Many reviews have documented the adverse effects of noise on children's health, but the international scientific community was previously unfamiliar with noise research in Central and Eastern Europe (CEE), South-East Europe (SEE), and Newly Independent States (NIS). The aim of this review was to present studies on the effects of noise on children's health, conducted in aforementioned countries in the second half of the 20 th century, interpret their findings, and criticize their methodology and results wherever possible. This review focused on 30 papers published in national journals in the period from 1965 to 2000. By design, 22 studies were observational and cross-sectional, and eight studies were experimental. The outcomes under the study included auditory changes, stress reactions, sleep disturbances, school performance, upright posture, and vegetative functions. Researchers from CEE, SEE, and NIS were the pioneers in the assessment of noise-induced changes of vegetative functions and blood pressure of children in urban areas, as well as of infants exposed to noise in incubators. Future research should focus on intervention studies and follow-up of children's health in relation to noise exposure.
Keywords: Acoustics, auditory threshold, blood pressure, children, incubators, infants, noise, schools, sleep
|How to cite this article:|
Paunovic K. Noise and children's health: Research in Central, Eastern and South-Eastern Europe and Newly Independent States. Noise Health 2013;15:32-41
| Introduction|| |
Sound is a global phenomenon in the environment. The ability to hear sounds starts in utero and remains generally stable throughout the lifespan; it is well preserved during sleep and unaffected in an unconscious state. Sound becomes noise when subjects perceive it as unwanted,  when it produces undesired physiological or psychological effects, and when it interferes with the social ends of an individual or a group. 
Environmental noise is emitted from traffic, industrial facilities, and neighborhood. Children, nevertheless, may be exposed to additional sources of noise, including toys, music and communication devices, educational, recreational, and entertainment facilities. , Public authorities, physicians, and parents should be aware of the potentially hazardous effects of such exposure, and should be encouraged to protect children from noise in their environment.
Several reviews and reports published in the last 10 years have created a large pool of knowledge on the association between noise exposure and children's health. ,,,,,,, The adverse effects of noise include cognitive impairment, sleep disturbances, annoyance, adverse psychological reactions, and changes in vegetative functions. Physiological and psychological mechanisms linking noise exposure and these effects remain to be clarified. ,,,
The scientific community was previously not familiar with noise-related research conducted in the 20 th century in Central and Eastern Europe (CEE), South-East Europe (SEE), and Newly Independent States (NIS). This could have occurred due to political blockades or language barriers. This journey into the past resulted in the re-discovery of the long-forgotten or unheard-of studies. The aim of this review was to present studies on the effects of noise on children's health, conducted in CEE, SEE, and NIS countries in the second half of the 20 th century, interpret their findings, and criticize their methodology and results wherever possible.
| Methods|| |
This review includes studies on the effects of environmental noise on children published from 1965-2000 in CEE, SEE, and NIS. The author searched through medical and scientific databases (PubMed, Embase, Scopus, BioMed Central, Web of Science, Google Scholar, and Science Direct). Key search terms were noise, environmental noise, road traffic, acoustics, school, kindergarten, incubator, children, health, hearing, blood pressure, sleep, annoyance, school performance. CEE-an countries, SEE-an countries, and NIS were included into search, in alphabetical order: Armenia, Azerbaijan, Belarus, Bulgaria, Bosnia and Herzegovina, Croatia, Czech Republic, Czechoslovakia (former), Georgia, German Democratic Republic (former), Hungary, Kazakhstan, Former Yugoslav Republic of Macedonia, Moldova, Montenegro, Poland, Romania, Russian Federation, the Union of Soviet Socialist Republics USSR (former), Serbia, Slovakia, Slovenia, Ukraine, and Yugoslavia (former).
This author was determined to present the papers that were unavailable in English, difficult to find, and unknown to the scientific community. The selected scientific papers, therefore, had to fulfill the following criteria: Publication in national languages, in peer-reviewed Journals, and between 1965 and 2000.
In total, 30 papers were identified for this review, including four papers from Czech Republic (former Czechoslovakia), two papers from former German Democratic Republic, 10 papers from Poland, two papers from Russian Federation (former USSR), and 12 papers from Slovak Republic (former Czechoslovakia). The papers were written in Czech, Slovak, Polish, Russian, and German; most of them contained abstracts in English. Noise units are reported exactly as stated in original papers, either as dB (unit of sound pressure level), or as dB (A) (unit of A-weighted sound pressure level).
| Results and Discussion|| |
The outcomes under study were noise measurements and exposure assessment, hearing, psychological reactions, sleep disturbance, vegetative functions, blood pressure, and the effects on newborns. The reviewed studies were grouped into five sections, based on their main outcomes. By design, 22 studies were cross-sectional epidemiological surveys, and eight studies were experimental. [Table 1],[Table 2] and [Table 3] systematize some of the reviewed studies in chronological order.
|Table 1: Studies on the effects of noise on children's hearing in Central and Eastern Europe, South-East Europe, and Newly independent states|
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|Table 2: Studies on the effects of noise on children's psychological reactions and sleep disturbance in Central and Eastern Europe, South-East Europe, and newly independent states|
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|Table 3: Studies on the effects of noise on children's vegetative functions and blood pressure in Central and Eastern Europe, South-East Europe, and newly independent states|
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Noise measurements and exposure assessment
Systematic noise research started in CEE, SEE, and NIS countries in the 1960s. Some of the earliest studies concentrated on noise measurements in urban settings, primarily near schools, ,, as well as near kindergartens. , For example, noise measurements were performed outside and inside two primary schools in Prague (Czech Republic, former Czechoslovakia).  One school was built near a busy highway; whereas the other was localized in a quiet area. Noise levels were measured from 8 am to 4 pm on several occasions during working days. In the noisy area, the average equivalent noise levels outside school were 80 dB (A) in the morning, 75 dB (A) at noon, and 78 dB (A) in the afternoon. At the same time, maximal noise levels outside a quiet school ranged from 60 dB (A) in the morning, to 57 dB (A) at noon, and to 60 dB (A) in the afternoon. Noise levels inside the classrooms of a noisy school were 56 dB (A) (with closed windows) and 69 dB (A) (with open windows). An average noise level inside the classrooms of a quiet school was 50 dB (A), regardless of windows being open or closed. 
Noise levels were also measured outside thirty schools in Szczecin (Poland). Noise levels outside two-thirds of all the investigated schools exceeded the established limits.  The authors concluded that the main problem was the construction of new schools using building materials with low insulating power. They proposed that the authorities place acoustic screens and plant vegetation around newly built schools in order to reduce exposure to noise. 
The acoustics of nurseries, kindergartens, and schools was widely examined in Poland.  More than two-thirds of all the examined day-care centers for children were located in adequate acoustic areas with noise levels below 55 dB (A). The acoustical situation was unfavorable only in day-care centers that were adapted from premises built for other purposes, in objects built at the beginning of the 20 th century, and in objects located near busy streets, railway stations, or industrial plants.  However, the acoustics inside classrooms and children's rooms was not satisfactory. Outdoor noise caused acoustical problems in 18% of rooms, whereas indoor noise caused problems in 37% of rooms.  As expected, indoor noise levels depended on children's activities. Equivalent noise levels inside preschools and schools were similar in corridors (40-45 dB(A)), but were significantly higher in day-care rooms of preschool facilities (upto 57 dB(A)). The main causes of indoor noise in children's educational facilities were overcrowding (large number of pupils per class), inappropriate arrangement of rooms (classrooms, service rooms, dining rooms), poor insulation (doors and windows), poor organization of work, and inadequate use of technical protective means. ,
In other elementary schools, the highest noise levels were measured in corridors during breaks (between 60 and 95 dB; the most frequent noise level was 80 dB), followed by teacher's rooms, doctor's offices, director's rooms, reading rooms, and classrooms situated near a gym. As expected, noise levels decreased during lessons in all rooms, but the corridors remained the noisiest, with noise levels upto 65 dB.  The researchers pursued an additional study to explore the acoustical differences between elementary and secondary schools. Noise levels in secondary schools were by 5-10 dB (A) lower than in elementary schools, both in corridors and classrooms, regardless of the time of measurement (during lessons or school breaks).  Noise levels during lessons depended mainly on the number of pupils, manner of teaching, type of classroom activity, duration of lessons, and the day of the week. Work in groups was by 5-7 dB (A) noisier than classical teaching and individual activity; classes with more than 30 pupils were by 3 dB (A) noisier than classes containing less than 25 pupils. Noise levels inside classrooms were unrelated to the subject of teaching and the year of schooling. 
In high schools in Bratislava (Slovak Republic, former Czechoslovakia), noise levels were measured inside classrooms on several occasions (in summer and winter), at the time interval between 8 am and 1 pm, with windows open and closed.  Schools were located 30-50 meters from the street. Minimal noise levels in classrooms with closed windows exceeded 45 dB (A) in all schools; and half of all the measured values ranged 50-60 dB (A). The acoustical situation was worse with open windows, because more than a half of all obtained values ranged between 60 and 75 dB (A).  The author highlighted that the main problem was the localization of schools, which should be addressed during the planning process, as well as during preventive sanitary supervisions of the schools. 
Noise exposure was measured during school lessons  and during activities in nurseries or kindergartens. , In Bratislava (Slovak Republic, former Czechoslovakia), noise levels in ten primary schools ranged 27-70 dB (A) [average equivalent noise level was 65 dB (A)], whereas noise levels in ten kindergartens ranged 36-80 dB (A) [average equivalent noise level equaled 80 dB (A)]. The highest noise levels were measured in classrooms during free-time activities and in dining rooms [from 82 to 94 dB (A)]. The authors observed better acoustical conditions in new buildings, in comparison to the old ones. 
Another interesting topic of research was noise exposure of teenagers in vocational schools where they practiced some specific technical tasks, similar to industrial processes. , Investigations comprised pupils from mechanical-technical, electric-technical, construction-technical, wood-processing, textile-processing, and catering-gastronomy schools. Noise levels measured inside the school workshops ranged 80-90 dB in mechanic workshops, from 90-100 dB in textile-processing workshops, and from 92-102 dB in woodworking workshops. A control group comprised pupils who were exposed to noise levels below the recommended standards (80 dB) during technical activities in their schools.  The authors were concerned with potential hazardous effects on pupils' health, baring in mind a long exposure to noise (average duration of 4.5 h), and children's high sensitivity to noise. They proposed shortening of exposure time for pupils educated in vocational schools. 
Studies on noise measurements and exposure assessment were performed extensively in CEE, SEE, and NIS countries, predominantly in Poland and former Czechoslovakia. Researchers examined noise levels in school areas and acoustical conditions inside daycare facilities. They identified the main causes of poor acoustical environment of such facilities, including their location, construction, insulation, as well as outdoor and indoor sources of noise. Some researchers proposed measures to reduce noise levels and to prevent adverse health effects in children. However, several authors failed to describe children's general characteristics, i.e., the number of children involved in the survey, their age, gender, and socio-economic status. Other studies lacked estimation of noise exposure at home (where children spend most of the day), and during different entertaining activities. This would have given the authors an opportunity to establish a 24 h noise exposure by combining noise exposure at different settings, from a variety of sources, and of varying duration.
Effects of noise on hearing
[Table 1] presents the key studies on the effects of noise on children's hearing. In addition to assessing the acoustic conditions in schools, authors in Poland and former Czechoslovakia went one step further, trying to estimate the effects of school noise on children's hearing. Adverse acoustic conditions at schools and children's homes were related to temporary shift in auditory threshold in two large studies in Poland. , Researchers in Warsaw (Poland) observed 159 children aged 11-12 years (from primary school) and 16-17 years (from secondary schools). The children's residences and schools were divided into the noisy zone [noise levels ranging from 76 to 85 dB (A)], and the silent zone [noise levels ranging from 42 to 57 dB (A)]. The noisy zone comprised 79 children; the silent zone included 80 pupils. The authors tested the children's temporal shift of hearing threshold before and after short-term noise exposure. Children listened to an incriminating testing sound for 4 min (tone frequency 2000 Hz, intensity 80 dB (A) above hearing threshold) in a laboratory. At the beginning, the initial values of temporary shift of hearing threshold were similar between children from different acoustic zones. After listening to the testing sound, the values of temporary hearing threshold shift increased in all children. However, 2 min after switching off the sound, temporary threshold shift values were higher in children from the noisy zone, compared to children from silent zone. In other words, the hearing threshold returned to the baseline values within 2 min among children residing in a silent zone, but not among children residing in a noisy zone. The total recovery time of hearing threshold ranged from 1 to 9 min, and was significantly longer among children from the noisy zone.  The author concluded that living under noisy conditions had a negative impact on children's hearing threshold shift, described as a slower regression of changes and prolongation of time needed to return to baseline. He suspected that such a hearing impairment may manifest in all the people exposed to noise. 
A similar study was conducted on 24 primary-school pupils in Slovak Republic (former Czechoslovakia). The children's tonal hearing threshold was assessed by audiometry on four occasions, i.e., at the beginning of the 1 st lesson, at the end of the 2 nd lesson, at the beginning of the 3 rd lesson, and at the end of all lessons (4 th , 5 th or 6 th lesson, depending on the school schedule). , The testing lasted for 2 weeks. The most important finding was an increase of hearing threshold at the end of all lessons. As expected, hearing threshold at the end of the fifth lesson was higher than the hearing threshold at the end of the fourth lesson. The authors observed that the increase of hearing threshold correlated with fatigue over the course of the day. Another intriguing, yet unexpected finding was an increase of hearing threshold after the great break. This result contradicted a common belief that children would relax and revitalize during the great break, which usually follows the second lesson and lasts for 30 min. The authors explained this finding by unfavorable effects of noise coming from the streets or children's activities. They proposed that the school breaks be organized in a manner that would eliminate the impact of noise and give children possibilities for play and recreation. 
The same methodology was applied a decade later in three high schools in Bratislava (Slovak Republic, former Czechoslovakia).  The schools were selected based on their distance from the main road. The survey revealed a similar trend in changes of hearing threshold during the course of the day. However, children from quiet schools reacted with a peak of hearing threshold after the school break, which was not the case among children from noisy schools. The author concluded that the observed differences arose primarily from some social and biological factors, and not from noise exposure. 
Another large survey was performed among 301 children aged 10-12 years in two schools in Prague (Czech Republic, former Czechoslovakia). The study recruited 124 children (58 boys and 66 girls) from one noisy school (located near a highway), and 177 children (85 boys and 92 girls) from one quiet school.  The noise levels exceeded 75 dB (A) outside a noisy school, and were below 60 dB (A) outside a quiet school. The researchers tested the children's hearing and looked at their medical records. Hearing loss was diagnosed among 6.19% of the children from a noisy school, and among 1.3% of children from a quiet school. Most hearing disorders were conduction-type. According to medical records, 43.5% of children from a noisy school suffered from otitis media, compared to 28.3% of the children from a quiet school. The authors assumed that the frequent occurrence of ear diseases in children was associated with unfavorable living conditions in noisy areas.  In another study by these researchers, the same children took a tuning fork test for the distinction between perceptual and impaired hearing. As a result, 13% of pupils from the noisy school suffered from hearing loss, whereas pupils from the silent school had no auditory defects. 
Studies on the effects of noise on children's hearing were performed in former Czechoslovakia and Poland among all CEE, SEE, and NIS countries. Researchers investigated changes in the hearing threshold in a laboratory or in epidemiological surveys. They concluded that noise exposure correlated with their findings and proposed measures to reduce noise in children's environment. However, the authors failed to perform similar experimental surveys during activities outside the school setting. For example, they could have tested changes in the hearing threshold before and after noisy activities (listening to loud music, attending parties, or sport matches), as well as before and after quiet activities (play or work in silence). This would have enabled researchers to evaluate some mechanisms of hearing impairment in relation to noise exposure during the course of the day.
Effects of noise on psychological reactions and sleep disturbance
[Table 2] presents the key studies on the effects of noise on children's psychological reactions and sleep disturbance. A large survey on children's general health was conducted in Prague (Czech Republic, former Czechoslovakia) among 301 children aged 11-14 years (5 th to 7 th grade). The author observed some significant differences in the general health of children from noisy and silent schools. Children from noisy schools more often reported decreased school performance, decreased ability to concentrate, increased rate of errors, and increased feeling of irritability and fatigue.  These findings were more prominent in "neurotic" children who appeared to be particularly sensitive to the quality of their school environment. However, the paper does not provide any explanation how neurotic children were identified. This word describes excessive anxiety and emotional distress, but is no longer used scientifically. The author concluded that noise exposure was a markedly unfavorable factor for the healthy development of children. 
Some experimental and field studies reported that noise induced stressful reactions in schoolchildren. For example, children exposed to noise over 75 dB (A) in schools in Russia (former USSR) complained of their inability to relax in noisy conditions.  Children from noisy schools in Poland reported hearing deficiencies and psychic disturbances more often than did children in quiet schools.  The authors, nevertheless, failed to report the exact noise levels the children were exposed to; they separated the schools according to the accepted outdoor noise limits. The study also lacks a description of psychic disturbances and their assessment. In another study, the authors selected two schools in Prague (Czech Republic, former Czechoslovakia); a noisy school was located near a high-way (measured equivalent noise levels exceeded 75 dB (A) outdoors), and a quiet school was located far away (equivalent noise level was around 65 dB (A) outdoors). The parents whose children attended a noisy school more frequently reported that their children suffered from irritation, fatigue, exhaustion, and inability to concentrate.  At the same time, 'neurotic' children from a noisy school showed poorer overall performance than did neurotic children from a quiet school. Again, the word neurotic was not defined in the paper. The authors concluded that these psychological reactions were related to long-term exposure to noise.  In one experimental study, children from noisy and quiet residential areas were exposed to noise-testing. Children from noisy areas were more stressed by noise in the laboratory and less resistant to its impact. The authors suspected that these effects contributed to children's poor school performance. 
Another measure for task performance or attention is the auditory reaction time. Researchers in Bratislava (Slovak Republic, former Czechoslovakia) tested the hypothesis that background noise may slow reaction time among high-school children.  The study enrolled 200 children from a noisy school and 200 children from a quiet school. Noise measurements inside the classrooms determined whether the schools were noisy or quiet. The children's age was not specified in the paper, but it was probably around 15 years (secondary school). Researchers measured the pupils' reaction time to sound stimulus that lasted for 5-6 min. The test sound had a frequency of 1000 Hz, intensity of 60 dB (weak tone) or 80 dB (strong tone). In a quiet school, the children's reaction time increased at the beginning of the third class (after a 30 min school break), but decreased steadily at the end of all classes. However, in a noisy school, the children's reaction time increased during the course of the classes when they listened to a strong tone, but decreased when they listened to a weak tone. The author explained that this was a result of the inadequate location of a noisy school, poor ventilation of the classrooms, and long-term work distress of children. 
Sleep disturbances in children were not much explored in CEE, SEE, and NIS countries, except for the two studies from Poland and former Czechoslovakia that looked into the effects of noise on the afternoon sleep of children in nursery schools. In total, researchers followed more than 2500 preschool children while sleeping after lunch under different acoustic conditions. Under noisy conditions, children needed more time to fall asleep, slept less, moved their bodies more often, , woke more often, and had difficulties in falling asleep again.  The most prominent effects were observed in nurseries with outdoor noise levels above 65 dB (A). Researchers proposed that daycare facilities should not be constructed in areas where noise levels exceeded 60 dB (A). 
An interesting study in former Czechoslovakia explored the effects of noise on the control of upright posture of schoolchildren.  A group of 36 boys aged 11-12 years listened to tape-recorded school noise of 85 dB (A) for 45 min. Concurrently, pupils fulfilled a mental performance test, intended to maintain their vigilance level. A control group included 24 boys who completed the same test, but were not exposed to noise. The outcome of the study was the number of body sways (movements of the upper body in sagittal plane), which was recorded before noise exposure, 5 min after the onset of noise, and finally after the cessation of noise. The experimental group reacted differently from the control group. Immediately after the onset of noise, the number of body sways decreased. After 45 min of listening to the test sound, the number of small-amplitude body sways decreased, but the number of large-amplitude body sways increased. On the other side, the number of body sways among control pupils decreased steadily during the test. The same experiment was repeated 2 weeks later, i.e., all children completed the mental task, but only experimental group listened to the testing noise. The exposed children reacted with an increase of the total number of body sways in all amplitude zones.  The authors concluded that repeated mental tasks without noise exposure diminished the number of body sways, whereas mental tasks in the presence of noise resulted in an increase of the number of body sways. They suggested that children affected by noise had worse maintenance of body posture, but acknowledged their inability to separate the effects of noise and mental task. 
Two researchers from Bratislava (Slovak Republic, former Czechoslovakia) tested the children's auditory reaction time in two experimental situations. In the 1 st experiment, 72 fourth-grade schoolchildren (approximate age 10-11 years) completed some psychological tests (two performance tests, a test of learning process, and a test of motor coordination) that imitated working conditions during an average class. One group of children was exposed to noise of 65-85 dB (A), whereas the other group worked in silent conditions.  As a result, noise exposure did not affect the children's reaction times and their performance at performance testing, even at the highest noise levels.  In the second experiment, 24 fourth-grade schoolchildren completed the same performance-oriented tests.  One group of children worked in silent conditions at 1 st , and was exposed to noise later [noise level of about 85 dB (A)]. The other group was at first exposed to noise, and worked in silence later. The first group of children (who worked in silence first and listened to noise later) performed significantly better in all applied tests, but had similar reaction time compared to the second group. The authors concluded that the experiment demonstrated a disturbing effect of noise on the children's ability to acquire knowledge and to gather psychical reserves in the process of learning. 
Studies on the effects of noise on children's health were conducted in experimental and fieldwork settings predominantly in former Czechoslovakia and Poland, among the CEE, SEE, and NIS countries. The authors investigated several aspects of children's health, such as psychological reactions, school performance, reaction time, afternoon sleep and upright posture. However, other adverse effects of noise remained unexplored, including noise annoyance, disturbances of nighttime sleep, and cognitive impairments (attention, memory, reading or writing comprehension). Although researchers proposed measures to reduce noise exposure in school settings, they may be criticized for not performing intervention studies that would have helped them explore the changes in various aspects of children's health after the implementation of noise-abatement programs at schools and other daycare facilities.
Effects of noise on vegetative functions and blood pressure
[Table 3] presents the key studies on the effects of noise on vegetative functions and blood pressure of children. A team of researchers in former Czechoslovakia performed extensive experimental research in this field. ,, The first study comprised ten primary schools in Bratislava (Slovak Republic, former Czechoslovakia).  It included 72 fourth-grade schoolchildren (approximate age 10-11 years). The children had their skin reactivity measured at palmar region. The children also completed some psychological and mathematical tests that imitated working conditions during an average class. One group of children was exposed to noise of 65-85 dB (A), whereas the other group worked in silent conditions. As a result, the bioelectric reactivity of the skin decreased in children from both groups during the experiment. Bioelectric reactivity of the skin decreased sharply in the children exposed to noise, but showed greater individual variations than in the control group. The authors indicated that the children exposed to noise had more difficulties adapting to noise than did children who worked in silence. 
In another study, 24 children (aged 10-11 years) listened to a tape-recorded school noise of 85 dB, while fulfilling a psychological test at the same time.  The authors found statistically significant effect of the general load (both noise and psychological tests) on children's bioelectric reactivity of the skin and their heart rate. The authors concluded that the bioelectric reactivity of the skin proved to be a more sensitive indicator of the children's vegetative functions than heart rate. They acknowledged their inability to separate the effect of noise from the effect of testing conditions on children. They explained this by too high "neuropsychic load" of the selected mental tests that superimposed the effect of noise.  Later, the same researchers performed a similar study on children, giving them attention tests in two experimental settings, while measuring their heart rate.  As previously described, one group of children worked in silent conditions at first, and was exposed to noise later [noise level of about 85 dB (A)]. The other group was at first exposed to noise, and worked in silence later. Although their performance results were different, children from both groups had similar heart rates during the testing. 
Russian researchers were pioneers in the research of the effects of noise on blood pressure in children.  They were the first to investigate the effects of aircraft noise on populations living in 22 urban and rural settlements around nine civil airports. Schoolchildren (9-13 years old, number not specified) were examined in clinical departments at their place of living. Investigators showed that the children residing in settlements within 6 km from the airports had blood pressure abnormalities, higher liability of pulse, local and general autonomic vascular changes, and cardiac insufficiency. In addition, the investigators reported that children suffered from increased fatigue and that they had reduced auditory capacity for low and high sonic frequencies.  They proposed permissible aircraft noise levels in urban areas - [85 dB (A) at daytime, 75 dB (A) at night time], and some technical and administrative measures for the reduction of noise levels near airports.  However, the methodology of this study is questionable, because it provides no information on noise measurements, selection of participants, or comparisons with a control population living faraway from the airport. Furthermore, this study lacks details on the clinical examination of children, i.e., cardiovascular measurements (blood pressure, heart rate, other cardiovascular indices), hearing assessment (the term "auditory capacity" was not defined in the paper), and control for basic covariates (age, gender, weight, and height). Such crucial limitations make this otherwise famous survey difficult to compare with modern studies on the same topic.
Later on, researchers in Poland examined reactions of the circulatory system (systolic and diastolic pressure and heart rate) among children exposed to laboratory noise.  Elementary and secondary schoolchildren were divided into two groups according to noise levels at their residences. Children from the noisy zone resided in areas with noise levels between 76 and 85 dB (A); children from the silent zone were living in areas with noise levels ranging from 42 to 57 dB (A). The experiment involved a 4-min exposure to a single sound (frequency of 2000 Hz, levels of 80 dB (A)over hearing threshold). It resulted in a significant increase of diastolic blood pressure and heart rate, a decrease of pulse amplitude and an insignificant increase of systolic blood pressure among all children.  However, children from the noisy zone reacted slightly differently than did children from the silent zone. For example, systolic blood pressure and heart rate increased steadily in all the children during noise exposure. At the end of noise exposure, both parameters remained high in children from the silent zone, but suddenly dropped among children from the noisy zone. As for diastolic blood pressure, it dropped at the beginning of noise exposure, but increased during the testing in children from the silent zone. In children from the noisy zone, the diastolic blood pressure changed in a completely reversed order, but the differences were statistically insignificant. Another important finding was that younger children responded to laboratory sound more markedly than did adolescents. The researcher assumed that long-term exposure to noise at home must have modified the adolescents' cardiovascular response to sound emitted in the laboratory. 
The largest study comprised more than 1500 children from kindergartens in Slovak Republic.  Researchers performed noise measurements and noise mapping on various locations around the city, and matched kindergartens and residences with equivalent noise levels. Children's homes and kindergartens were defined as quiet [noise level below 60 dB (A)], noisy [noise levels from 61 to 69 dB (A)], and very noisy [noise levels exceeding 70 dB (A)]. Researchers measured the children's blood pressure by a sphygmomanometer for 2 or 3 times, and their heart rate in between. Children attending noisy and very noisy kindergartens had 4-5 mmHg higher systolic and diastolic blood pressure than did children attending quiet kindergartens. Noise at homes had smaller, but significant impact on the children's blood pressure. Children residing in noisy and very noisy homes had 1-2 mmHg higher systolic and diastolic pressure, compared to children from quiet homes.  An opposite association was observed between noise exposure and heart rate; i.e., children from noisy and very noisy kindergartens and residences had lower heart rate than did children from quiet areas. The effect of noise on blood pressure remained significant after adjustment for children's age, body weight, and height. This was also the first study to report the association between noise exposure and blood-pressure percentiles. The incidence of children with blood pressure values above the 95 th percentile (systolic blood pressure above 120 mmHg; or diastolic blood pressure above 75 mmHg) was the highest in noisy and very noisy kindergartens.  The authors proposed some physiological explanations for the increase of blood pressure and decrease of heart rate in relation to noise exposure, but refrained from claiming that the association was causal. This study may be criticized for its methodology, i.e., for measuring blood pressure at school (not at home), on a single occasion (instead of on several occasions), and for not performing 24 h readings. On the other side, high costs of 24 h blood pressure measurements would have prevailed over its benefits and would have caused lower response rate and greater resistance of children and their parents toward research.
Studies on the effects of noise on children's vegetative functions and blood pressure were widely performed across CEE, SEE, and NIS countries, primarily in former Czechoslovakia, Poland, and former USSR. Their results contributed to understanding the relationship between noise exposure and children's vegetative reactions. Some studies must be criticized for failing to separate the effect of noise from the effect of other tasks (mental performance tests), and for not controlling the other factors affecting children's vegetative functions (fear, anger, anxiety of the examination, noise sensitivity, children's health, etc.). Finally, the cross-sectional design of such studies did not allow researchers to predict changes of vegetative functions and blood pressure of children after long-term exposure to noise. Future follow-up studies should provide more insight to the nature of the relationship between noise and children's cardiovascular system, and examine individual differences between children from different countries across Europe.
Effects of noise on newborns
One of the most significant research topics in CEE, SEE, and NIS countries included the effects of noise in incubators on newborns. Researchers from Poland and former Czechoslovakia were the first to measure noise levels inside incubators. , In Poland, noise levels were measured in two models of incubators, and the average noise level was 60 dB (A). In addition, researchers measured vibrations in two positions, at the infant's head, and at the infants' feet. Average vibration levels were 0.065 m/sec 2 (A-weighted) at head position, and 0.105 m/sec 2 (A-weighted) at feet position.  In Slovakia (former Czechoslovakia), researchers measured noise levels in 72 incubators (four models) under different operational conditions. Noise levels ranged from 51.6 to 61.7 dB (A) (64.2-79.7 dB). Noise levels inside the incubator were 15 dB (A) higher with an infant inside, compared to empty incubators. The highest noise levels were recorded during opening and closing the doors of the incubators, and during inconsiderate contacts of the nursing staff with the incubator walls. 
As for harmful effects of long-term exposure, researchers from Poland suspected that noise and vibrations in incubators lead to some metabolic, cardiovascular, endocrine, and auditory changes.  Almost a decade later, researchers from Slovakia performed an experimental study on 30 newborns in the incubators.  The children's birth weight was 1613 ± 412 g; actual weight was 1861 ± 245 g; their age was 30 ± 17 days. Newborns were exposed to low-frequency noise (frequency between 63 and 250 Hz), which is typically generated by closing the doors of the incubator. Noise stimulus was applied repeatedly for 5 min within a time interval of 30 s. On another occasion (not specified in the paper), children were exposed to high-frequency noise (frequency around 4000 Hz) which is typically generated by the incubator alarm. This noise exposure lasted for 30 s as well. Babies were sleeping during the experiments and measurements. Their blood pressure and heart rate were recorded before noise stimulus (pre-exposure levels), immediately after the emission of a stimulus, and every minute afterwards, until blood pressure returned to the pre-exposure levels.  The main outcome of the study was an increase of all parameters after noise stimulus. Systolic and diastolic blood pressures (measured by ultrasound) increased by 10 ± 4 mmHg and by 9 ± 4 mmHg (respectively). The size of the effect was similar for low-frequency noise and high-frequency noise. Heart rate (measured by electrocardiography) increased by 28 ± 13 beats per minute after exposure to low-frequency noise; and by 30 ± 10 beats per minute after exposure to high-frequency noise. However, this effect was not evident in all the children; a decrease in all investigated indices was observed in about 15% of newborns. Both blood pressure and heart rate returned to pre-exposure values within 4-5 min. The authors concluded that noise stimuli, regardless of frequency, intensity and duration, lead to substantial somatic responses. They proposed noise inside the incubators an important perinatal risk factor for possible vegetative disturbances. 
Studies on the effects of noise on newborns in incubators performed in Poland and former Czechoslovakia were among the rarest in CEE, SEE, and NIS countries. The researchers failed to examine the effects of noise on newborns' hearing, did not control for the length of stay inside the incubator, for the concurrent use of medications (especially ototoxic antibiotics), and did not take into account infants' health (newborns with congenital diseases or malformations versus healthy newborns with low-birth weight). Recent reviews indicate that loud incubator noise has negative short-term effects on the cardiovascular and respiratory systems of preterm infants.  Future studies should address the long-term effects of incubator noise and provide some explanation for the association between noise and neonatal pathology.
| Conclusions|| |
Research on the effects of noise on children's health was conducted in many CEE, SEE, and NIS countries between 1965 and 2000 in both experimental and field settings. Some studies focused on measuring the noise levels outside daycare facilities and on the assessment of indoor acoustical conditions. Others documented the effects of noise on children's health, such as hearing, psychological reactions, sleep disturbances, performance. Researchers from CEE, SEE, and NIS were the pioneers in the assessment of noise-induced changes in vegetative functions and blood pressure of children in urban settings. They also initiated research on the effects of incubator noise on vegetative functions of infants.
This review shows that good ideas exist in all parts of the world. Despite some inconsistencies in their methodology, these surveys achieved in making significant impact on the understanding of the role of noise in the environment and its impact on humans. Young researchers would benefit from the amount of knowledge built up in the reviewed studies. Scientists are encouraged to re-read these early articles, find inspiration in their methodology, pursue their original ideas, and improve them in the subsequent noise research.
| Acknowledgments|| |
I specially thank my colleague Dr. Lubica Argalasova-Sobotova (Institute of Hygiene, Faculty of Medicine, Comenius University, Bratislava, Slovak Republic), who inspired me with the idea and supported me in completing this study. I am grateful to
Dr. Wieslaw Sulkowski (Nofer Institute of Occupational Medicine, Lodz, Poland), Dr. Mariola Sliwinska-Kowalska (Nofer Institute of Occupational Medicine, Lodz, Poland), and Sonja Jeram (Institute of Public Health, Ljubljana, Slovenia), who helped me obtain some original papers published in National Journals. This research received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement No 226442, and from the Ministry of Education and Science of Serbia, Project No. 175078.
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Institute of Hygiene and Medical Ecology, Faculty of Medicine, University of Belgrade, Dr. Subotica 8, 11000 Belgrade
[Table 1], [Table 2], [Table 3]