Very low levels of carbon monoxide, such as those found in a roomful of cigarette smokers, can trigger potentially hazardous oxygen shortages in people with heart disease, according to Dr. Thomas E. Dahms of the St. Louis University School of Medicine. The problems were seen at levels of carbon monoxide that are considered safe by federal air quality standards, Dahms reported last week in the New England Journal of Medicine.
In studies with 63 men with coronary artery disease, Dahms found that they could perform 5% less work on a treadmill when their carboxyhemoglobin levels--the combination of carbon monoxide and hemoglobin--reached 2% and 12% less when the level reached 4%. Hemoglobin ordinarily combines with oxygen and carries it throughout the body. Carbon monoxide, however, binds with hemoglobin even more tightly than oxygen does. When people breathe carbon monoxide, it cuts down the amount of oxygen in their blood, and high doses are fatal.
Standards set by the U.S. Environmental Protection Agency allow enough carbon monoxide in the air to take up 2% of the blood's hemoglobin. Dahms said a nonsmoker in a closed room with 20 smokers would breathe enough carbon monoxide to have about a 2% carboxyhemoglobin level. Someone who smokes a pack of cigarettes a day has levels between 4% and 8%.