Carbon Monoxide May Affect Infant Hearing

Chronic Low Level Carbon Monoxide Exposure Impairs Hearing Development in Rats

From the WebMD Archives

Oct. 17, 2003 - Hundreds of Americans die each year and thousands are hospitalized due to carbon monoxide poisoning. In these cases, people are exposed to high levels of the toxic gas, but intriguing early research suggests that even very low levels of exposure may impair hearing development in human infants.

In a series of studies involving newborn rats, researchers found that prolonged, low-level exposure to carbon monoxide affected auditory development. The symptoms they saw in the developing rats were similar to those seen in children with a poorly understood hearing disorder known as auditory neuropathy.

Children with the disorder have normal hearing sensitivity, but they process sounds abnormally and cannot make sense of what they are hearing. They are often labeled as autistic because they fail to develop language skills, auditory researcher Janet E. Stockard-Sullivan, PhD, tells WebMD.

"We have no proof whatsoever that the rats in these studies had this disorder, but it is an interesting parallel that certainly deserves further study," she says. "These findings suggest the possibility that even levels of carbon monoxide exposure that are generally considered safe could pose a risk to babies and young children."

300 Die Each Year in U.S.

Carbon monoxide is lethal to humans at concentrations of around 1,000 parts per million (ppm) and above, but levels up to around 50 ppm are generally considered safe exposure levels for humans by the Health and Safety Executive. In the three studies, to be published in the December issue of the Journal of Neuroscience Research, rat pups were exposed to chronic and low levels of carbon monoxide between 12 and 100 ppm during a period of rapid hearing development.

They found that exposures well under 50 ppm caused measurable hearing loss and other auditory nerve developmental problems. In a separate study, they also confirmed damage to the hearing apparatus of the inner part of the ear that transmits signals to the brain with chronic and mild levels of carbon monoxide beginning at 25 ppm.

"It is too soon to tell whether these findings are significant to humans, but it is clear that we need to look more closely at carbon monoxide exposure," says investigator John Edmond, who led the research team.

Edmond says people die needlessly because they either don't know the risks or ignore them. According to figures from the U.S. Consumer Products Safety Commission, 300 fatalities occur each year from exposure to the invisible, odorless gas. The gas enters the lungs and interrupts the normal supply of oxygen in the blood, which can increase the risk of damage to the heart, brain, and other vital structures. The symptoms of carbon monoxide poisoning include headaches, dizziness, nausea, and convulsion. In people with underlying medial conditions such as heart disease it can cause chest pain. It can also cause flu-like symptoms that clear up after leaving the home. At very high concentrations it can be lethal.

Things to Do, and Not Do

Because carbon monoxide is produced when fuel is burned, any fuel-burning appliance in your home is a potential source of the gas. It is important to have good ventilation in your home, maintain all your home appliances, and have reliable detectors installed in your home. To reduce your risk, the CPSC recommends taking these steps:

  • Make sure appliances are installed according to manufacturer's instructions and building codes.
  • Have the heating system (including chimneys and vents) inspected each year and examine vents and chimneys regularly for improper connections, visible rust, or stains.
  • Follow manufacturer's directions for safe appliance operation, and address problems that could indicate improper operation such as decreasing hot water supply, a poorly working furnace, soot on appliances, or an unfamiliar burning odor.
  • Install a carbon monoxide detector.

What shouldn't you do?

  • Never burn charcoal indoors or in a garage.
  • Never service appliances without the proper knowledge, skills, and tools.
  • Never use the gas range or oven for heating.
  • Never leave a car running in the garage, even for a few minutes.
  • Never operate unvented gas-burning appliances in a closed room.

CPSC spokesman Ken Giles tells WebMD that improper use of portable home generators is a growing problem.

"We have been seeing more and more deaths from generators being used indoors, in basements, and in attached garages," he says. "There can even be problems if the generator is placed on a porch next to an open window."

Giles says generators should only be operated outdoors in a well-ventilated, dry area; away from air intakes to the home.

Show Sources

SOURCES: Journal of Neuroscience Research, December 2003. John Edmond, PhD, Mental Retardation Research Center, David Geffen School of Medicine, UCLA. Janet E. Stockard-Sullivan, PhD, department of pediatrics, University of South Florida, Tampa. Ken Giles, spokesman, U.S. Consumer Product Safety Commission.
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