ارتباط بین عوامل ارگونومیک خطر صوت و علائم صوتی، معلولیت صوت، و بیماری های تنفسی

Objectives The aim of the study was to investigate the connections between voice ergonomic risk factors found in classrooms and voice-related problems in teachers. Methods Voice ergonomic assessment was performed in 39 classrooms in 14 elementary schools by means of a Voice Ergonomic Assessment in Work Environment—Handbook and Checklist. The voice ergonomic risk factors assessed included working culture, noise, indoor air quality, working posture, stress, and access to a sound amplifier. Teachers from the above-mentioned classrooms reported their voice symptoms, respiratory tract diseases, and completed a Voice Handicap Index (VHI). Results The more voice ergonomic risk factors found in the classroom the higher were the teachers' total scores on voice symptoms and VHI. Stress was the factor that correlated most strongly with voice symptoms. Poor indoor air quality increased the occurrence of laryngitis. Conclusions Voice ergonomics were poor in the classrooms studied and voice ergonomic risk factors affected the voice. It is important to convey information on voice ergonomics to education administrators and those responsible for school planning and taking care of school buildings.

The causes of dysphonia are more often environmental (65%) than genetic (35%).1 Thus, it is not surprising that teachers are known to suffer from voice disorders more often than workers in other occupations.2, 3, 4 and 5 In spite of this, virtually no remedial measures have been taken—either for voice ergonomics in schools and classrooms or on the level of society and legislation.6 and 7 The risk factors for voice disorders are quite well documented. One of the most obvious is related to working culture, namely the excess of voice use. Indeed, teachers' phonation time at work has been found to be longer (20–40% of working hours8, 9, 10, 11 and 12) than in other professions (under 10% of working hours8, 10 and 13). Some teachers, like music teachers, use their voices even more than those teaching other subjects.14 In addition to long talking times, teachers' voice levels may be high.10, 12 and 15 One reason for raising the voice level is long speaking distance. Another reason is background noise: people raise their voices in a noisy environment because of the Lombard effect.16, 17 and 18 Loud background noise levels have frequently been measured in schools and kindergartens.10, 19, 20 and 21 Much noise originates from classroom activities, and the noisiest of these have been measured to be 20 dB louder than the quietest working.20 Urban schools may also suffer from noise outside the buildings; for instance, 86% of the schools in London were exposed to an average traffic noise level of 57 dB LAeq.20 Poor acoustics increase the harmful effects of noise by making the noise continuous and restricting the noise attenuation.10, 19 and 22 Furthermore, the speech transmission index, which expresses speech transmission in a space, has been found to be poor in classrooms19 and kindergartens.10 Teachers with voice problems are reportedly more prone to suffer from acoustic defects than teachers without them.23 The voice is also affected by indoor air quality, which has been shown to be poor in many European schools.24 Exposure to organic dust may cause voice symptoms,25 and organic and chemical impurities trigger allergic or inflammatory reactions in the laryngeal mucous membranes.26 and 27 Respiratory allergies, in turn, increase the risk for voice symptoms.28 Moreover, the risks will multiply if ventilation is poor, as has been reported to be in many classrooms.29 Water damage is one source of poor indoor air, increasing the risk of mold formation. A study conducted in 12 countries reported visible mold in 13.9–39.1% in buildings.30 Mold emits toxic substances that may cause voice problems31 and 32 and upper respiratory symptoms.31, 33 and 34 Humidity and temperature are also factors affecting indoor air quality. In a cold climate, the indoor air may be very dry, and the moisture-retaining capacity of the air decreases rapidly as the temperature of the air falls.35 Low relative humidity affects voice production. It stiffens the cover of vocal folds and increases the viscosity of mucosa,36 which, in turn, changes the mucosal wave by decreasing its amplitude and frequency.37 and 38 As a result, the phonation threshold pressure increases.39, 40, 41 and 42 Some voice ergonomic risk factors, like working posture and emotions, are related to the speaker. Good postural alignment is important in optimizing voice function.43 Patients with voice disorders have been found to have musculoskeletal abnormalities connected to the voice production structures, such as a high-held larynx, contraction of the stylohyoid and sternocleidomastoid muscles, and a weak deep flexor mechanism.44 Of the working postures, sitting and standing have been shown to affect voice production differently.45 Emotions have a strong connection to the voice production.46 and 47 Stress and anxiety change the acoustic features of the voice48 and have been found to be associated with voice symptoms in teachers49 and 50 and student teachers.51 Teaching indeed includes numerous stressful factors. Most of the stressing teachers are maintaining discipline, time pressures, and workload.52 In addition, personal traits may affect how people react to situations. Teachers with functional dysphonia may have temperamental features that elevate their reactivity to stress,53 and 54 the level of which may increase to the same intensity as in the people with social anxiety.55 Voice disorder as an occupational hazard was reported as early as in the 1950s according to our search of Medline. During the last decade especially, extensive surveys of risks for voice use related to environmental factors10, 23, 49, 56 and 57 and studies dealing with workload changes in teachers' voices58 and 59 were carried out. Thanks to these and other studies on teachers' voices, the understanding of the voice problems caused by the teaching environment has increased. However, to the best of our knowledge, a systematic voice ergonomic assessment protocol for measuring and inspecting risk factors in a working place has been lacking. The Voice Ergonomic Assessment in Work Environment—Handbook and Checklist (VEAW; in Finnish and Swedish) created by Sala et al60 is such a tool. The publication was originally intended for the clinical use of occupational health care experts, but it can also be used in research. This study is a part of a larger voice ergonomic research project on elementary schools. The aim of the present study was to assess voice ergonomic risk factors and their connections with teachers' voice symptoms in a real teaching environment by means of the VEAW. In addition, we studied if the teachers suffering from respiratory tract diseases had poorer indoor air quality in their classrooms than those without these diseases. The research also serves as a validating process of the VEAW.

Voice ergonomics were poor in the classrooms studied and voice ergonomic risk factors affected the voice. It is important to convey information on voice ergonomics to education administrators and those responsible for school planning and taking care of school buildings.