The effects of transcutaneous electroacupuncture stimulation (TEAS) on heart rate variability (HRV) and nonlinearity (HRNL): Is stimulation frequency or amplitude more important?
Creators: name: Mayor, David
name: Steffert, Tony
name: Panday, Deepak
Publisher: name: F1000 Research Limited
Year: 2019

description: Background. Heart rate variability (HRV) is increasingly used in acupuncture research as a measure of parasympathetic/sympathetic (PNS/SNS) balance. Heart rate nonlinearity (HRNL) is a new ‘PNS-like’ measure that also reflects this balance. Our aim here was to investigate if frequency or amplitude of transcutaneous electroacupuncture stimulation (TEAS) has greater effects on HRV/HRNL. To our knowledge, this is the only study published to date that investigates our research question.<br><br>Methods. In this single-blind, semi-randomised cross-over study, ethics approval was obtained and 66 participants attended for four sessions each. Following an initial 5-minute baseline recording, TEAS was applied for 20 minutes to each hand between acupuncture point LI4 <i>(hegu</i>) and the ulnar border. In each session, stimulation was at a different frequency – 2.5, 10 or 80 pps (pulses per second) at a ‘strong but comfortable’ amplitude, or as ‘sham’ at 160 pps and zero amplitude. After stimulation, recording was continued for 15 minutes to assess post-stimulation changes (making eight 5-minute recordings for each session). ECG (electrocardiograph) data was collected using a Mitsar-EEG-202 amplifier and down-sampled to 500 Hz. After pre-processing in Matlab and Kubios HRV software, 1988 clean 5-minute recordings  were available for analysis in Excel and SPSS using nonparametric methods.  Fifty-six different HRV and five HRNL measures were considered as indices of PNS or SNS function and subgroups of measures then selected for further examination as described in the Background information provided online.<br><br>Some results. On the basis of ECG-derived HRV measures and HRNL indices, TEAS at 10 pps appeared in this study to be experienced as less stressful than at 2.5 or 80 pps. Higher amplitude TEAS was in general experienced as more stressful, and the amplitude high-low differential had most effect at 10 pps. In general, stimulation at high and low amplitudes had opposite effects when comparing active stimulation at all frequencies with sham. Moreover, when 10 pps and 2.5 pps were compared with sham stimulation, greater numbers of significant differences were present <i>after</i> than <i>during</i> stimulation, with beneficial changes evident particularly after 10 pps TEAS. Most (and greatest) differences from sham were found for 10 pps TEAS at low amplitude (particularly for PNS-like measures and indices).<br><br>Findings with potentially useful clinical applications are that: (1) At all frequencies, <i>strong TEAS may be experienced as stressful</i>; (2) <i>TEAS at 10 pps is more likely to decrease the stress response than at 2.5 or 80 pps</i>, particularly following stimulation.  <i> </i><br><br>Proviso. However, further analysis is required to clarify questions raised by the current study, including (1) the effects of baseline values of HRV and mood measures, (2) the relevance of participant preference for stimulation at particular frequencies, (3) the usefulness of pulse rate variability (PRV) in addition to HRV, and (4) the benefits of using more refined HRNL measures.