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While an incubator can save the life of a premature baby, it may be contributing to hearing loss in these vulnerable infants.
A new study published March 27 in Frontiers in Pediatrics assessed the sounds in the neonatal intensive care unit, evaluating the impact on newborns.
“The motivation of our multidisciplinary research team concerns the question: why many more premature babies suffer hearing impairments,” said study author Christoph Reuter, of the University of Vienna in Austria.
“We believe that what we have measured in our studies could be a leading cause," he said in a journal news release. "However, to understand how to protect premature infants from such noise levels, precise environment information is needed.”
In the womb, the fetus hears low-frequency sound muffled by amniotic fluid, and no abrupt noises.
Sounds in incubators are much less muffled. There are many high-frequency components and abrupt noises. Recommended noise limits have been established, but these are often exceeded, especially when incubators are handled or opened, researchers said.
“Our study focused on various real-life noises and their levels as well as on their timbral characteristics, with two main purposes,” said co-author Matthias Bertsch from the University of Music and Performing Arts Vienna. “Firstly, describing the NICU and incubator environment; secondly, providing awareness by presenting interactive material of real-life situations.”
The study used a mannequin placed in an incubator equipped with measurement microphones.
Researchers recorded different sounds both inside and outside the incubator. Then they analyzed decibel levels to determine how sounds had been modified by the incubator.
While the incubator dampened most sounds, it caused certain ones to resonate within its cavity. This created a booming effect and raised the noise level by up to 28 decibels.
While sound inside the incubator was much louder than sound outside it, individuals outside the incubator didn't perceive it as loud.
“As closed boxes, incubators usually have an inherent resonance at around 100 Hz," meaning sounds inside are "exceptionally loud," said senior author Vito Giordano of the Medical University of Vienna. “Noises from the outside sound more tonal inside the incubator, booming and muffled as well as less rough or noisy, because of this resonance.”
Both weighted decibel levels (which are adjusted to account for the range of human hearing) and unweighted decibel levels were assessed.
The authors said the unweighted levels measured were much higher than the weighted ones, which significantly underestimated the noise preemies were exposed to.
Weighting is only an accurate reflection of sounds at lower levels, and is designed for adult ears, which are sensitive at different frequencies, they noted.
“Our results are not generalizable to all incubators available on the market,” Reuter said. “Moreover, we measured in a simulation room under ideal conditions and not under everyday conditions, where the sound generated by the environment would be even louder.”
The aim is not to deprive babies of all sound, the authors said. For their own development, it's good for infants to be able to hear things happening around them.
They said, however, that there is a need to take sound into account when designing and using incubators.
Hearing impairment can lead to delays in infants' language development.
The March of Dimes has more on hearing loss in infants.
SOURCE: Frontiers in Pediatrics, news release, March 27, 2023
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