[The association between emergency clinic visits for asthmatic attacks and fluctuating environmental factors]

The number of nocturnal visits of asthmatic attack patients to the emergency room of Yokohama Medical Association's Clinic from January 1990 to December 1991 was compared to daily levels of air pollution (NO, NO2, SO2 and SPM) and weather (temperature and relative humidity) variables measured in Yokohama City. Trend-cycle components (Trend) that control for the weekly effects, other irregular variance for asthmatic attack incidence and environmental parameter measurements were estimated from the original data series using the method of Akaike and Ishiguro (1980). The rate of increase for each environmental parameter was then calculated from its trend-cycle components. We classified the data into four stages on the basis of rising and falling temperature and humidity. For each stage of temperature and humidity, fluctuation we estimated correlations between the number of asthmatic attack visits and original data series measurements, estimated trend-cycle components, and calculated rates of increase for each of the air pollutants. The daily number of asthmatic attack visits was negatively correlated to the daily mean values of all air pollutants, but positively correlated to the daily mean temperature and relative humidity. The trend-cycle components of the air pollutants were also negatively correlated to the frequencies of asthmatic attacks (p < 0.01 for all pollutants except NO2). In contrast, the number of asthmatic attack visits were in general positively correlated with increasing levels of pollutants. Furthermore, when both temperature and relative humidity decreased, significant correlations (r > 0.31, p < 0.001) between the number of asthmatic attacks and increased rates of all air pollutants were observed (r: NO2 > NO > SO2 > SPM).