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Psychology and Psychotechnics
Reference:
Efimova V.L., Nikolaeva N.O., Timofeeva E.A.
Cervical vestibular evoked potentials of children. Review of foreign research.
// Psychology and Psychotechnics.
2024. № 3.
P. 127-138.
DOI: 10.7256/2454-0722.2024.3.70977 EDN: FWAXOU URL: https://en.nbpublish.com/library_read_article.php?id=70977
Cervical vestibular evoked potentials of children. Review of foreign research.
DOI: 10.7256/2454-0722.2024.3.70977EDN: FWAXOUReceived: 08-06-2024Published: 28-09-2024Abstract: The growing interest of psychophysiologists in the role of the vestibular system in the development of children is due to its important role in the processes of sensorimotor integration. At the same time, in most cases, vestibular dysfunctions remain undetected by specialists, even in school-age children. The number of instrumental studies of vestibular function that can be used to examine children is limited. Cervical vestibular myogenic evoked potentials (cVEMP), which assess the sacculocervical reflex, are one of the promising types of electrophysiological diagnostics. The review is devoted to scientific research aimed at establishing normative data for analyzing the results of cVEMP in children without hearing impairment. It was found that there is no unified protocol for conducting cVEMP, since the following parameters may affect the results of the study: characteristics of the acoustic stimulus; the length of the subject's neck; the way in which tonic tension of the sternocleidomastoid muscle is caused; anatomical features of the auditory canal and other factors. The study of cVEMP is non-invasive, takes no more than 15 minutes, and is well tolerated by children. Diagnosis can be carried out from the first days of life. The diagnostic results allow us to draw conclusions about the degree of myelination of the sacculocervical reflex pathway. There is evidence that myelination is delayed in premature infants, children with the effects of asphyxia. It has been shown that the consequences of this deficiency do not disappear, they manifest themselves in preschool and school-age children with attention deficit hyperactivity disorder, learning difficulties, and Down syndrome. Further research will contribute to the development of a unified CMVP protocol for the examination of children, which will make it possible to identify children with risk of developing disorders and conduct early intervention already in infancy. Keywords: vestibulocervical reflex, cVEMP, sacculocervical reflex, vestibular system, children, learning difficulties, vestibular dysfunctions, developmental disorders, sensorimotor integration, sacculusThis article is automatically translated. Introduction In recent decades, the interest of psychophysiologists in the role of the vestibular system in the development of sensorimotor integration in children has grown. Assumptions that vestibular dysfunctions can make a significant contribution to the formation of not only motor but also cognitive developmental disorders in children were put forward in the 1970s by an occupational therapist Ayres J. A [3]. It is known that the vestibular system is anatomically and functionally formed even before birth, any deviations in its functioning can affect the formation of motor skills and the picture of the child's world. Therefore, the relevance of assessing the functional state of the vestibular system in children is beyond doubt. The difficulties are due to the fact that not all methods of vestibular diagnosis are well tolerated by children, in addition, some methods involve taking into account the subjective reaction of the subject to the examination. Due to limited speech abilities, children often cannot talk about their feelings, so it is important to use studies in which the subject takes a passive part. It is also important to minimize discomfort during diagnosis. One of such promising instrumental studies is the assessment of the sacculocervical reflex by registering cervical vestibular myogenic evoked potentials (hereinafter - cVMVP). This study allows us to assess the quality of functioning of the otolithic part of the vestibular apparatus [1,12,17,21]. This study has been used relatively recently to identify vestibular dysfunctions in children. As the analysis of the scientific literature shows, almost every laboratory that conducts cVMVP for children uses its own standards. The purpose of this review was to study the possible causes of the existing disagreements about the norms of CMVP in children.
Discussion cVMVP is a complex response of the sacculus of the vestibular apparatus and the lower part of the vestibular tract to a loud sound stimulus – the sacculocervical reflex, which is part of the vestibulocervical reflex. This reflex is triggered even in deaf subjects, but is absent in people with a damaged or surgically removed sacculus [9]. This study was first used in 1992 to examine adult patients with vestibular disorders [7]. Two early components are distinguished on the cVMVP curve: positive P1 and negative N1. Since the first studies revealed that the latency of peak P1 is 13 ms, and the latency of peak N1 is 23 ms, in some articles these peaks are called P13 and N23. However, many researchers still use the names P1 and N1. Some laboratories also take into account the difference between the latency and amplitude indicators on the left and on the right – the symmetry of the responses[2,30]. In published studies, the amplitude of peaks P1 and N1 and the interval P1N1 are also often estimated, but there is evidence that the amplitude depends on the intensity of the stimulus and the level of tonic tension of the muscle. In addition, there is variability in amplitude during repeated studies, depending on age. Therefore, the possibilities of using amplitude parameters in clinical practice are limited [22]. More often, cVMVP is performed in children with hearing impairments to identify concomitant disorders in the vestibular system [28,15]. cVMVP can be registered in infants in the first days of life. It has been shown that the registration of cVMVP in newborns with various hearing and vestibular disorders provides useful information about vestibular function, and can help improve the rehabilitation of children at risk of developmental delay [26]. Over the past decades, a number of studies have shown deviations of cVMVP indicators from the norm in various groups of children with normal hearing, but with developmental disabilities. Thus, changes in cVMVP indicators were detected in children with attention deficit hyperactivity disorder. The authors propose to include this study in a battery of tests to identify children with this diagnosis [16]. Changes in cVMVP were also revealed in a study of 30 schoolchildren with learning difficulties [8]. The study of children with Down syndrome involved 15 people aged 9-11 years and 15 healthy children of the same age. In children with Down syndrome, the latency of N1 is significantly higher and the amplitude is significantly lower than in children of the control group [18]. It was found that premature infants also have features of cVMVP. The study included 50 premature newborns born less than 37 weeks pregnant. The control group consisted of 20 healthy full-term newborns. cVMVP was registered in all full-term infants. The latency of P1 and N1 was significantly higher in 24 premature infants, and cVMVP was absent in 5 children. Thus, there is a significant difference between the indicators of CMVP in premature and full-term infants. Abnormal indicators of the functioning of the vestibular system are mainly characteristic of premature infants with the effects of asphyxia. There was no association between increased cVMVP latency and gestation period, birth weight, hemoglobin and bilirubin levels, phototherapy, intracranial hemorrhages, seizures, sepsis, ototoxic drugs, blood transfusion, artificial ventilation, retinopathy of prematurity, bronchopulmonary dysplasia and respiratory distress syndrome [11]. cVMVS are also used to assess the long-term effects of prematurity. In one study, cVMVP was evaluated in 30 children aged 5.5 – 6 years who were born prematurely. The indicators were compared with the results of 20 full-term infants of the same age. The latency of peaks P1 and N1 in the group of premature infants was significantly higher than in the control group. The hearing condition, as well as the gender of the subjects, did not affect the results. The authors concluded that cVMVP reflects disorders in the development of the nervous system, which are manifested in the functional immaturity of the sacculocervical reflex pathway, namely, insufficient myelination. The cVMVP method can be used as a tool for long-term monitoring of the effects of premature birth on child development [10]. The question remains debatable as to which indicators of CMVP can be considered normative for children. An analysis of scientific articles on the norms of cVMVP in children without hearing impairment showed significant differences in the views of several laboratories about the norms. The results of the literature analysis are presented in Table 1.
Table 1. CMVP standards according to scientific research data 2006-2023
As can be seen from the table, in most cases, the sacculocervical reflex is well evoked in children. However, there is a significant variation in the results obtained: the latency of peaks P1 and N1, as well as the amplitude. Not all laboratories evaluate the symmetry of responses - the difference between the indicators on the left and on the right. It has been shown that cVMVP can be registered in children already in the first days of life. The study involved 20 healthy newborns and 20 adults with normal hearing. A comparison of the characteristics of cVMVP in healthy newborns and adults revealed a slight difference in the response rate and latency of P1. However, there were significant differences in N1 latency, P1-N1 peak interval, and P1-N1 amplitude between newborns and adults. It was concluded that an increase in cVMVP latency or lack of response in newborns may indicate incomplete maturity of the sacculocervical reflex pathway as a result of insufficient myelination [6]. The same authors showed that in healthy newborns with normal hearing by the fifth day of life, the average latency of P1 is 13.3+/-0.8ms, which corresponds to the indicators of an adult [34]. In another study, which compared the cVMVP indicators of school-age children and adults, a statistically significant increase in latency and a smaller amplitude in young children was revealed compared with the normative data for adults. The latency of P1 in children was 17.5 ± 1.41 [14]. According to some data, the latency of cVMVP peaks does not depend on age [4]. A significant disadvantage of most studies is that the groups of subjects are mostly small, which can lead to incorrect conclusions about the influence of age on diagnostic results. The way out of this situation may be to distribute the subjects into more age-homogeneous groups and increase the sample size. In one study, 280 healthy volunteers aged 10 to 85 years were divided into seven age groups: 10-20, 20-30, 30-40, 40-50, 50-60, 60-70 years old and over 70 years old. It has been shown that significant changes in the latency and amplitude of cVMVP are detected only in the group over 50 years old: latency increases with age, and the amplitude and thresholds for registration of evoked potentials decrease. However, children under the age of 10 did not participate in this study [27]. A number of studies have shown that, starting from preschool age and up to the period of adulthood, CMVP indicators change, therefore, the development of standards for children is required [1,29]. One of the studies aimed at establishing pediatric standards of CMVP, in which the sample consisted of 118 subjects, was conducted in 2023. This study presents normative data on cVMVP for children aged 6 months to 15 years, taking into account age and gender, for air and bone conduction of sound. It has been shown that at the age of up to 15 years, cVMVP can be obtained equally successfully with both stimulation modes [33]. The analysis of studies shows that the results of cVMVP can be influenced not only by the age of the subjects, but also by the characteristics of the sound stimulus. A number of studies use clicking as an incentive. In other studies, a tone sending with a frequency of 500 or 750 Hz is used. The intensity of the sound stimulus can vary from 80 to 130 dB, depending on the device and other parameters of the stimulus. Latency is considered a reproducible characteristic of cVMVP, which does not depend on the intensity of the stimulus and the level of tonic contraction. But there is evidence that the latency of P1 in response to a click stimulus is always lower than for a tone premise [22,23,32]. Since each laboratory can use different incentives to conduct CMVP, the results presented in the articles are quite difficult to compare with each other. Thus, 30 subjects aged 3 to 11 years took part in one of the first works devoted to determining the standards of CMVP for children. Clicks with an intensity of 80, 85 and 90 dB were used as a stimulus. To analyze the data, the subjects were divided into four age groups. Of the 30 children tested, all subjects had bilateral reflexes, and 28 out of 30 subjects (93%) had symmetrical responses. The average latency values of peaks P1 and N1 were 11.3 ms (+/- 1.3 ms) and 17.6 ms (+/- 1.4 ms), respectively. The average amplitude of P1-N1 was 122 Mv (68 MV) [19]. Thus, the authors of the study found that the latency and peak of P1 in children are significantly lower than in adults. But this conclusion was not made in all laboratories. In 2006, another study was published on the standards of CMVP in children. It was attended by 40 children aged 3-15 years without hearing impairment. The parameters of the sound stimulus were different: it was a tone parcel of 500 Hz, with an intensity of 130 dB. cVMVP were recorded in all subjects. In the preschool group, the average latencies of P1 and N1, respectively, were 16.13 (+/-2.12)ms and 21.17 (+/-2.77)ms; the average amplitude ratio was 28.49 (+/-18.10). In the group of school-age children, the average values of P1 and N1 were 16.14 (+/-3.48) ms and 21.78 (+/-3.39)ms, respectively, and the average amplitude ratio was 20.44 (+/-13.24). A comparison of the durations and amplitude ratios between the groups of children and the control group of adults did not reveal any significant differences [24]. There is a study that shows that the optimal incentive for children to have cVMVP is a 750 Hz tonal parcel. The study involved 10 children 4-9 years old; 10 adolescents 10-12 years old and 10 young adults 20-29 years old. The authors of the study showed that there is no difference in indicators between the age groups [25]. The difference in the results of the study may also be caused by differences in the procedure for conducting the study. For example, the position of the subject's body during diagnosis. To register cVMVP, it is necessary to induce a tonic contraction of the sternocleidomastoid muscle. In some laboratories, this is achieved by moving the patient's head to the side in a sitting position. Another option for conducting the study: muscle contraction occurs at the moment of lifting the head up from the prone position. For example, this option was used in Singapore when conducting a study of school-age children [20].
However, it is believed that the test parameters do not change depending on whether the tonic tension of the muscle is provided by lifting or turning the head [5]. Another hypothesis about the causes of the variability of cVMVP results in scientific articles is related to the difference in neck length in children and adults. It can be assumed that the latency of the evoked potentials will depend on it, since the result of the study is associated with the tone of the sternocleidomastoid muscle. In one study, the results of cVMVP tests in 14 healthy children, 7 healthy adolescents and 14 healthy adults were analyzed for correlation with neck length, which was measured as the distance from a line running vertically from the tip of the mastoid process to a horizontal plane passing through the collarbone. The indicators of children, adolescents and adults differed significantly in latency P1, latency N1 and the interval P1-N1. A positive correlation between neck length and cVMVP latency was observed when the neck length was <15.3 cm, while when exceeding this level, the length of the neck did not affect the latency of cVMVP [31]. The type of headphones for conducting cVMVP is usually not described in the articles. But some articles are accompanied by photos where you can see the installation locations of the electrodes and the type of headphones. Some labs use in-ear headphones that fit inside the ear canal. In other laboratories, headphones are used, which are located on top of the auricles [17]. There is evidence that the shape of the auditory canal can affect the performance of CMVP in children. This suggests that the type of headphones may also influence the results of the study [13]. In addition to the differences in research described above, there are additional diagnostic conditions. For the convenience of diagnosis for young children, some laboratories offer the use of sedation. But in most laboratories, the examination is carried out in a waking state [14]. Conclusions. An analysis of published studies shows the following. The idea that each laboratory can use its own data on the norms of CMVP in children is based on the possible influence of the features of the research procedure on its results. These may be the following factors: 1. Acoustic characteristics of the stimulus: click / tone 500 Hz / tone 750 Hz; 90/30 Db 2. The length of the subject's neck 3. The method by which tonic tension of the sternocleidomastoid muscle is caused 4. Presence or absence of sedation 5. Anatomical features of the ear canal (possibly the type of headphones)
Due to the above-described features of cVMVP, in scientific articles, as well as in the conclusions that the subjects receive, it is necessary to describe in detail all the details of the study that may affect its results. When assessing the dynamics of myelination of the sacculocevical pathway in children, it is important to conduct a study in compliance with the same conditions as in the initial study. It is advisable to do this in the same laboratory. An analysis of the literature allows us to conclude that cVMVS are a promising, non-invasive and informative way to assess the functioning of the otolithic part of the vestibular apparatus in children. This diagnosis takes no more than 15 minutes and is well tolerated by children of any age. Further research is required, which may lead to the creation of unified protocols for the implementation of CMVP for children. References
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