Doctors Study Infant Incubator Noise Levels
Noise levels which can permanently
destroy hearing are sonnething we've
come to expect in boiler factories, cotton
gins, textile mills, airports and even
discotheques.
But not in infant incubators.
Now researchers at Duke and the
National Institute of Environmental
Health Sciences have suggested that
incubator noise levels may be a possible
cause of hearing loss in infants.
Dr. Joseph C. Farmer, an assistant
professor in otolaryngology at Duke, and
Dr. Stephen A. Falk of the NIEHS have
measured the noise levels in standard
incubators and found them to be well
below industrial noise limits allowed by
federal law.
But those standards are based on
exposure levels for adults for an
eight-hour work day. Farmer said. No one
yet knows the effects of loud, continuous
noise on a newborn infant, particularly
.when that noise may continue
uninterrupted for weeks or even months.
"We need to establish some kind of
damage-risk criteria for noise exposure
levels for infants and then design the next
generation of incubators to meet these
criteria,” Farmer said.
Farmer and Falk measured noise levels
in six incubators. Each was analyzed
twice, with the microphone of the sound
level meter placed where the infant's head
would normally rest, and then placed
where the feet would be. They found no
difference between the levels in the two'
positions.
The measurements revealed an average
linear noise level of 74.5 decibels and an
A-weighted level of 57.7 decibels. The
linear measure is the average noise of all
frequencies. The A-weighted
measurement suppresses some of the low
sound frequencies in much the same way
as the human middle ear does and thus
gives a closer approximation of the actual
noise levels transmitted to the inner ear.
The source of the noise was found to
be the electric motor and fan below the
infant compartment of the incubator.
Federal regulations for industrial noise
will allow a maximum of 90 decibels,
A-weighted for a duration of eight hours
a day. With a sound level of 115 decibels,
the law allows only a 15-minute or less
exposure per day.
According to industrial criteria.
Farmer said, the noise levels found in
incubators would not be considered a risk
to hearing. But he said there are several
reasons why this should be reevaluated.
First, the present criteria were based
on adult studies and are possibly not
applicable to noise exposure in infants.
Second, he said, continuous noise is
potentially more damaging than
intermittent noise, which provides an
opportunity for some recovery. A
premature infant in an incubator is
subjected to continuous noise levels for
weeks or months.
Third, he said, some studies have
shown that exposure to loud noise
increases the potential damage to the
inner ear from certain types of
antibiotics. He said the use of these
potentially ototoxic antibiotics on
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VOLUME 20, NUMBER 34
AUGUST 24,1973
DURHAM, NORTH CAROLINA
Dive Tests Breathing Mix
In Hyperbaric Chamber
newborns in incubators should be studied
and limited to use in those infection cases
in which these antibiotics are the only
effective drugs, as shown by appropriate
microbiological studies.
Farmer said the American public has a
higher frequency of neurosensory hearing
loss than people in other areas of the
world and doctors believe a significant
amount of this is due to noise.
"Noise is like other environmental
problems," Farmer said. "The public
really hasn't become concerned until the
last few years."
"But noise as a cause of sensorineural
hearing loss has been well established for
some time," he said.
Loss of hearing due to noise is a
cumulative condition. Once hair cells in
the inner ear have been irreversibly
damaged by loud noise, they are not
replaced. As persons grow older,
arterioschlerosis and impaired inner ear
blood flow can also cause hair cells to die,
leading to a condition called presbycusis.
Farmer said in older persons it is
sometimes hard to tell the cause of
sensorineural hearing loss, aging or noise
or both. But when significant
sensorineural hearing losses are seen in
younger people, it is frequently due to
excessive noise exposure, which can occur
in multijsle situations such as factories,
firearms and loud music.
Hearing aids are often not much help
for presbycusis or noise-induced hearing
loss, he said, because although the aids
amplify sound, the person has lost the
ability to discriminate pitch and
frequency and differentiate between
sounds, and hearing aids cannot perform
(Continued on page 3)
A month-long series of simulated dives
began today in the medical center
hyperbaric chamber to test a new
three-gas breathing mixture which could
permit man to dive farther beneath the
sea, and with greater safety, than is now
possible.
Two of the six dives in the series will
be to a simulated depth of 1,000 feet
below sea level. In one of the deep dives,
the four divers will breathe the
helium-oxygen mixture now standard for
deep sea work. In the other the divers will
breathe a mixture of helium, oxygen and
nitrogen. This will be the first time that
nitrogen has been used at this depth.
Nitrogen has not been used in deep
diving because of its narcotic or
intoxicating effect at depths greater than
100 feet. But the helium in the deep
diving mixtures now used also causes
problems—a phenomena called High
Pressure Nervous Syndrome which comes
on at depths of 500 feet or greater.
HPNS is characterized by nausea,
dizziness and tremors, and the symptoms
become more severe with increasing
depth. This phenomenon has limited the
depth to which man can safely dive.
Dr. Peter B. Bennett, professor of
anesthesiology and an internationally
tnown authority on the physiological
problems of diving, will direct the
experimental dives.
Bennett said animal experiments and a
few human studies have shown that the
effects of HPNS cian be negated by adding
a certain amount of anesthetic or narcotic
gas such as nitrogen to the helium-oxygen
diving mixture. It also has been shown, he
said, that the effects of the nitrogen
narcosis which then result can be relieved
with increasing pressure.
Thus, if just the right balance can be
found between helium and nitrogen,
Bennett said, it may be possible for divers
to overcome the effects of both narcosis
and HPNS and work at much greater
depths than ever before. Other
detrimental effects of helium, such as
voice distortion—the "Donald Duck"
effect—and the extreme loss of body
heat, might also be overcome.
Three of the divers have been provided
by the Harbor Branch Foundation and
the other one from Oceaneering
International Inc. of Houston, Tex. The
F.G. Hall Laboratory for Environmental
Research and the Department of
Anesthesiology are conducting the
research.
The dive which began today is to a
depth of 192 feet. The divers are using
compressed air, which contains 79 per
cent nitrogen and 21 per cent oxygen.
On Aug. 28 the divers will be taken to
720 feet using the three-gas mixture, then
on Sept. 5 or 10 they will go to 720 feet
breathing helium and oxygen.
On Sept. 21 there will be another
compressed air dive to 272 feet. The first
1,000-foot dive will come Sept. 25 using
the three-gas mixture, then on Oct. 2
another dive to 1,000 feet using helium
and oxygen will complete the series.
Very rapid compression times will be
used, with the divers going from the
'•surface" to a pressure equivalent to
1,000 feet below the sea in only 20
minutes. They will remain there for about
an hour. Decompression from this depth
will take about three days. The divers will
come out of the hyperbaric chamber
between each dive for rest and testing.
The divers will be in a dry chamber
throughout the dives except during the
decompression period of the two
helium-oxygen dives. Then a tank below
the pressure chamber—the "wet
pot"—will be filled with water and the
divers will test some equipment for
(Continued on page 2)
m
AN EAR FOR NOISE—Dr. Joseph C. Farmer (standing), assistant professor of
otolaryngology, checks an incubator motor with Dr. Stephen A. Falk of the National
Institute of Environmental Health Sciences. The two measured noise levels inside
several types of incubators and suggested that this noise could be a possible cause of
infant hearing loss. The noise comes from the motor and fan under the infant
compartment. (Photo by Jimmy Wallace)