Introduction
The humans are extensively affected by noise, ranging from slight annoyance to hearing loss.1 The direct health-related effects of noise on humans are hearing impairment, speech disturbance, performance issues, mental problems, sleep disturbance, and annoyance, while indirect health-related effects are dysfunction of the autonomic nervous system (ANS) and cardiovascular system.2
Materials and Methods
50 young male volunteers were taken in this study and were randomly divided into two groups and they were exposed to two different types of white, traffic noise. We also measured HRV parameters before and after exposure to noise.3,4,5,6 The HRV parameters were evaluated and frequency domain analysis were then perform ed with the help of RMS polyrite – D version 3.0.11.
Statistical analysis
Descriptive statistical analysis has been carried out in the present study. Results on continuous measurements are presented on Mean SD (Min-Max) and results on categorical measurements are presented in Number (%). Significance is assessed at 5% level of significance. Analysis of variance (ANOVA) has been used to find the significance of study parameters between three or more groups of patients, Student t test (two tailed, independent) has been used to find the significance of study parameters on continuous scale between two groups Inter group analysis.7
Results
Our study shows that there is increased sympathetic activity and decreased parasympathetic activity due to traffic noise in humans. HF nu is significantly decrease in traffic noise when compared to white noise with p<0.05, and a significant(p<0.05)increase in LF nu and LF-HF ratio is significantly increased when compared to white noise.
Table 1
| Variables | Subjects |
| Age in years | 20±2 |
| BMI (kg/m2) | 23.06±0.31 |
Basic characteristics of subjects
Table 2
Comparision of FFT spectrum between white noise and traffic noise
Discussion
It is generally accepted that noise exposure enhances sympathetic nerve activity. Although investigators have sought to measure stress responses to acute noise exposure, the currently used objective parameters include stress hormone levels and HRV. Measuring of pulse rate and BP changes are well established methods for measuring overall cardiovascular responses. However, these methods can exhibit immediate reactions upon exposure to strong noise, and it is difficult to identify such changes in response to weak or moderate noise. Therefore, recent studies have investigated variables associated with ANS activity.1
In a study by Lee, et al., which compared HRV according to noise loudness, no noise-related differences in HF, an indicator of parasympathetic nervous system activity, were observed when the same subjects were presented with white noise at levels of 23, 50, 60, 70, and 80 dB(A).4
However, significant increases were observed in LF and the LF/HF ratio as the noise level increased. This finding was interpreted as demonstrating increased sympathetic nervous system activity simultaneously with the increased acute noise level.8
Among studies that observed changes in heart rate according to noise type, Umemura and Honda measured changes in subjects heart rates after listening to classical music, rock music, and noise.9
Among subjects who listened to classical music, LF (an indicator of sympathetic nervous system activity) decreased during the stable stage, whereas among subjects who listened to rock music or noise, LF increased. This indicated that the sympathetic nervous system was inhibited in subjects who listened to classical music, yet excited in subjects who listened to rock music or noise. It can also be inferred that classical music would promote comfort, whereas rock music or noise would induce discomfort or tension. Therefore, it could be suggested that even noises of the same intensity may have different impacts on the ANS, depending on the type of noise.
In this study there was a significant (p<0.05) decrease in HF nu in traffic noise when compared to white noise, and a significant (p<0.05) increase in LF nu and LF-HF ratio in traffic noise when compared to white noise. Thus indicating increased sympathetic activity and reduced parasympathetic activity in traffic noise. These results are in accordance with those of previous studies, which showed that classical music increased comfort and decreased the LF level.
Limitations of the study
The present study is focused only at the effect of noise stimuli on the cardiac autonomic frequency domain parameters. The study is limited to one geographical area and confined to one gender of a specific age group.
Conclusion
These results suggest that with appropriate noise exposure levels, we could observe activated ANS function and an improved degree of overall balance between the sympathetic and parasympathetic nervous systems. Typically, the theory of traffic noise acting as a stressor and exerting a negative impact on the human body has been dominant. According to the results obtained in this study, white noise might act as a eustressor that relieves anxiety resulting from silence. Additionally, these results suggest that an appropriate noise level can positively affect the ANS.
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