ± 2.31 and 77.00 ± 1.98, (B) 73.84 ± 1.55 and 72.23 ± 1.49, and (C) 76.44 ± 2.18 and 74.77 ± 1.95 bpm, respectively.

Figure 5

Spectrum analysis of heart rate variability. (A, B) Power of the low-frequency (LF) and high-frequency spectra as well as (C) Power ratio of LF to HF spectrum (LF/HF) at baseline control (CONT) and during the period of sham stimulation (TENS-S) and TENS on the right and left shoulder (TENS-R and TENS-L, respectively). (A–C) all DF = 2, F = 3.48, 3.30, and 3.19, respectively; all p < 0.05 among groups; all DF = 1, F = 21.63, 21.04, and 15.40, respectively; all p < 0.01 between treatment; Two-way ANOVA. *p < 0.05 versus baseline control; post hoc.