CO's
attack on the brain
As CO is inhaled, it enters the bloodstream and attaches to
hemoglobin, the protein
in red blood cells that carries oxygen. CO, however, displaces
oxygen because it binds to hemoglobin 200 times tighter than
oxygen does. The body can't get enough oxygen-a condition called
anoxia.
Besides causing anoxia, CO is also toxic to cells. It triggers
a biochemical cascade that, if uninterrupted, can continue
to damage the cells even after the exposure to the gas has
stopped, according to Hopkins. That may be why current research
shows that individuals with anoxic brain injury tend to have
less recovery than those with physical injuries to the brain.
Starving the brain
In the brain, which consumes about 20 percent of the body's
total oxygen, there appears to be a hierarchy of ways in which
anoxia exerts its damaging effects. Three brain structures,
the hippocampus,
the cerebellum,
and the basal ganglia,
"seem to be more vulnerable than other parts of the brain,"
Hopkins explains. The hippocampus, the region of the brain
responsible for transferring new information to long-term
memory,
is most vulnerable because it sits deep in the middle of the
temporal lobe, at the very end of the blood's circulation
route. In addition, during low oxygen conditions the neurons
in the hippocampus release a chemical called glutamate
at higher-than-normal levels. This is toxic to brain cells.
Firsthand experience
Hopkins has firsthand experience with the effects of anoxia
on the brain. In 1981, her eldest son, four years old at the
time, was pinned across his chest by a garage door. He was
comatose for several weeks and suffered serious anoxic brain
injury. "We spent years doing therapy, and I kept asking,
'Where's the research? What can we expect?' And I really wasn't
getting any answers." Hopkins, a nurse by profession,
decided to find the answers herself and went to graduate school
to investigate the effects of anoxia on the brain.
In 1996, Hopkins received her Ph.D. She has found her research
on anoxia very satisfying personally and professionally. "I
love what I do," she says. "Just getting information
out regarding the effects of anoxia and the long-term outcome
has really helped a lot of people. When I tell patients about
my son, they realize that I understand what they're going
through and they're willing to be involved in my research."
(Her son, now 25, graduated from high school and works for
a local business.)
Consequences of CO poisoning
In her studies, Hopkins has documented a variety of damaging
effects on the brain after CO exposure. Initially, brain scans
may reveal small spots of damaged brain cells. "Those
tend to occur within the first 24 to 48 hours after exposure,"
she notes. Over time, signs of cell loss, or atrophy, appear.
"It takes a while for the cells to die and be broken
down by other cells and removed. That process doesn't happen
immediately. We see atrophy at two weeks up to 12 months after
CO exposure."
On average, 25 to 50 percent of the CO-poisoning victims in
her studies have cognitive impairments. Some experience a
memory impairment known as anterograde
amnesia: the inability to form new memories. While memories
from before the brain injury remain intact, the person has
trouble learning and remembering new information, such as
lists of information and the names of new acquaintances. In
some cases, the impairments interfere with the person's ability
to hold a job or live independently.
The degree of memory impairment appears to be directly related
to the amount of damage sustained by the hippocampus. In fact,
the extent of damage visible on magnetic
resonance imaging (MRI) roughly predicts the amount of
impairment. Although some impairments may improve as the person
recovers from the incident that caused the anoxia, memory
function may continue to decline. Thus, even if a person survives
CO poisoning, the resulting memory impairments can last a
lifetime.
Hidden victims
Each year, approximately 50,000 people are seen at hospitals
for CO poisoning, says Hopkins. She suspects many more cases
are not diagnosed because the symptoms often resemble those
of the flu, including nausea, headache, lethargy, and dizziness.
Poisoning can occur even with small amounts of CO, if inhaled
over a long time. "Any kind of incomplete combustion
gives off carbon monoxide," explains Hopkins. For example,
"if people have an attached garage and warm their cars
up in the garage, they may be getting carbon monoxide pulled
into the house." Just the exhaust from a gas stove that's
not burning efficiently can cause CO poisoning. "We've
seen a few cases around Thanksgiving when people cook a lot."
Other sources of carbon monoxide include faulty furnaces,
gas appliances, gas fireplaces, kerosene or propane space
heaters, and charcoal grills.
Act quickly
If you suspect you're suffering from CO poisoning, immediately
get to a well-ventilated area and seek medical attention.
A blood test can determine whether you've been exposed. The
treatment for CO exposure is oxygen, which, stresses Hopkins,
"is important to get as soon as possible." Since
CO itself has no odor or color, Hopkins advises, "the
best thing to do is to buy a carbon monoxide detector. They
cost $30 to $50, which is much less than it costs to go to
the emergency room, even if you have a good outcome."
Further Reading:
"MRI, quantitative MRI, SPECT, and neuropsychological
findings following carbon monoxide poisoning brain injury,"
by Shawn D. Gale, Ramona O. Hopkins, Lindell K. Weaver, Erin
D. Bigler, Edgar J. Booth, and Duane D. Blattner. (Brain Injury,
1999, Volume 13, Number 4, 229-243.)
"Continuing decline of memory skills with significant
recovery of intellectual function following severe carbon
monoxide exposure: clinical, psychometric, and neuroimaging
findings," by Cecil R. Reynolds, Ramona O. Hopkins, and
Erin D. Bigler. (Archives of Clinical Neuropsychology, 1999,
Volume 14, Number 2, pp. 235-249.)
Contact Information:
National Institute of Neurological Diseases and Stroke
Anoxia/Hypoxia Information Page
http://www.ninds.nih.gov/health_and_medical/disorders/anoxia_doc.htm
Brain Injury Association
105 North Alfred Street
Alexandria, VA 22314
Email: publicrelations@biausa.org
Website: http://www.biausa.org
Tel: 703-236-6000 800-444-6443
Fax: 703-236-6001
National Rehabilitation Information Center (NARIC)
1010 Wayne Avenue
Suite 800
Silver Spring, MD 20910-5633
Email: naricinfo@kra.com
Website: http://www.naric.com
Tel: 301-562-2400 800-346-2742
Fax: 301-562-2401
Head Injury Hotline
600 First Avenue
Suite 212
Seattle, WA 98104-2221
Email: brain@headinjury.com
Website: http://www.headinjury.com
Tel: 206-621-8558
Fax: 206-624-4961
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