Salivary Alpha-Amylase Reactivity under Psycho-Physiological Stress. A Nonverbal Communication Measurement Tool?

doi:10.4236/jbbs.2011.11003

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Journal of Behavioral and Brain Science, 2011, 1, 12-15

doi:10.4236/jbbs.2011.11003 Published Online February 2011 (http://www.SciRP.org/journal/jbbs)

Salivary Alpha-Amylase Reactivity under

Psycho-Physiological Stress. A Nonverbal

Communication Measurement Tool?

Takuji Inagaki1, Masa Ieda2, Satoko Yamashita2, Tsuyoshi Miyaoka2, Jun Horiguchi 2

1Shimane Universi t y, Faculty of Education, Department of Psychol o gy an d Special Support Educ ati o n,

Nishikawatsu, Matsue, Shimane, Japan

2Shimane Universi t y, Faculty of Medi ci ne, Department of Psychiatry, Shimane, Japan

E-mail: [email protected] u.ac.jp

Received January 25, 2011; revised February 12, 2011; accepted February 17, 2011

Abstract

Previous studies have shown that changes in salivary alpha-amylase (sAA) levels are dependent on psycho-

social stress stimulation and reflect the activity of the sympathetic nervous system. sAA measurement can be

performed easily and quickly; therefore, it may be useful for evaluating psychosocial or physical stress. The

aim of this preliminary study was to examine the use of sAA measurements as objective indicators of psy-

chosocial and/or physical stress levels by examining sAA changes in volunteers subjected to conditions

similar to those suffered by children with severe motor and intellectual disabilities and cerebral paralysis.

Twelve healthy volunteers were required to not move or speak, as is found in patients suffering from total

paralysis, for 30 min. Saliva samples were taken at three points, and sAA activity was measured using a

hand-held monitor before the test, immediately after the test, and 10 min after the test. In the present study, a

marked increase in sAA activity due to physiological stress and a rapid return to the baseline level were ob-

served. Many subjects felt body pain and mental distress. This measurement method is useful for evaluating

stress in children with severe motor and intellectual disabilities, who can not fully express their emotions or

communicate with their caregivers.

Keywords: Nonverbal Communication, Psychosocial Stress, Physical Stress, Salivary Alpha-Amylase, Se-

vere Motor and Intellectual Disabilities

1. Introduction

Salivary alpha-amylase (sAA) has been suggested to

reflect stress-related body changes. Psychosocial stress

increases the release of salivary alpha-amylase, which

reflects the activity of the sympathetic-adrenal-medullary

(SAM) system [1-3]. Therefore, it is supposed that sAA

measurement is a useful tool for evaluating the SAM

system. In addition, previous studies examining the re-

sponse of sAA levels to SAM system activity showed

that increased sAA levels were correlated with increased

plasma catecholamine, indicating sympathetic nervous

system activation [4,5]. To date, numerous studies have

shown that changes in sAA levels are dependent on

stress stimuli [1,6-10].

As far as we know, few studies have investigated

psychosocial or physical stress in children with severe

motor and intellectual disabilities such as patients with

severe cerebral palsy. Such patients usually can not fully

communicate with others or describe their emotions. It is

therefore difficult to objectively evaluate their emotional

and physical state. sAA measurement can be performed

easily and quickly, and therefore, could be used to aid

the evaluation of the psychosocial and/or physical stress

levels of such patients.

In special support education, it is very important to be

able to evaluate and understand the level of psychosocial

and/or physical stress (distress) experienced by a child,

particularly in children with severe motor and intellectual

disabilities. The measurement of sAA is expected to be

useful as a nonverbal communication procedure for chil-

dren with severe motor and intellectual disabilities.

The aim of this preliminary study was to examine the

use of sAA measurements as objective indicators of

T. INAGAKI ET AL.

psychosocial and physical stress levels by examining

sAA changes in volunteers subjected to conditions simi-

lar to those suffered by children with severe motor and

intellectual disabilities and cerebral paralysis; i.e., the

participants were ordered to lie down with their face

pointing upward and to not move or speak for thirty

minutes.

2. Methods

The study subjects were recruited at Shimane University.

Twelve healthy student volunteers (mean age: 20.8  1.8

years; 7 females; 5 males) were recruited from the De-

partment of Psychology and Special Support Education

at the university. All subjects gave their written informed

consent before participating in this study after the pur-

pose and procedure had been fully explained to them.

All subjects were medication-free and had no history of

neurological or psychiatric disorders and drug/alcohol

abuse. They were also not taking any medication or

cigarette. We excluded the subjects with cardiovascular

diseases that caused autonomic dysfunction, chronic dis-

eases such as cancer or diabetes mellitus or hyperlipide-

mia. The subjects were told to refrain from brushing their

teeth or eating for at least 60 min before the measure-

ment session [8]. Using the previously developed method,

one-time saliva sampling collection was conducted dur-

ing the same time interval (2:00-3:00 PM) to minimize

any effects of circadian rhythms.

3. Results

We used a hand-held monitor (Nipro Co., Japan) and

reagent paper to measure enzymatic sAA activity. This

measurement method can be performed easily and

quickly and is a convenient and useful objective indica-

tor for medical and educational practice. The hand-held

monitor consisted of a disposable test strip and a monitor

[11,12]. This method for analyzing sAA has previously

been evaluated and used [13,14].

To assess autonomic functional changes, resting heart

rate (HR) was measured in all subjects during the same

time interval whilst they were lying in a recumbent posi-

tion, as heart rate is thought to be an indicator of auto-

nomic (sympathetic and parasympathetic) function.

The test consisted of three periods in which the sub-

jects remained in a recumbent position: 10 min resting

time (pre-test), 30 min fixed position time (test), and 10

min resting time (post-test). The subjects rested in a re-

cumbent position on the floor for 10 min before the main

part of the test. Then, they were required to not move or

speak, as is seen in patients suffering from total paralysis,

for 30 min. They remained in the fixed position, alert,

and quiet for 30 min. Then, they were ordered to remain

lying down and rest for a further 10 min.

In addition, all subjects were asked whether they were

experiencing any body pain or mental distress. Their pain

and mental distress were estimated using a VAS (visual

analogue scale). The VAS score was obtained from sub-

jects who felt body pain in some body portion or mental

distress at the end of the test. Subjects reported the level

of pain and mental distress as VAS score.

Saliva samples were taken before the test, after the

subjects had been lying in the fixed position for 30 min,

and at 10 min after the test. Heart rate was simultane-

ously measured in all subjects at the three time points.

The results are expressed as means  SD. To compare

the clinical variables at the three time points, the data were

analyzed with repeated measures ANOVA by applying the

SNK correction using Statview 5.01 (SAS Institute Inc.,

USA). The level of significance was set at p < 0.05.

The volunteers’ mean pre-test, test, and post-test sAA

levels were 32.2  16.6 (kU/l) (range, 17-69), 61.5 

47.2 (range, 24-193), and 34.9  11.8 (range, 18-56),

respectively. Significant differences were found using

the ANOVA among three points (F = 4.88, p = 0.018),

therefore, SNK correction was conducted. There were

significant differences between the test and pre-test sAA

levels (p < 0.05), and between the test and post-test sAA

levels of (p < 0.05). The salivary alpha-amylase level

increased significantly during the fixed positioning pe-

riod and had returned to the baseline by 10 min after the

test (Figure 1).

The mean pre-test, test, and post-test heart rates were

64.8  11.7, 63.5  8.3, and 61.2  10.4, respectively. In

contrast, heart rate did not change between the stress and

the rest conditions (Table 1). Ten subjects (77%) com-

plained of body pain, particularly in the head, lumbar,

hands, and heel. The mean VAS score of them for pain

Figure 1. Changes in salivary alpha-amylase activity after

remaining in a fixed position for 30 mins.

14 T. INAGAKI ET AL.

Table 1. Psycho-physiological stress test results.

Time (min)

(Pre-test)

(Test)

(Post-test)

Salivary alpha-amylase

(kU/L) 32.2 ± 16.6 61.5 ± 47.2* 34.9 ± 11.8✝

Heart rate 64.8 ± 11.7 63.5 ± 8.3 61.2 ± 10.4

*p < 0.05; Pre-test v.s. Test ✝p < 0.05; Test v.s. Post-test

was 54. Mental distress was revealed in five subjects

(38%) and the mean VAS score of them for mental dis-

tress was 63.

4. Discussion

In the present study, a marked increase in sAA activity

due to physiological stress was observed during the main

part of the test followed by a rapid return to the baseline

level. Many subjects felt body pain and mental distress.

A portable sAA activity monitor has recently been

developed, and several investigations have suggested that

sAA reflects mental stress or have shown a positive rela-

tionship between the sAA increases and sympathetic

activity.

Nater et al. [8] reported a positive relationship be-

tween the sAA level and sympathetic tone, which was

assessed using heart rate variability parameters during

periods of stress. Previous reports have also indicated

that the sympathetic nervous system plays a predominant

role in the sAA secretion observed under psychosocial

stress [2,3]. Several reports have demonstrated that psy-

chosocial stress increases the release of sAA and that a

marked increase in sAA occurs following exposure to

psychosocial stress, indicating that sAA activation is

stress-dependent.

Shirasaki et al. [5] reported that sAA was significantly

correlated with the VAS pain scale in patients with

chronic pain. In addition, after pain therapy (epidural

block), sAA activity was reduced in combination with a

decrease in pain intensity but not SAM activity. There-

fore, they suggested that sAA reflects the activity of the

SAM system during pain-induced stress and that sAA

measurements might be a good index for the objective

assessment of pain intensity.

In psychiatric patients, we previously reported that the

sAA activity of schizophrenic patients was significantly

higher than that of control subjects, and the correlation

between sAA level and psychiatric symptoms was highly

significant [15].

These findings suggest that sAA correlates with psy-

chiatric or/and psychosocial stress intensity.

To the best of our knowledge, only one study has

proposed using biochemical measurements of sAA activ-

ity as a non-verbal communication method for interact-

ing with children with severe motor and intellectual dis-

abilities [13]. The physiological conditions of these chil-

dren were evaluated by measuring their sAA activity,

which required the daily insertion and removal of tra-

cheostomy tubes or gastric tubes, and sAA was measured

before and after medical care. As a result, they found that

sAA activity was increased after medical care.

We performed the present study as a preliminary in-

vestigation aimed at clarifying whether this method

could be used in clinical practice to evaluate the levels of

psychosocial and/or physical stress in children with se-

vere and intellectual disabilities, who are not able to

move or complain about discomfort and/or distress. Such

children can not move their bodies for themselves and

may feel distress and pain when their body position is

changed by assistance.

In this study, we examined the changes in the sAA

levels of healthy volunteers subjected to conditions that

were designed to reflect those experienced by children in

the cerebral paralytic state, as it was impossible to di-

rectly examine the disabled children in fixed position for

long time. There are no studies which examine the stress

marker in the long-period fixed body position. We sup-

posed that this particular situation could reflect the psy-

chosocial and/or physical stress of the disabled children.

The present results also suggest that the physiological

conditions of patients who remain in a fixed position for

a long period, who are considered to be in a similar con-

dition to paralytic children/patients, can be evaluated by

measuring their sAA levels.

On the basis of our results, we would like to use our

method in clinical practice in future.

5. Conclusion

Salivary alpha-amylase is a useful parameter for evalu-

ating psychophysiological stress in children with dis-

abilities, since it is easy to measure. Thus, the changes in

the sAA levels observed in the present study may reflect

the level of mental stress experienced. Children with

severe and intellectual disabilities can not fully express

their emotions or communicate with their caregivers.

This measurement method is useful for evaluating the

stress levels of such patients.

6. Acknowledgments

The authors would like to thank the university students

of Shimane University Faculty of Education for their

support.

T. INAGAKI ET AL.

7. Conflicts of interest

The authors state that there are no conflicts of interests

that relate to this research.

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