Effect of Salivation by Facial Somatosensory Stimuli of Facial Massage and Vibrotactile Apparatus

2.1 The optimum way of hand massage

We performed facial stranger or personal hand stimuli during 3 and 5 min. After performing the stranger or self-massage procedures for 3 or 5 min, we asked for degree of fatigue. We included 40 healthy subjects (age 26.7 ± 2.4; 25 males, 15 females) and examined well-suited massage time and method depending on first 5 min and then 3 min massage. However, normal subjects were always appealed for feeling of fatigue with an exercise for 5 min. Hand massage for 3 min can be divided into stranger and self-massages: own face has been massaged by other person’ hand or by own hand. Personal massage is not able to treat patients with handicap and cerebral apoplexy. So, we focused at the exercise for 3 minutes and stranger massage (hand massage), as shown in Figure 1A.

After a stranger massage (a light touch and paratripsis massage) of the facial skin, we performed a rotation every second to increase the temperature of the skin and thus boost local blood circulation and improve the metabolism of the parotid glands and around the facial skin (Figure 1B).

We performed the resting and stimulating phases during insertion of cotton rolls for each 3 min between 5 and 7 pm under the circadian rhythm. We explored ECG (electrocardiogram), facial skin temperature, total salivations, OxyHb (oxidation hemoglobin) activity of f-NIRS (functional near-infrared spectroscopy) on the frontal cortex and amylase activity between resting and massage phase of the stranger hand massage. We recorded measurement of resting condition for 3 min after each cotton roll was set into the oral cavity, and then after relax of 1 min interval, new cotton roll was fitted into an oral cavity again and we did measurement of stimulating condition for 3 min. The facial skin temperature, RR intervals of ECG and f-NIRS recorded during experiments, and the observational study were measured in each measuring range. Furthermore, we recorded total salivation and saliva amylase activity after each phase of resting, hand massage, and vibrotactile stimulation.

2.2 The optimum frequency of vibrotactile apparatus

Apparatus of 89 Hz frequency and 9.8 μm amplitude vibrotactile stimulation was chosen by data of the previous papers [1, 5, 6, 7, 8], as shown in Figure 1B-a, -b. We tried three vibrotactile stimuli, (89, 114, and 180 Hz, and others all of 9.8 μm amplitude), and the best salivation was 89 Hz frequency in comparison with others, as shown in Figure 2. This apparatus was used by poor salivation patients (especially, Sjogrens’s syndrome and so on) and about 50% of patients showed the effect [1]. Stranger hand massage had a limit time to do massage for physical fatigue, so we tried the 89 Hz frequency vibrotactile apparatus for long time of facial stimulation. Furthermore, we recorded facial skin temperature, total salivation, RR intervals of ECG, and saliva amylase activity, too.

We explored the facial skin temperature, ECG recording, and fNIRS on the frontal cortex for the comparison with resting for 3 min, stranger massage for 3 min, and vibrotactile apparatus for 15 min.

2.3 Analysis of facial skin temperature

Facial skin temperature was measured by thermistor-pots (BioResarch Co.) located on the facial skin of parotid glands of both sides with adhesive tape, as shown in Figure 1C-a, -b. We recorded the temperature through the experiment and analyzed 3 min from start to finish during resting phase, 3 min from start to finish during stranger hand massage, and 15 min from start to finish during the vibrotactile stimulation.

2.4 Analysis of RR intervals of ECG

The electrocardiogram (ECG) recording was induced by the standard limb lead. The heart rate was measured by the RR interval rate (time between R and R) and was analyzed by the variance plot and frequency distribution, as shown in Figure 1C-a. On the other hand, in the distribution of frequency measured by RR interval rate, we decided a mean RR interval value in order to show almost monomodal peaks [9].

2.5 Analysis of total salivation

The mouths of each subject were fitted with rolls of cotton placed on both sides of the mouth at the following sites on the duct openings of the parotid glands of the buccal mucosa near the second upper molar teeth, and under the tongue to collect saliva from the sublingual and submandibular glands for a measurement of total salivation, as shown in Figure 1D. The total salivations indicate the sum of four cotton rolls (both sides of parotid, and submandibular and sublingual glands), as shown in Figure 1D. We measured the resting salivation for 3 min and after a relaxing interval of a minute, we did stranger hand massages salivation for 3 min again. Furthermore, we measured total salivations of the 15 min vibrotactile stimulation after 5 min resting interval of the massage.

2.6 Analysis of an OxyHb of fNIRS on the frontal cortex

The recording was conducted using a functional near-infrared spectroscopy (fNIRS) OEG16 instrument (SpectraTech, Inc., Shelton, CT, USA) from the frontal cortex. As shown in Figure 1C-a, -b, the fNIRS probe assembly consisted of six LEDs as light sources, each of which emitted two kind of wavelengths, 770 and 840 nm, and six photodiodes as detectors. The sources and detectors were symmetrically arranged in an area of 3.0–14.0 cm, with the nearest source-detector separation of 2.0 cm, and measurement points were at 16 points on a frontal cortex. During scanning, a velcro band held the probe assembly securely to the forehead of subjects and extended from ear to ear horizontally and from hairline to eyebrows vertically. Each of the LEDs was turned on in sequence, and the diffuse NIR light from each source was acquired through the cortical region at the nearest detector. Thus, 16 source-detector pairs (channels) in total were measured (Figure 1C-a, -b). The sampling rate across all 16 channels was 0.76 Hz. In particular, we showed a 16-channel computerized analysis (as shown in the previous papers [5, 6, 7]) and the original waves of four channel recording areas in the central parts. Analysis of amount of OxyHb of fNIRS on the frontal cortex is examined by the program of fNIRS Data Viewer, and we explored channels 4, 7, 10, and 13 of the central part of the frontal cortex. Data recorded by the experiment measured the value of integral of four channels in the center frontal cortex, and we calculated mean value of integral of four waves [5, 6, 10, 11].

2.7 Analysis of salivary amylase activity

A salivary amylase (α-amylase) activity was measured by salivary amylase monitor (Nipro Co.) provided for chips of salivary amylase monitor. Measurements of saliva amylase activities were recorded after resting, stranger hand massage, and vibrotactile stimulation phases.

3.1 Facial skin temperature

In 5 min hand massages, facial skin temperature increased about 2–3°C in both hand massages (stranger and personal). On the other hand, in 3 min stimuli, facial skin temperature increased about 1.5–2.0°C. The tendency of increased facial skin temperature in 3 and 5 min stimuli was almost same; namely, the ratio of increased temperature was dependent on stimulus time. On the other hand, in performance of stranger hand massages for 5 min, each operator complained with feeling of fatigue, and sometimes showed overflowing of salivation in the cotton rolls of the oral cavity. From this result, we abandoned this experiment of 5 min stimulation depending on using of five subjects. Furthermore, the 5 min massage procedure elicited the sure fatigue. So, we focused to 3 min stranger hand massage.

In loading, facial skin temperature showed about 33°C in the insert of cotton rolls in an oral cavity, as shown in Figure 3. This skin temperature may be stimulated by a foreign substance, because facial skin temperature was decreased up to about 32°C in the resting phase after loading. After a resting phase of 3 min stranger massage stage, facial skin temperature in the stranger massage increased from 32.0 to 34.5°C, as shown in Figure 3; namely, stranger massage showed the increase of facial skin temperature from 32.0 to 34.5 in 3 min stimulation.

On the other hand, the apparatus of 89 Hz frequency and 9.8 μm amplitude vibrotactile stimulation was chosen by data of the previous papers [1, 5, 6, 7, 8], as shown in Figure 1. This vibrotactile stimulation was the best salivation in comparison with others, as shown in Figure 2. In the resting phase, facial skin temperature showed about 32°C. Furthermore, the start of 89 Hz vibrotactile stimulation showed about 33°C and after 15 min, it did 34°C; namely, an increase of 1°C spent due to 15 min vibrotactile stimulation, as shown in Figure 3.

3.2 RR interval of ECG and total salivation

First, we examined the difference between stranger and self-massages of the RR intervals of ECG. However, there were no differences between the RR intervals of ECG of stranger and self-massages. Especially, the RR intervals in 3 min stranger massage had a tendency to decrease (increase of heart rate), and there was a p < 0.01 significance (T-test), as shown in Figure 4A. Namely, for 3 min of stranger massage, RR intervals increased from about 700 to 1000 ms, and it evoked feeling of sleepy in everybody, as shown in Figure 4A. However, a 89 Hz vibrotactile stimulation was spent for 15 min to increase from about 700 to 1000 ms of RR interval, as shown in Figure 4A. Especially, immediately after the insert of cotton rolls, RR intervals showed about 700 ms and then after a few min increased up to about 900–1000 ms, as shown in Figure 4A. In particular, hand massages are effective to increase temperature and RR intervals. However, no change of total salivation did not show the effect of the autonomic system in 3 min hand massage.

However, hand massages, especially stranger one, will evoke sleepiness by the increased temperature, and metabolism will decrease getting sleepy with the non-increased salivation. Especially, hand massage is needed to countermeasure the effectiveness of fight falling asleep.

On the other hand, total salivation showed about 1.2 ml in resting phase during 3 min, 0.5 ml in stranger massage during 3 min, 1.0 ml in self massage during 3 min, and 3.5 ml in 89 Hz vibrotactile stimulation during 15 min, as shown in Figure 4B. Although 3 min hand massages did not show the effect of autonomic activity, 15 min vibrotactile stimulation did it.

3.3 Measurement of OxyHb of fNIRS on the frontal cortex

The increase toward plus direction of OxyHb is associated with neuronal activities, but when we become sleepy, it is decreased toward below zero [12, 13]. On the other hand, the zero level of OxyHb of fNIRS showed parasympathetic activity from our data [5, 6, 7]. According to the amount of OxyHb of fNIRS, OxyHb in the stranger massage showed the decrease below zero, as shown in Figure 5. The results may be sleepy with decreased OxyHb during the stranger massage. According to analysis of OxyHb activity of fNIRS, during the resting phase and hand stimulation, subjects showed the nonzero number, and during the second half stimulation of 89 Hz vibrotactile apparatus, they showed the zero level. In particular, the below zero level of OxyHb activity coincided with the inducing of sleepy in the stranger massage. We think that the nonzero number is the decreased metabolism with getting sleepy, and the zero level is the parasympathetic activity (2–15 min in 89 Hz vibrotactile stimulation), as shown in Figure 5 and the previous papers [5, 6, 7, 8]; namely, the stranger massage will produce an early excitation (0–2 min) and a late relaxation (3 min), as shown in Figure 5.

3.4 Measurement of amylase activity

In the previous studies [10, 11, 14], measured values with salivary amylase monitor (Nipro Co.) showed the increased value depending on the sympathetic activity; namely, the value of amylase activity measured by salivary amylase monitor is shown as an increase of value following increased sympathetic activity. The results showed that the minimum value was before hand massage (about 15 KIU/L) and then the maximum value was after stranger massage (about 40 KIU/L) and vibrotactile apparatus (about 42 KIU/L), as shown in Figure 6. These findings show that subjects (patients) may be excited (decreased RR intervals, as shown in Figure 4A) by stranger’s hand touching (Figure 4B). Furthermore, it may be related to an amount of amylase.

4.1 Facial skin temperature

Firstly, although we tried to perform 5 min massage, there were three bad deficits: in 5 min massage, operators complained about being very tired and they cannot handle patients with handicaps and stroke. Furthermore, we performed by the measurement of salivation with the cotton roll method. When we measured the amount salivation of a cotton roll, subjects of 5 min stimulation with heavy salivation often leaked from a cotton roll [8]. So, we focused to 3 min stranger hand massage, and we measured facial skin temperatures after 3 min resting phase and after 3 min stranger hand stimulation phase. In 3 min stranger hand stimulation, facial skin temperature increased about 2.0°C, as shown in Figure 3. In particular, in comparison with before and after facial skin temperatures between resting and hand massage, although the resting phase increased as little as possible, the hand massage showed a big increase in temperature. On the other hand, a 89 Hz vibrotactile stimulation was spent for about 15 min to increase temperature (about 1.0°C), as shown in Figure 3. The finding showed that the stranger hand massage was especially effective in facial skin temperatures. As shown in Figure 3, a 89 Hz vibrotactile stimulation was spent for 15 min for an increase of 1°C [5, 6, 7, 8]. However, hand massages are adequate with 2–3 min for an increase of 1°C, as shown in Figure 3. Although a 89 Hz vibrotactile stimulation needs long time of 4–7 years as effective recovery, hand massage for 3 min may have more effect with a repetition of day after day, as shown in the previous paper [1]. A 89 Hz vibrotactile stimulation was spent for 15 min time for an increase of 1°C, and this apparatus got effective by using at morning and night. However, as hand massage was necessary for 1–2 min, we may get effect by doing at morning and night; namely, an effective increase in facial skin temperature may be elicited by a good metabolism for recovery [15].

4.2 Effect of autonomic activity

The effect of autonomic activity can directly be studied by changes in RR intervals of ECG and total salivation. The RR interval and salivation are controlled by an autonomic activation, and the increased RR intervals (decrease of heart rate) and a great deal of serous salivation are parasympathetic activity and the decreased ones (increase of heart rate) and a little mucus salivation are sympathetic activity [16, 17]. In the experimental room, the RR interval showed about 700 ms in the resting phase between 0 and 1, and after the resting phase of the latter half, it arrived in about 900 ms, as shown in Figure 4A. This insert of cotton rolls was activated by sympathetic nerve, and the RR intervals were decreased. Furthermore, in the resting phase of the latter half, it became naturalized, and the RR intervals increased, as shown in Figure 4A; namely, it showed the adaptation to the environment in latter resting phase. On the other hand, total salivation was decreased before and after hand massages, as shown in Figure 4B. This decrease may be activated by sympathetic nerve. Three minutes hand massages may be a small amount for the effective autonomic activity and an adequate massage times may produce an effective effort of the autonomic nerve. In the 3 min hand stimulation, they showed the increased rate in average values, and they showed significant differences (T-test, p < 0.01) in RR intervals. However, in total salivation, the hand massage may not show the effect of the autonomic nerves as 3 min stimulation. Although this finding may be an effective treatment, we thought inadequate recovery of a function for salivation. We reported the increased salivation depending on the 89 Hz vibrotactile stimulation on the facial skin [1, 5, 6, 7]. Namely, autonomic changes of stranger massage may be produced by an adequate stimulation time. However, the stranger hand massage did not show the total salivation, and always caused sleepiness after the experiments. We think increased temperature will show a good increased metabolism in stranger massage, but all of subjects are set to sue for sleepiness in the stranger massage. Namely, it is important to get not to sleep for prevention of a decline in metabolism.

4.3 Analysis of OxyHb of fNIRS on the frontal cortex

We have studied an analysis of OxyHb of fNIRS (a functional near-infrared spectroscopy) on the frontal cortex during vibrotactile stimuli, as shown in the previous papers [1, 5, 6, 7, 8]. As a result, we reported that the zero level of the OxyHb of fNIRS showed the parasympathetic activity (Figure 5), and total salivation in the vibrotactile stimulation of the 89 Hz frequency and 9.8 μm amplitude were the most effective.

Facial skin temperature increased from 32 to 34°C spend 3 min in the hand massage, and did 15 min in 89 Hz vibrotactile stimulation. Although 3 min stranger massage did not show the effective effect of total salivation, RR intervals increased from 670 to 1000 ms. However, over 3 min massage evoked the fatigue feeling. So, we tried 15 min 89 Hz vibrotactile stimulation. To increase RR intervals, we spent 3 min in the hand massage, but 15 min was spent in the 89 Hz vibrotactile stimulation; namely, an increase of facial skin temperature and RR interval will be effective in the 3 min hand massage.

We measured facial skin temperature and fNIRS on the frontal cortex during 3 min hand stimulation and during 3 and 15 min 89 Hz vibratory stimulation. We reported that the vibrotactile stimuli on the facial skin showed the near zero level of values of OxyHb, DeoxyHb, and TotalHb in fNIRS [1, 5, 6, 7, 8]. The OxyHb and DeoxyHb of brain circulation in the frontal cortex were reported to parallel the neuronal activity [2]. The finding is showed by the increased parasympathetic activity [1, 5, 6, 7, 8]. On the other hand, the decreased OxyHb (under zero level) showed the decreased neuronal activity with the decreased consumption of oxygen and metabolism, and the drowsy and sleepy conditions were shown by the decreased OxyHb during hand massages [13]. According to OxyHb activities of fNIRS on the frontal cortex, effects between stranger massage and resting condition are almost the same under zero level. Hand stimulation for 3 min may not show the increase of total salivation, except for the increase of facial skin temperatures, RR intervals of ECG and saliva amylase. However, RR interval and salivation were effective effort on 15 min 89 Hz vibrotactile stimulation, as shown in Figure 4B and the previous paper [5]. As over 3 min massage produced the fatigue feeling, we thought that repetitious stimuli may change the autonomic system and during hand massage, we tried hard not to get sleepy by talking. However, in the subject, this active feeling was decreased immediately and the subject felt sleepy.

4.4 Changes in an activity of saliva amylase

A stress is activated by the activation of sympathetic nerve, and an activity of saliva amylase is increased by a self-preservation response of a body; namely, the activity of amylase shows the activity of sympathetic nerve [14]. However, we may relate to amount of amylase because of their mass production after 15 min vibrotactile stimulation, as shown in Figure 6. The results showed the increased activation of saliva amylase related to amount of amylase, too. So, the increased saliva amylase was exhibited by about increase 2.5 times in 3 min hand stimulation and 89 Hz vibrotactile stimulation showed three times, as shown in Figure 6. This finding shows that subjects may be excited by stranger’s hand touching and then decrease of RR intervals (Figure 4B). On the other hand, it may be related to increase of amylase activity and amount of saliva in the 89 Hz vibrotactile stimulation, too.