Life-saving intensive-care incubators play a critical role in a newborn’s start to life, but researchers have found that they may also be exposing babies to louder, resonating sounds that increase the risk of damaging their sensitive hearing.
While noise in the neonatal intensive care unit (NICU) and its impact on its vulnerable patients has been the subject of many studies, these new findings shed new light on the incubators in which the babies spend their first days, weeks or sometimes even months in.
In the collaborative study out of the Medical University of Vienna (MUV), with scientists from Hamburg, Munich and Osnabruck, detailed sound measurements taken from a complex simulation of models within and outside incubators found that certain frequencies resonated inside the space, increasing the noise level by up to 28 decibels.
“The motivation of our multidisciplinary research team concerns the question: why many more premature babies suffer hearing impairments,” said co-author Christoph Reuter from the University of Vienna. “We believe that what we have measured in our studies could be a leading cause. However, to understand how to protect premature infants from such noise levels, precise environment information is needed.”
The NICU itself is a noisy environment, often tipping over the 45-dB level recommended by the American Academy of Pediatrics. Hearing impairment occurs in 2-10% of preterm babies who require incubators, as opposed to 0.1% in non-NICU newborns.
While noise has a variety of negative immediate impacts such as apnea, hearing impairment at this age can lead to more long-term issues such as delays in language development. Incubators dampen a lot of the NICU’s sound levels, but this study suggest it’s not as complete as first thought.
“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.”
In the study, a manikin and measuring microphones were placed inside an incubator and exposed to a range of NICU sounds at the Pediatric Simulation Center at the MUV. They were then analyzed to see how the incubator had moderated the sounds, measuring weighted (dBA) and unweighted decibels (dB). The former is the measurement scaled for human hearing ranges.
Unlike in the womb, where most sounds are muffled by the amniotic fluid and are delivered in low frequencies, incubator environments have high-frequency elements and abrupt sounds, especially when handled or opened. Because the outside environment is comparatively louder, the noise of this interaction with the incubators was underestimated.
“As closed boxes, incubators usually have an inherent resonance at around 100 Hz,” said senior author Dr Vito Giordano from the MUV. "In this range sounds inside the incubator are exceptionally loud.”
While studies often focus on weighted decibel levels to determine sound exposure, the researchers say that this measurement caters to adult ears. Their results showed much higher levels of unweighted decibels, suggesting that usual methods of measurement significantly underestimated noise babies in incubators are exposed to.
“Our results are not generalizable to all incubators available on the market,” cautioned Reuter. “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 researchers add that while sound is an important sensory aspect of development for newborns, there should be more awareness of just how sounds resonate inside incubators. This could inform better design and use of this vital medical equipment and mitigate the risk of hearing damage.
The study was published in the journal Frontiers in Pediatrics.
Source: The University of Vienna
