Novel Way To Increase Cardiac Vagal Activity By Applying Facial Skin Stimulation Using A Newly Developed Tool

Abstract

The application of cold stimulation to the facial skin is a simple test to assess trigeminal-vagal-cardiac function. However, cold stimulation induces unpleasant feeling and elevated systolic blood pressure. Recently, Hotta et al. (2012) observed that non-invasive, soft mechanical stimulation using a newly developed tool affects autonomic activity in rats. And if so, the facial skin stimulation by the tool appears to be increased in vagal activation in human. PURPOSE: To investigate the effect of non-invasive, soft mechanical stimulation to the facial skin using a newly developed tool on vagal activity. METHODS: Fourteen male college students were participated in this study. They were asked to lie supine at rest on an examination table for 6 min. During from 2nd to 4th min, soft mechanical (S), cold (C) stimulation, and non-simulation (N) were applied to the skin around lower jaw in a randomized order. Soft mechanical stimulation was applied by a tool which has small roller covered by elastomer resin (SOMAPLANE, Toyoresin, Japan) at a frequency of approximately 1 Hz. Cold stimulation was applied by a commercially available gel pack. Electrocardiogram (ECG) signals were recorded and heart rate variability (HRV) parameters were calculated by RR intervals (RRI) extracted from ECG. Blood pressure (BP) was measured at 1, 3, 5 min using an automated BP monitor system. After I and S conditions were complete, the subjects were asked to describe freely the perceived sensation of cold using numerical rating scale (NRS) to assess the intensity or discomfort on a subjective scale, in which 0 reflected no sensation and 10 were equivalent to unbearable discomfort. The delta values were expressed as the difference form baseline (0-2 min). RESULTS: Delta RRIs during stimulation (2-4 min) were significant increase in S (36.8±3.3 ms, P<0.0001) and C (36.5 ±51.8 ms, P=0.017) compared with baseline and post-stimulation (4-6 min), although no difference in N was observed. Delta HRV parameters and delta BP were no significant change throughout each trials among three conditions. There were significantly lower values in NRS on S compared with C (P=0.003, 1.4±1.4, 4.6±3.0, respectively). CONCLUSIONS: Non-invasive ‘soft’ stimulation to the facial skin using newly developed tool may increase parasympathetic activity at rest in human.