| Carbon Monoxide and Hospital Admissions for Congestive Heart Failure: Evidence of an Increased Effect at Low Temperatures Robert D. Morris and Elena N. Naumova Department of Family Medicine and Community Health, Tufts University School of Medicine, Boston, MA 02111 USA Abstract
The combined effects of carbon monoxide and low temperature on daily variation in hospital admissions for congestive heart failure (CHF) were examined for a 4-year period in Chicago, Illinois. Medicare hospital admissions for CHF were analyzed as a function of the maximum hourly temperature, maximum hourly levels of carbon monoxide (CO) , and other criteria pollutants in Chicago for each day of the 4-year period (1986-1989) . The regression analyses for the time series were conducted using single and multipollutant models with interaction terms and adjustments for weather, weekly cycles, seasonal effects, and secular trend. The data were also grouped into three temperature ranges, <40°, 40°-75°, and >75° F, and the relationship between CO and CHF admissions was evaluated for each range. For the 4-year time series, the CO level was positively associated with hospital admissions for CHF in the single pollutant and multipollutant models after adjustment for seasonal effects and weather pattern. The relative risks of hospital admissions for CHF in Chicago associated with the 75th percentile of exposure to CO in the high, medium, and low temperature ranges were 1.02 [95% confidence interval (CI) , 0.95-1.10], 1.09 (CI, 1.04-1.14) , and 1.15 (CI, 1.09-1.22) , respectively. In these data, the effect of CO on hospital admissions for CHF was temperature dependent, with the magnitude of the effect increasing with decreasing temperature. This synergy may help to explain the association between ambient CO and CHF admissions demonstrated in other studies. Key words: air pollution, carbon monoxide, elderly, heart failure, Medicare, synergy, temperature, time series. Environ Health Perspect 106:649-653 (1998) . [Online 14 September 1998] http://ehpnet1.niehs.nih.gov/docs/1998/106p649-653morris/ abstract.html Address correspondence to R.D. Morris, Department of Family Medicine and Community Health, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111 USA. This work was supported by a research grant R29-ES07204-01A2 from the National Institutes of Health. We thank Jerome Sacks and Patricia Styer for their assistance in obtaining particulate data. We also acknowledge the comments of Douglas Dockery and the reviewers of our initial manuscript. Received 18 February 1998 ; accepted 23 June 1998.
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