Assessment of Hearing Impairment and Hypertension among workers exposed to occupational noise in Baiji power plants

Abstract

Methods: This was a cross-sectional study. The study sample (population)   consisted of 240 healthy male employees from  Baiji electric power plants with a history of past and present exposure to noise. The study was conducted during the period from the 15 December of 2012`to the 15 February of 2013. There are four sections in the power plants. Turbine, Boiler, central control room and fuel . All workers who worked in the power stations for 5-7 years or more were included in the study. Data was gathered from the results of available portable audiometric test and the blood pressure was measured in supine position by using mercury sphygmomanometer 
Hearing impairment was defined as average hearing threshold  for frequencies 0.5kHz, 1kHz ,2kHz and 3kHz equal or more than 25 dB(A) in  both ears. Workers are classified according to exposure time in to two groups. The workers are working in turbine and boiler formed continuously exposed group(CEG).While the workers are working incentral control room and fuel formed intermittently exposed group(IEG). 
Results:The prevalence of hearing impairment in this study was 17.08% among all the exposed workers. The prevalence of hearing impairment was significantly more in(CEG 14.58%)as compared to  (IEG  2.5%).The  Prevalence  of  hypertension  among  continuous  exposure  group  to  noise was(12.5%) significantly higher than the  intermittent exposed group  to noise ( 2.08%) .There was a positive association between duration of exposure and prevalence of Hypertension. Both hearing impairment and hypertension showed in the current study increasing frequency in relation to the duration of exposure( employment). 26.6% of hearing impairment cases found among those exposed for less than 15 years while 72.7% among those exposed for 15 years and more .On the other hand, hypertensive were 28% and 45.6% respectively with period of duration of exposure. The results of the present  study  indicate  that    hypertension  and  hearing  impairment  are  commoner  in  workers continuously  exposed  more  than  that  in  workers  intermittent  exposed  group  to  high  level  of occupational noise. The prevalence of hearing impairment and hypertension distributed according to the age of workers, we found that the 12.95%  of bilateral neurosensory in age below 40 years, while 30.04% of cases in age above 40 years.While the prevalence of hypertension,  we found 10.47% of cases in age below 40 years and 30.6% in  age above 40 years .The most common group affected by hearing impairment (permanent bilateral) were present in Turbine and boiler of power plants. The common age group affected is above 40 year old. 
The study shows that the longer  exposure to noise either during the working day or through the period of employment increased the chance to developing hearing impairment and hypertension. The occupational hearing loss due to work related disease are common and constitute up to(14%) of all occupational hearing diseases. 
Conclusions: These findings provide corroborative evidence to further substantiate the notion that exposure to noise is associated with hearing impairment .They also support the proposition that long term occupational exposure to noise appears to be a risk factor for arterial hypertension.