A study of safety and tolerability of rotatory vestibular input for preschool children
Authors Su W, Lin C, Chang S
Received 31 October 2014
Accepted for publication 1 December 2014
Published 31 December 2014 Volume 2015:11 Pages 41—49
Checked for plagiarism Yes
Review by Single anonymous peer review
Peer reviewer comments 3
Editor who approved publication: Professor Wai Kwong Tang
Wen-Ching Su,1 Chin-Kai Lin,1 Shih-Chung Chang2,3
1Program of Early Intervention, Department of Early Childhood Education, National Taichung University of Education, Taichung, Taiwan; 2Department of Physical Medicine and Rehabilitation, Chung Shan Medical University Hospital, Taichung, Taiwan; 3School of Medicine, Chung Shan Medical University, Taichung, Taiwan
Abstract: The objectives of this study were to determine a safe rotatory vestibular stimulation input for preschool children and to study the effects of grade level and sex of preschool children during active, passive, clockwise, and counterclockwise rotation vestibular input. This study adopted purposive sampling with 120 children from three kindergarten levels (K1, K2, and K3) in Taiwan. The subjects ranged in age from 46 to 79 months of age (mean: 62.1 months; standard deviation =9.60). This study included testing with four types of vestibular rotations. The number, duration, and speed of rotations were recorded. The study found that the mean number of active rotations was 10.28; the mean duration of rotation was 24.17 seconds; and the mean speed was 2.29 seconds per rotation. The mean number of passive rotations was 23.04. The differences in number of rotations in clockwise, counterclockwise, active, and passive rotations were not statistically significant. Sex and grade level were not important related factors in the speed and time of active rotation. Different sexes, rotation methods (active, passive), and grades made significant differences in the number of rotations. The safety and tolerability of rotatory vestibular stimulation input data obtained in this study can provide useful reference data for therapists using sensory integration therapy.
Keywords: sensory integration, rotatory vestibular stimulation, tolerable input for rotatory vestibular stimulation
Children with vestibular function disability may have underlying developmental delays.1–4 However, some of these children may have hyperresponsivity (a greater-than-normal response) or hyporesponsivity (a lower-than-normal response) to vestibular input, which affects their motor skill performance in daily life.5 If a child appears to have a sensory-seeking vestibular stimulus and lacks the ability to discriminate between stimuli, he may have a strong tolerability to vestibular sensation and thus might seek dangerous antigravitational activities to meet his needs.6
When occupational therapists perform sensory integration intervention, they usually have different interventions for individual clients’ needs. Rotatory vestibular stimulation input is one of the most commonly used effective vestibular stimulation therapies, but there is still no reference value for rotatory vestibular input for occupational therapeutic intervention. Thus, it is important to establish a safe number of rotations and their duration as a reference for clinical application.
Ottenbacher7 reviewed the literature on vestibular stimulation, and indicated that vestibular stimulation activities included 1) rotatory stimulation, 2) linear or vertical acceleration, or 3) a combination of the two. Rotatory movement simulates the natural action the body uses when it acts as an axis for self-rotation.
Functions of vestibular stimulation
The vestibular system, which is part of the central nervous system, plays a key role in balance and spatial orientation. It is composed of the vestibular apparatus and the vestibular nerve. The vestibular receptor is located in the three semicircular canals, and the otolith is found in the inner ear.1 The vestibular apparatus, the major receptor in the human balance system, is located within the labyrinth in the inner ear in the temporal bone. The vestibular apparatus can be divided into the semicircular canals and the vestibule. The semicircular canals, horizontal, anterior, and posterior, are related to rotation and are perpendicular to each other.8,9 The flow of the endolymph in the semicircular canals touches the hair cells and detects the actions of rotation, acceleration, and deceleration.6 These dynamic messages are then sent to the vestibular nerve and the brain, and are integrated with other information to maintain balance.10 The vestibule is associated with balance,10 coordination,11 development of muscle tone,6,11,12 proximal joint stability,13 postural control,14,15 and plan of action. The vestibule is closely linked to the extraocular muscles, so it aids in development of visual motor integration.6,14 In addition, the vestibule can sense the spatial relationships of an individual within an environment and thus provides a sense of security16 and has a positive effect on an individual’s psychological development.
The application of assessments using rotatory vestibular stimulation
The most common diagnostic assessment for vestibular function includes use of the postrotary nystagmus test17 and clinical observation. The postrotary nystagmus test is used to identify whether a child has a vestibular disability.18 During the test, the subject is seated on a rotation disk, with his or her head fixed in a 30-degree angle forward, to ensure that the semicircular canals are horizontal.19 Next, the subject is rotated for ten clockwise or counterclockwise rotations, at 2 seconds per rotation. The subject is asked to gaze forward with both eyes, and the examiner observes the degree of nystagmus produced by the rotations.2,20 We modified this test in our study investigating the safety and tolerability of rotatory vestibular input for children.
The application of treatment using rotatory vestibular stimulation
Sensory integration therapy provides stimulus input for the vestibular, proprioceptive, and tactile systems.13 Vestibular input is commonly used by occupational therapists in sensory integration therapy. Rotatory activities include the use of a rotating swing, rotating disk, jump circling, somersault, side rolling, or front rolling. Children with hyperresponsivity respond with gravitational insecurity or aversion to movement. In this situation, occupational therapists halt activities with the rotating stimulus until the vestibular sensory adaptation is normal. According to Lin’s study,21 there were approximately 15% of children with hyporesponsivity issues. However, there were no data to indicate the number of children with hyporesponsivity for vestibular input. For most children with difficulty in sensory input and vestibular sensory-seeking, the therapist will provide vestibular input. If the rotatory vestibular stimulation input is excessive, it can cause an overload of stimulus to the brain, leading to an inability to concentrate,22 and causing the child to retreat and become defensive. It can also cause poor autonomic nervous system adaptation, such as unstable mood, dizziness, nausea, vomiting, paleness, hypotension, and postural imbalance.12
Occupational therapists observe these phenomena to determine whether there is an inappropriate reaction. However, it is not an easy job for a junior therapist to make an accurate observation of subtle change of sensory reaction. Thus, in sensory integration therapy, the number of rotations and controlling appropriate sensory input to produce an adaptive response are extremely important.
Since no studies have presented data on the safe number of rotations for children during vestibular testing, we designed a study to determine a safe, tolerable rotatory vestibular stimulation input for preschool children. In addition, we sought to investigate the effects of sex, grade, active and passive motion, and direction of rotation (clockwise, counterclockwise) on the number, time, and speed of rotations. Obtaining a reference value by evidence-based data ensures safe application of vestibular input in the intervention, and avoids poor adaptation.
Materials and methods
This study adopted purposive sampling with children from three kindergartens (K1, K2, and K3) in Taiwan. Subjects were excluded if they had a confirmed diagnosis of developmental delay, because poor sensory perception and insufficient motor skills may affect vestibular input judgment and body balance adjustments, which would affect the test results. Children who were disabled were also excluded because most of these children have deficiencies in cognitive ability or motor skills. Those with vestibular dysfunction, such as paroxysmal positional vertigo or vestibular neuritis, Meniere’s disease, migraine-associated vertigo, and childhood vertigo were also excluded from the study. Children with any of these conditions may become dizzy during rotation, which may be intolerable to them. Children with sensory deficits, such as myopia, hyperopia, strabismus, amblyopia, and sensorineural deafness, which may affect balance, were also excluded from the study. Children who had undergone prior sensory integration therapy were also excluded because their vestibular sensory systems have already been adjusted, which would affect the findings. We also excluded children who were in poor health on the day of the test; this included children with colds, injuries from falls, or unstable mood. Finally, children with a history of seizures were also excluded.
The final study group included 120 children, whose parents signed study consent forms. The subjects ranged in age from 46 to 79 months of age (mean: 62.1 months; standard deviation [SD] =9.60). There were 61 boys (50.8%) and 59 girls (49.2%); 49 were in K3 level classes (40.8%), with a mean age of 72.02 months (SD =3.13). Forty children (33.3%) were in K2 level classes, with a mean age of 59.83 months (SD =2.85). Thirty-one children were in level K1 classes (25.8%), and the mean age was 49.35 months (SD =1.95). Table 1 provides the demographic characteristics of the population in this study. There was no statistically significant difference in grade by sex (χ2 =0.91; P =0.64).
Table 1 Demographics of study participants
This study included testing with four vestibular rotations: active clockwise rotation vestibular input, active counterclockwise rotation vestibular input, passive clockwise rotation vestibular input, and passive counterclockwise rotation vestibular input. The number, duration, and speed of rotations were recorded.
The postrotary nystagmus test, as described in the section “The application of assessments using rotatory vestibular stimulation”, was adopted to measure vestibular input during passive rotation. The participants sat on a 60 cm diameter on the rotating disk. In active rotation, the participants stand on a 60 cm circle on the floor; the neck is fixed in a 30-degree forward angle, while the body acts as the axis for self-rotation. The child controls the speed of active rotation, and the investigator calculates the speed of rotation by recording the duration and the number of rotations.
Three thesis committees took training courses every year (which lasted at least three hours) from 2012 in order to meet the ethics requirements imposed by the Ministry of Science and Technology for grant application. The committees closely inspected all the study procedures to check that no harm was performed in a vulnerable population, examined if there were better ways to minimize discomfort and finally, checked that consent forms were signed by all parents. Then the investigator explained the purpose, procedure, and testing methods to the kindergarten teachers, who in turn explained the pertinent information to the parents when they arrived. Parents who consented to have their children receive the test according to the study protocol signed the study informed consent form. The parents and children were informed that this study was completely voluntary and refusal to participate would not impact the children’s right in the kindergarten in any way.
Our study adopted a one-on-one design during the rotation test to avoid peer competition and other factors that might unduly influence the study outcome. To reduce any anxiety caused by unfamiliarity with the study staff, the child’s teacher accompanied the child to the testing room. The test was conducted in the children’s kindergarten but not in their usual classrooms. The testing environment was a brightly lit classroom that was free from noise or other distractions. Before the test, the investigator had simple interactions with the children to reduce any nervousness and to build trust. The investigator also had an opportunity to observe and assess the physical condition of the children and could use clinical observations and demographic data to exclude any of the children who did not meet the test criteria. During the pretest interactions, the investigator also helped prepare the children for the test.
The test was performed in the morning, before the usual morning snack time. If the children had already eaten, the test would be postponed for an hour to avoid gastrointestinal upset. Four tests were completed in 2 days, with active rotation on one day and passive rotation the next day. Clockwise rotation and counterclockwise rotation were performed on the same day, with a half-hour interval between clockwise and counterclockwise rotations. The test was conducted in the following order: active clockwise, active counterclockwise, passive clockwise, and passive counterclockwise rotations. The investigator used a metering device to record the number of rotations and a stopwatch to record the duration of rotations. Then, he observed and recorded the child’s behavior after the rotations. The examination was halted if the child left the rotation disk during the test or complained of discomfort or of vertigo. It was also stopped if the children stopped the rotations on their own. The safety and tolerability of rotatory vestibular was defined in this study based on 1) the response of child, the child began to express discomfort, nausea, or dizziness or stopped on their own and 2) the phenomenon of autonomic nervous system, such as pale face, sweating, posture imbalance, and emotional instability.
During the test, if the child appeared to be in poor psychological or physiological health, for example, if he or she expressed discomfort, the test was stopped. The child could then rest, or another test time would be arranged. After the test, an appropriate amount of resistance exercise would be provided to relieve and adjust the results of vestibular stimulation; for example, squeezing a small ball, moving heavy objects, or pushing heavy objects. Children or their parents could ask to withdraw from the test at any time or refuse to participate in any test.
The Statistical Package for the Social Science (SPSS) (v 13.0; SPSS, Inc., Chicago, IL, USA) was used for data analysis. This study used statistical methods including descriptive statistics, dependent sample t-test, and mixed-design two-way analysis of variance (ANOVA). Scheffe tests were used for multiple post hoc comparisons when the variances were homogeneous. The level of statistical significance was set at 0.05.
Differences in the number of rotations
The results of the dependent sample t-test showed no significant differences in the number, duration, and speed of active clockwise and counterclockwise rotations. There also were no significant differences in the number of passive clockwise and counterclockwise rotations. Thus, this study used the mean number, time, and speed of clockwise and counterclockwise rotations to represent the number, time, and speed of rotations. The overall mean number of active rotations was 10.28 (SD =7.46), while the mean number of passive rotations was 23.04 (SD =31.4).
Our study adopted a two-way ANOVA approach with dependent samples. The grade times the mean number of rotations (F), including the number of active and passive rotations, was F=4.63 (P=0.01). The results indicated that the grade and the implementation had an interaction effect. Thus, simple main effect analysis was performed. Performance of simple main effect analysis included two steps. First, we used one-way ANOVA to analyze differences in the mean number of active rotations in children in different kindergarten levels, and differences of mean numbers of passive rotations for different levels. Second, we used the dependent sample t-test to analyze differences between the number of active and passive rotations among children in levels K3, K2, and K1.
There was a significant difference between the mean number of active rotations in the different kindergarten levels. F =13.53 (P=0.000) and the result of multiple post hoc comparisons indicated that the number of active rotations among those in level K3 was significantly greater than among those in levels K2 and K1, while there were no significant differences in levels K2 and K1 (Table 2). The mean number of passive rotations was significantly different in the three different levels; F =8.57 (P=0.000) and the result of multiple post hoc comparisons indicated that the number of active rotations in level K3 was significantly greater than in levels K2 and K1, while there was no significant difference between levels K2 and K1. The number of active passive rotations was similar in the different levels (Table 2).
Analysis of dependent sample t-test results showed that the number of active and passive rotations of levels K3, K2, and K1 were significantly different. The t-test values for levels K3, K2, and K1 were 3.78 (P=0.00), 2.89 (P=0.00), and 2.29 (P=0.03), respectively. Regardless of level, the number of passive rotations was significantly greater than was the number of active rotations. Effect sizes of differences of the number of active and passive rotations in levels K3, K2, and K1 were 2.24, 2.70, and 0.91, respectively. Thus, the number of active and passive rotations was greatest in children in level K2.
The mean number of active rotations among level K3 students was 14.05 (SD=9.79); among level K2 students the number was 8.5 (SD=3.35) and, among level K1 students, the number was 6.60 (SD =3.37). The mean number of passive rotations among level K3 students was 36 (SD=42.02); among level K2 students this was 17.55 (SD =20.07) and, among level K1 students, the number was 9.65 (SD=7.94).
In regard to sex, two-way dependent sample testing did not show an interaction effect; therefore, a main effect test was performed. The mean number of active rotations for boys was 11.67 (SD =9.16), while the mean number of active rotations for girls was 8.83 (SD=4.81). The mean number of passive rotations for boys was 28.84 (SD=37.49), and the mean number of passive rotations for girls was 17.04 (SD=22.29). After performing independent sample t-test analysis, the t-value of sex in the mean active rotations was 2.12 (P=0.04). The number of active rotations among boys was significantly greater than among girls. The t-value of the mean number of passive rotations was 2.09 (P=0.04); the number of passive rotations for boys was significantly greater than for girls (Table 3).
Table 3 Differences by sex in mean number of active and passive rotations
Differences in the duration of rotation
The duration of passive rotation was fixed at one rotation every 2 seconds; thus, only differences of the duration of active rotations were compared. After ANOVA, it was found that the mean duration of active rotations in the different kindergarten levels was F=13.64 (P=0.00); thus, there were significant differences in the time of active rotations among different grade levels. Results of post hoc comparison suggested that the duration of active rotations among children in level K3 was significantly greater than among children in levels K2 and K1; there was no significant difference between children in levels K2 and K1. The overall duration of active clockwise rotations was 24.17 seconds (SD =20.05). The mean duration of active clockwise rotations among grade K3 students was 34.39 seconds (SD =26.07) versus 19.18 seconds (SD =10.33) among level K2 students; the mean duration of active clockwise rotation of level K1 students was 14.46 seconds (SD =8.16) (Table 4).
Table 4 Variance analysis results for grades in duration of active rotations