Background There is a yearly increase in the rate of sudden unexplained death （SUD）, even through extensive physical examination and the testing of a large number of biomarkers, the cause of sudden death in patients previously in good health cannot be fully determined. During clinical practice, a spatial aggregation phenomenon has been observed in the incidence of sudden unexplained death. Previous research has shown that environmental factors, such as air pollution, weather conditions, etc., have a significant impact on human health. In the wake of the continuous environmental damage, the relationship between environmental factors and sudden unexplained death still needs to be studied. To study the relationship between sudden unexplained death and air quality and temperature, commonly used markers such as particulate matter of aerodynamic diameter 〈10 μm （PM10）, daily average concentration of the gaseous pollutants sulfur dioxide （SO2） and nitrogen dioxide （NO2）, and the daily average temperature were investigated. Methods The methods include collecting the data of sudden unexplained death; air quality monitoring; meteorological monitoring from January 1, 2005 to December 31, 2008; utilizing generalized additive models （GAM）; controlling the influential factors such as secular trend, seasonal trend, and Sunday dummy variable; and analyzing the correlation between daily inhalable particle concentration, daily average temperature, and the number of daily SUD. Results There was no statistical significance between the daily inhalable particle and daily incidence of sudden unexplained death. Incidence rate of sudden unexplained death had nonlinear positive correlation with daily temperature. When the temperature was 5℃ above the daily average temperature, the daily incidence of sudden unexplained death went up with the rising temperature. Conclusion Temperature may be one of the key risk factor or precipitating factor of SUD.
Background Underlying diseases have a statistically significant positive correlation to sudden death. However, sudden unexplained death （SUD） is different from sudden death, as there is no clinical evidence to support the sudden death due to the original underlying disease, nor a lethal pathological basis to be found during autopsy. In addition, SUD are more common in young, previously healthy individuals, usually without any signs of disease, with no positive lesions found after autopsy. Therefore, a causal relationship between SUD and the underlying disease needs to be further explored. This study aimed to explore the role that common underlying diseases play in patients with SUD and to reveal the correlation between them. Methods The medical records, history and case information of 208 patients with SUD were collected for the survey. All these SUD occurred in the emergency room of Peking University Third Hospital from January 2006 to December 2009. The patients were stratified by with and without common underlying diseases. To examine possible associations between the underlying diseases and the cause of unexplained sudden death, the chi-squared and Fisher＇s exact tests were used. Results Among the 208 patients, 65 were diagnosed with common underlying diseases while 143 were not. Within these two groups, there were 45 patients for whom the clear cause of death was determined. However, there were no statistically significant differences or strong associations （x2=1.238, P 〉0.05） between the 11 patients with （16.90%） and 34 without （23.78%） common underlying disease among these 45 patients. We also found that occurrence of the common underlying diseases, such as neurological system, cardiovascular and pulmonary system diseases, are not statistically significant （P 〉0.05） in the diagnosis of the SUD. Conclusion Common underlying diseases make no obvious contributions to SUD and are not useful in diagnosing the underlying reasons for death.
TIAN Zhao-xingLV Yan-yuChetan Rai NugessurYAN WeiZHAO Wen-kuiKONG Li-liZHENG Ya-an
