Tuesday, October 21, 2014

Infant Sleep Machines and Hazardous Sound Pressure Levels

Hugh, S., Wolter N., Propst, E., Gordon, K., Cushing, S., Papsin B. Infant Sleep Machines and Hazardous Sound Pressure Levels, Pediatrics, 2014, Volume 133, Number 4.


In this paper the authors aimed to quantifying the maximum output levels of 14 different models of infant sleep machines (ISMs) commercially available in the United States and Canada. The study was initially motivated by health concerns, since the consistent use of these devices, which produce ambient noise or noise, can possibly induce hearing loss in babies, especially when used at high output levels.

Methodology consisted of measuring ISMs´ sound levels at 3 distances (30 cm, 100 cm and 200 cm) using a sound level meter in a sound booth. Both ISMs and sound level meter were placed in tables of equal height, and the sound level meter microphone was fit a 2 mL coupler in order to simulate the human external auditory canal, and to assure that measurements were considered where the tympanic membrane would be in humans. Each machine was turned up to maximum volume, and 3 trials of 30 seconds were performed for each sound. Correction factors were made for the differences in resonant properties between the 2 mL coupler and the infant´s ear canal.

Results indicated that “for all sounds, effective output level decreased with increasing distance”. The mean maximum effective output levels at 30, 100 and 200 cm were 79.1 decibels (dBA), 70.5 dBA and 63.3 dBA, respectively. Three ISMs were capable of producing noise higher than 85 dBA at a distance of 30 cm. Furthermore, all 14 ISMs were capable of producing noise higher than 50 dBA at distances of 30 and 100 cm.

As a conclusion, researchers addressed the need to monitor and limit the exposure of infants to ISM devices, which may place them at risk of developing noise-induced hearing loss or imperfect development of the auditory system.  Authors highlighted that infant specific noise exposure guidelines for hospital nurseries and neonatal intensive care units are limited to 50 dBA measured over 1 hour. In the present study results showed that at 30 cm and 100 cm distance, the maximum output of all ISMs exceed the recommended limits. Nevertheless, authors also stated that ISMs can be used safely with policy recommendations for both manufacturers and families. Therefore, it is suggested to “place the ISMs as far away as possible from the infant and never in the crib, play it at low volume and for a short duration of time”.

As a child psychiatrist I enjoyed reading this paper since the topic is relevant for infant´s health: sleep.

In the introduction, Papsin and his colleagues described for what purpose infant sleep machines have been designed for (such as to provide ambient noise and to prevent arousal from sleep by masking disturbance environmental sounds). However, to my opinion they failed to explain the difference between noise and white noise, and how noise is perceived by the infant´s brain.  Nonetheless, the authors mentioned the potential deleterious effect of noise on the physiologic state and hearing of infants, which can influence both the quality and quantity of sleep.

One of the drawbacks of this study is that it was not performed in infants. This is understandable, as the time span required to design, execute a cohort study for infants and disseminate results would take long, whereas the main concern of authors were to warn scientific community and society about the risk of these devices and to recommend a quick and safer use. I consider that the future studies to be performed in children exposed to ISMs noise should control the proximity to ISMs, type of noise, volume intensity, duration of exposure and audiometric evaluation. Nevertheless, outcome will also depend on individual variation in tolerance of noise.

Overall, I understand the increasing popularity of the infant sleep machines, as parents would prefer to use them as a non-drug method to soothe their babies to sleep. Sleep disturbances are very frequent in infants and I believe that it is perfectly normal that caregivers are looking for the best way to help their children. Touchette et al. showed that sleep duration within the first 3 years of life is associated with hyperactivity/impulsivity and lower cognitive performance on neurodevelopmental tests at 6 years old. This finding highlights the importance of sleep in brain development and academic performance. The more knowledge science reveals about the importance of sleep, the more parents become stressful to avoid and solve the sleeping problems of their babies.

My other concern is how readily infant sleep machines have reached the market without undergoing a regular approval or oversight by health authorities. However, this research has been very important in raising public awareness of the potential harm of exposing infants to ISM’s loud sound level output and providing policy recommendations for a safer use.

Hugh, S., Wolter N., Propst, E., Gordon, K., Cushing, S., Papsin B. Infant Sleep Machines and Hazardous Sound Pressure Levels, Pediatrics, 2014, Volume 133, Number 4

Touchette et al, Associations Between Sleep Duration Patterns and Behavioral/Cognitive Functioning at School Entry, Sleep, Sep 1, 2007; 30(9): 1213–1219.


Bradley Christensen said...

Hi Carina,

It appears that hearing loss has become a hot topic in our society, with more research being done, and more awareness of the various factors that contribute to hearing loss. With every new device that emits sound, it seems like it is being tested for any repercussions. We already know how dangerous the ipod can be, or a rock concert, but there are some things we haven’t yet taken into account. This is why I liked reading your post. I think most of us can say that as a child, we went to bed with some sound device next to our ears… But who of us were aware that distance from the head and volume had such an effect? When you mentioned that hospital nurseries and neonatal intensive care units are limited to 50dBA measured over 1 hour, I thought that we should be more aware of information like this. I know that companies are simply creating products to make money, and that it is hard for them to be monitored by health authorities, unless the government passes a law to control it.

I’m not sure if you are aware, but a few years ago in England, they passed a law that restricts employees from being exposed to loud noises for too long a duration. Work places now need to monitor their decibel levels, providing the necessary breaks to employees if exposed to noise for too long. They have also been looking at how to help musicians in the Universities who sit in practice rooms with sounds bouncing off the walls. This is a fantastic initiative that other countries should adopt! Now, as I sit here, I start to think about condominium buildings and their air-conditioning units. Are these causing hearing damage as well? It seems that we will only be aware of problems when they have officially been tested.

Thank you for making us aware of this topic and the issues, which need to be addressed!

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