Carbon Monoxide

From: Health Problems Caused By Other Combustion Products
(Stoves, Space Heaters, Furnaces, Fireplaces)
Co-sponsored by: The American Lung Association (ALA),
The Environmental Protection Agency (EPA),
The Consumer Product Safety Commission (CPSC), and
The American Medical Association (AMA)
U.S. Gov't Printing Office Publication No. 1994-523-217/81322 1994

Carbon monoxide is an asphyxiant. An accumulation of this odorless, colorless gas may result in a varied constellation of symptoms deriving from the compound's affinity for and combination with hemoglobin, forming carboxyhemoglobin (COHb) and disrupting oxygen transport. The elderly, the fetus, and persons with cardiovascular and pulmonary diseases are particularly sensitive to elevated CO levels. Methylene chloride, found in some common household products, such as paint strippers, can be metabolized to form carbon monoxide which combines with hemoglobin to form COHb. The following chart shows the relationship between CO concentrations and COHb levels in blood.

Tissues with the highest oxygen needs -- myocardium, brain, and exercising muscle -- are the first affected. Symptoms may mimic influenza and include fatigue, headache, dizziness, nausea and vomiting, cognitive impairment, and tachycardia. Retinal hemorrhage on funduscopic examination is an important diagnostic sign, but COHb must be present before this finding can be made, and the diagnosis is not exclusive. Studies involving controlled exposure have also shown that CO exposure shortens time to the onset of angina in exercising individuals with ischemic heart disease and decreases exercise tolerance in those with chronic obstructive pulmonary disease (COPD).

Note: Since CO poisoning can mimic influenza, the health care provider should be suspicious when an entire family exhibits such symptoms at the start of the heating season and symptoms persist with medical treatment and time.

Relationship between carbon monoxide (CO) concentrations
and carboxyhemoglobin (COHb) levels in blood

Predicted COHb levels resulting from 1- and 8-hour exposures to carbon monoxide at rest (10 l/min) and with light exercise (20 l/min) are based on the Coburn-Foster-Kane equation using the following assumed parameters for nonsmoking adults: altitude = 0 ft; initial COHb level = 0.5%; Haldane constant = 218; blood volume = 5.5 l; hemoglobin level = 15 g/100ml; lung diffusivity = 30 ml/torr/min; endogenous rate = 0.007 ml/min.

Source: Raub, J.A. and Grant, L.D. 1989. "Critical health issues associated with review of the scientific criteria for carbon monoxide." Presented at the 82nd Annual Meeting of the Air Waste Management Association. June 25-30. Anaheim, CA. Paper No. 89.54.1, Used with permission.

Carboxyhemoglobin levels and related health effects

% COHb in blood	Effects Assocated with this COHb Level
80	Death^a
60	Loss of consciousness; death if exposure continues^a
40	Confusion; collapse on exercise^a
30	Headache; fatigue; impaired judgement^a
7-20	Statistically significant decreased maximal oxygen consumption during strenuous exercise in healthy young men^b
5-17	Statistically significant diminution of visual perception, manual dexterity, ability to learn, or performance in complex sensorimotor tasks (such as driving)^b
5-5.5	Statistically significant decreased maximal oxygen consumption and exercise time during strenuous exercise in young healthy men^b
Below 5	No statistically significant vigilance decrements after exposure to CO^b
2.9-4.5	Statistically significant decreased exercise capacity (i.e., shortened duration of exercise before onset of pain) in patients with angina pectoris and increased duration of angina attacks^b
2.3-4.3	Statistically significant decreased (about 3-7%) work time to exhaustion in exercising healthy men^b

SOURCE: aU.S. EPA (1979); bU.S. EPA (1985)

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