**7. Effect of noise stress on autonomic nervous system**

Unlike note, noise is produced when sound waves are emitted from multiple sources. Noise has been reported to impact autonomic nervous activity. Goyal *et al*., [42] exposed 200 adult males to noise intensity of greater than 80 dB for about 6 months. Noise exposure increased heart rate and systolic blood pressure. Idrobo-Ávila *et al*., [43] in their systematic review noted that noise exposure increased heart rate and blood pressure and caused alteration in both high frequency and low frequency/high-frequency ratio. Chen *et al*., [44] examined the connection between occupational exposure to noise and high blood pressure using 1390 workers exposed to occupational noise. The authors reported that noise exposure caused an increase in systolic blood pressure and diastolic blood pressure. According to the study, the prevalence of high blood pressure was found as 17.8% in those who were exposed to noise and 9% in those who were not exposed to noise. Hey also claimed that there existed a stronger regression coefficient between diastolic blood pressure and noise exposure. Noise intensity, cumulative noise exposure, and years of exposure were related to high blood pressure risk. de Souza *et al*., [45] claimed that exposure to noise was associated independently with high blood pressure at 75–85 dB. The study recruited 1729 subjects who were petrochemical workers. The authors also found that age, body mass index, and gender were associated with high blood pressure independently. A study by Brahem *et al*., [46] was conducted on 120 electricity workers who were exposed to noise. Prevalence of high blood pressure was found in workers who were exposed to noise. Systolic blood pressure and diastolic blood pressure were higher in workers who were exposed to noise. Kuang *et al*., [47] showed that increasing years of exposure to occupational noise increased systolic blood pressure and diastolic blood pressure.
