No other air pollutants studied show a significant and consistent association
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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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