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Pollution and Cerebrovascular Disease
Source: Tsai SS, et al. Evidence for an association between air pollution and daily stroke admissions in Kaohsiung, Taiwan. Stroke 2003;34:2612-2616.
Goal: To explore the relationship between hospital admissions for stroke and the concentration of specific air pollutants over a four-year period.
Design: Retrospective, case-crossover study.
Subjects: All people admitted for cerebrovascular disorders (CVD) in the region from 1997 to 2000.
Methods: Computerized medical records available through the National Health Insurance Program of Taiwan were reviewed, and those with admission diagnoses of stroke were pulled. For each date of admission, air pollution data were extracted from six air-quality monitoring stations in Kaohsiung and averaged. The pollutants measured were SO2, PM10, NO2, CO, and O3. Air pollution levels on admission dates were compared with levels obtained one week before and one week following hospital admission.
Results: Evaluating single pollutants, admissions for primary intracranial hemorrhage, and ischemic stroke (IS) were significantly associated with all pollutants, except SO2, on warm days. On cool days, only IS admissions and CO levels were associated significantly. Two-pollutant models again showed an increased rate of admission for CVD with specific combinations of elevated pollutants, except in the case of SO2.
Conclusion: There is an association between short-term severity of air pollution and hospital admission for stroke (most notably for PM10 and NO2).
Study strengths: Capture of information; multiple sites available for measuring air pollution.
Study weaknesses: Study was performed in a tropical climate, making generalizability suspect; would have been interesting to note how many people admitted for CVD also smoked; population-based averages of pollutant levels may not equal individual ambient exposure; the limitations of retrospective analysis.
Of note: Kaohsiung has a population of almost 1.5 million people, has mild winter temperatures, and is Taiwan’s biggest commercial harbor; the number of stroke admissions reportedly varied according to day of the week.
We knew that: Previous studies noted an association between levels of air pollution on a given day and hospitalization or death due to respiratory or cardiovascular events; exposure to specific air pollutants may result in increased coagulability, raised plasma viscosity, and increased heart rate.
Clinical import: Most are aware of existing research pointing to a higher incidence of asthma exacerbation when air quality levels drop. Now come data suggestive of significant cerebrovascular consequences as a result of rising levels of air pollutants. Support of tough clean air initiatives that maintain economic viability, and a push for additional funding for research into the use of clean alternative fuels, would appear to be worthy causes all could get behind. In the meantime, recommending that patients at risk for CVD take measures to limit exposure to air pollution and increase dietary intake of fruits and vegetables makes sense.
What to do with this article: Keep a copy on your computer.
Dr. Greenfield, Medical Director, Carolinas Integrative Health, Carolinas HealthCare System, Charlotte, NC, is Executive Editor of Alternative Medicine Alert.