No other air pollutants studied show a significant and consistent association
MILWAUKEE -- In a seven-city study by Medical College of Wisconsin researchers in Milwaukee, daily levels of carbon monoxide in outdoor air showed a clear and consistent association with corresponding daily rates of hospital admissions for congestive heart failure among the elderly.
The study by Robert Morris, M.D., Ph.D., assistant professor of family and community medicine and director of the Center for Environmental Epidemiology at the Medical College, is published in the October issue of the Journal of Public Health. The association was independent of seasons, temperatures and other major gaseous pollutants.
Patients with congestive heart failure generally have underlying heart disease which limits the heart's ability to deliver an adequate supply of oxygenated blood to the body. Hospital admissions for heart failure represents an aggravation of this underlying condition. According to Dr. Morris, these patients appear to be extremely susceptible to the effects of air pollution.
The researchers studied Medicare hospital admissions data from 1986 to 1989 in seven large cities selected to provide a variety of climates and pollution patterns. Air quality data for Chicago, Detroit, Houston, Los Angeles, Milwaukee, New York and Philadelphia, were taken from the Aerometric Information and Retrieval System maintained by the Environmental Protection Agency (EPA).
On average, more than 3,000 annual hospital admissions in the seven cities for heart failure, representing 5.7 percent of total admissions, could be attributed to airborne levels of carbon monoxide. The estimated annual hospitalization cost alone is $33 million. None of the other pollutants studied (ozone, sulphur dioxide and nitrogen dioxide) showed consistent, significant association with heart failure.
The strength of association between carbon monoxide pollution and hospital admission rates for heart failure was highest in Los Angeles followed by Detroit, Milwaukee, Houston, Chicago, Philadelphia and New York. According to Dr. Morris, the variability in this association may, in part, reflect how well the monitoring system describes the exposure of people in these cities. "This is because data from outdoor air monitoring used in the study provides a rough approximation of individual exposure which tends to occur indoors far from the monitoring equipment. To the extent that the true exposure is obscured, the magnitude of the observed association decreases."
In a related editorial, Dr. Joel Schwartz of the Department of Environmental Health at the Harvard School of Public Health, notes that this and other studies indicate it is time to reevaluate not only the carbon monoxide standard but the EPA's basis for setting it.
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