Sleep Machines May Damage Infant Hearing

As Blake Papsin, MD, otolaryngologist-in-chief at The Hospital for Sick Children in Toronto, was covering for a colleague on the ward one day, he walked into a room and saw a device he had never seen before—an infant sleep machine (ISM).

“The parents told me that a website talked about ISMs and how good they were,” he said. “I asked them to turn it down so we could talk.”

The encounter with the sleep machine in the infant’s room caused Dr. Papsin to head to his laboratory and return with a sound pressure meter. Using the meter, he measured a sound level of 85 A-weighted dB (dBA), which is higher than exposures allowed in industrial work environments without hearing protection.

Some parents use the machines to cover ambient noise and help babies sleep; however, a new study by Dr. Papsin and colleagues, published in the April issue of Pediatrics, is raising some concerns about the machines’ long-term effects on infant hearing (Pediatrics. 2014;133:677-681).

The Study

To conduct the study, the researchers used 14 ISMs widely available in the United States and Canada. Each machine produced between one and 10 different sounds such as white noise, nature sounds, mechanical sounds, and heartbeats. Sound levels were obtained using a sound meter in a sound booth. The meter’s microphone was fitted with a 2-mL coupler to simulate the location of the tympanic membrane in an infant.

The ISM and meter were placed on separate tables of equal heights. Readings were taken at 30 cm to mimic placement on a crib rail or within the crib, 100 cm to simulate placement on a nearby table, and 300 cm to see what levels might be found if the machine was placed across the room. At each distance, the machine was activated three times for 30 seconds each.

“Many parenting websites encourage parents to use these machines at full volume,” said Dr. Papsin. “Some suggest that, at a minimum, the machine has to be louder than the baby’s cry. This led us to do our measurements with the ISMs as loud as they would go.”

Maximum volume sound levels at 30 cm were greater than 50 dBA for all 14 devices, and three machines had output higher than 85 dBA. At middle distances, all ISMs produced sounds higher than 50 dBA. Even at 200 cm, all but one of the ISMs still produced sounds at levels higher than 50 dBA.

“When closer to the crib, three machines produced sounds that exceeded both Canadian and American standards for long-term exposure to noise in industrial environments,” said Dr. Papsin. “Even at maximal distance, most were still above the 50 dBA suggested as the maximal limit in hospital newborn nurseries and neonatal intensive care units.”

The majority of the ISMs tested had volume controls. The researchers recommended that parents consider turning down the volume, placing the machine as far from the baby as possible, and using them for short periods of time only. The authors did not suggest that parents stop using them.

“Although we weren’t able to test children directly, there are a couple of interesting hypothetical predictions from our results,” said Dr. Papsin. “We know that exposure to industrial strength noise over time causes deafness. So, if we exceed these dose-response curves in an infant, it is possible that we may be inducing some hearing loss.”

Other Concerns

Dr. Papsin also noted that developing auditory systems in infants want information content from the environment. Research indicates that the type of auditory input shapes pathways over time. Thus, Dr. Papsin suggests that parents limit the use of white noise, opting instead for more varied sounds such as music or traffic.

However, he thinks otolaryngologists should use consumer interest to start a conversation between parents and physicians; specifically, he hopes they will discuss the concept of sound exposure as a dose of energy.

“When I was a kid, nobody put on suntan lotion, because we did not understand ionizing radiation,” he noted. “When medicine becomes aware of something, the world isn’t ending; it just means we should inform the public of potential risks. Now that we have the attention of parents, the dose of sound is a significant concern because the delicate cochlea we are trained to preserve and protect is threatened by sound throughout the environment.”

Comments from Others in the Field

This is a very important article from both societal and policy standpoints, according to David J. Eisenman, MD, associate professor of otorhinolaryngology-head and neck surgery and director of the Otology and Neurotology Program at the University of Maryland School of Medicine in Baltimore. He said that for more than a decade, there have been concerns regarding links between high noise levels from digital music players and hearing loss in teens. With the concerns raised about ISMs, he sees a risk for what he calls a “double whammy” from two common scenarios.

“There is little doubt that these levels could cause hearing loss, and, because of this, people so affected will need to play things even louder, potentially incurring additional hearing loss, when they are teens,” he said. “This demonstrates the need for guidelines on the sound levels produced by ISMs. Consumers assume that, since it is available for my child, it must be safe.”

Stacey Ishman, MD, MPH, associate professor of otolaryngology and pulmonary medicine at Cincinnati Children’s Hospital, noted possible concerns in both the sleep medicine and surgical sides of her practice. “Potentially, this gives us something else to think about when evaluating patients for hearing loss,” she said. “In addition, we probably should add these concerns when we talk about noise exposures to family.”

John H. Greinwald, MD, a pediatric otolaryngologist at Cincinnati Children’s Hospital, is less sure about the results. While the idea that parents should be conscious about noise exposure in infants is well founded, he is not as convinced that the sound levels are consistently that high in actual use. “Just reading the article, you might think that all of these give off sounds that are way too high for a baby, but I don’t know if parents are really using it that loud and for that long,” he said. “My overall take is that this is more of an awareness study than one saying we should do something.”

Research has not linked ISMs to human disease, as evidenced by the fact that there is no epidemic of hearing loss in infants or very young children. Dr. Greinwald also said that no gold standard for noise levels exists, other than keeping the levels below 90 dBA.

Kurt Ullman is a freelance medical writer based in Indiana.