Night-Time Noise Index Based on the Integration of Awakening Potential

Calculation of the physiologically developed nighttime noise index from existing noise indices

Background:

The effects of noise on sleep and health have been evaluated in earlier studies using noise indices chosen on the basis of practical considerations and not on the physiologic mechanisms of sleep disturbance due to noise exposure. We investigated the neurophysiologic mechanisms of sleep and found that the arithmetic mean of the sound levels above a threshold () may be used effectively to evaluate the effects of nighttime noise exposure. However, the efficacy of using has only been confirmed in a specific setting; therefore, the reliability of in other situations should be investigated by applying it in epidemiologic studies. In this study, we aimed to obtain an alternative equation for calculating from existing noise indices, given that detailed information on fluctuations in sound levels, needed to calculate according to the definition, is not readily available.

Materials and Methods:

We examined statistical relationships among noise indices namely , the number of noise events above 60 and 70 dB (N₆₀ and N₇₀), and the night equivalent sound level (L_night). The study area was around the Kadena military airfield, where the sound levels were recorded at noise monitoring stations.

Results:

showed a very strong correlation with N₆₀ and N₇₀ but not with L_night. Among regression equations, an equation representing N₆₀ and the interaction between N₆₀ and L_night, which is equivalent to the product of N₆₀ and a linear expression of L_night, showed the highest prediction capability.

Conclusion:

We obtained a regression equation to calculate from N₆₀ and L_night. Although this alternative equation for is only applicable for military aircraft noise, it will aid the re-analysis of existing epidemiologic studies as well as further investigations on the relationship between noise exposure and health effects.

Development of a new night-time noise index: Integration of neurophysiological theory and epidemiological findings

Background:

The effects of environmental noise on sleep are of great interest to public health. Numerous studies have been conducted to investigate these effects; however, these previous studies applied existing sound-level statistics that were not based on neurophysiology.

Aims:

This study aimed to develop a new night-time noise index based on neurophysiology and epidemiology.

Methods:

First, we derived a formula for predicting the noise effects on sleep based on a neurophysiological model of brainstem sleep regulation, where awakening was associated with greater electrical potentials in the brainstem. Second, we investigated the noise effects on sleep using the results of an epidemiological study conducted in the vicinity of the Kadena military airfield in Okinawa, Japan. Thirty volunteers participated in the study. Vibrations of whole-body movements were recorded using sheet-shaped sleep monitors for 26 consecutive nights. The onset of motility, which was defined by monitor vibrations, was used to index awakening reactions.

Results:

Our statistical model could properly predict the fluctuating risk of motility onset. The new index, which is the mean of the sound level above 60 dB, can be successfully used, irrespective of the duration of noise exposure. Additionally, it out-performed existing event-related noise indices.

Conclusions:

We derived a new night-time noise index for evaluating the noise effects on sleep. To our knowledge, this is the first study to explain the noise effects on sleep with the consideration of neurophysiology and epidemiology.

A Neurophysiological Approach for Evaluating Noise-Induced Sleep Disturbance: Calculating the Time Constant of the Dynamic Characteristics in the Brainstem

Chronic sleep disturbance induced by traffic noise is considered to cause environmental sleep disorder, which increases the risk of cardiovascular disease, stroke, diabetes and other stress-related diseases. However, noise indices for the evaluation of sleep disturbance are not based on the neurophysiological process of awakening regulated by the brainstem. In this study, through the neurophysiological approach, we attempted (1) to investigate the thresholds of awakening due to external stimuli in the brainstem; (2) to evaluate the dynamic characteristics in the brainstem and (3) to verify the validity of existing noise indices. Using the mathematical Phillips-Robinson model, we obtained thresholds of awakening in the brainstem for different durations of external stimuli. The analysis revealed that the brainstem seemed insensitive to short stimuli and that the response to external stimuli in the brainstem could be approximated by a first-order lag system with a time constant of 10-100 s. These results suggest that the brainstem did not integrate sound energy as external stimuli, but neuroelectrical signals from auditory nerve. To understand the awakening risk accumulated in the brainstem, we introduced a new concept of "awakening potential" instead of sound energy.