| BackgroundWith the impact of global warming,the frequency and the severity of extreme weather events are increasing across the globe.The highest and lowest of temperature and humidity have fluctuated over time and constantly set records in some regions.Rising temperature leads to drought,forest fires,and extreme weather events such as cold spells and heat waves.Adverse health outcomes of extreme weather had gained more and more attention.Epidemiological studies have shown show that extreme temperature is associated with the occurrence,exacerbation and mortality of cardiovascular diseases,but the association between extreme weather events and acute myocardial infarctions(AMI)hasn't been closely examined.There is currently no unified definition for cold spells and heat waves across the research field.Considering that climatic conditions,geographical factors,and human behaviors vary widely between countries and regions,the results of previous studies on the association between extreme weather events and health in the western countries cannot be directly applied in China.At present,the health outcome studies of cold spells and heat waves in China are mostly focused on mortality.There is by far no research on the impact of cold spells and heat waves on the hospitalizations of cardiovascular diseases.Few studies have addressed the health outcomes of ambient relative humidity.These studies have limitations of small sample sizes,short study period,data collection from single or several hospitals,methodological shortcomings,and not properly controlling for confounding factors.These limitations could potentially misinterpret the impact of environmental exposures and neglect the non-linear association between the outcomes and exposures and the lag effects of exposures.Thus,the reliability of the results cannot be guaranteed in these studies.As the capital of China,Beijing is well populated and developed economically.A comprehensive electronic medical record reporting system is powerful for the collection of data in our study.Beijing has a typical temperate continental monsoon climate,which is representative and has a considerable research significance.As a first-tier city in China,there have been few studies on the health effects of extreme climates in Beijing,yet there is no information on the association between extreme climate events and AMIs.Our work provides theoretical foundation for the establishment of Beijing's public health decision-making,disease prevention and control,meteorological early warning systems,and ultimately reducing the health and economic burden caused by climate change to society.ObjectiveThis study investigated the effects of cold spells,heat waves and extreme humidity on the hospitalizations of AMIs in Beijing,including:(1)To explore the differences between the single-day lag effects and cumulative lag effects of cold spells and heat waves under various definitions,and to explore the optimal definition of cold spells and heat waves in Beijing by model fittings of various definitions;(2)Under the optimal definition of cold spell and heat wave,to evaluate their hysteresis effects and the cumulative effects quantitatively,and to explore the susceptible population;(3)To explore the hysteresis effects and effects accumulation of extreme humidity on AMIs under different humidity indexes and to assess the cumulative effects of extreme humidity on AMI quantitatively.MethodsWe adopted time series study design.We collected and organize the electronic medical records of AMI patients in Beijing from January 1,2012 to December 31,2016.We also collected the daily average temperature(Tmean),daily mean relative humidity(RHmean),daily maximum relative humidity(RHmax),daily minimum relative humidity(RHmin),daily average air pressure(APmean)and other meteorological data.Air Quality Index(AQI)data was obtained from the Beijing Environmental Protection Bureau at the same time.A distributed lag model(DLM)with quasi-Poisson regression was applied to evaluate the lagging and cumulative effects of cold spells and heat waves under different definitions on hospitalizations for AMIs.Gender and age-stratified analysis were conducted to estimate the risks of cold spells and heat waves under each definition.According to the effects of the cold spells and heat waves under different definitions and the results of model fitting,the optimal definition of cold spells and heat waves in Beijing were determined.Under the optimal definition of cold spell and heat wave,we calculated the excess risk and cumulative excess risk of AMI hospitalizations caused by cold spell and heat wave,respectively,and explored the susceptible population under the optimal definition.A distributed lag non-linear model(DLNM)was used to explore the effects of different humidity indicators(RHmean,RHmax,RHmin)on AMI hospitalizations.In order to investigate the differences between effects of extreme low humidity and extreme high humidity on AMI hospitalizations,the 1st percentile,the 10th percentile,the 90th percentile,and the 99th percentile of the humidity index were selected to quantitatively evaluate the cumulative effects of the humidity indicators.In order to study the susceptible population of humidity,the hysteresis effects and cumulative effects of humidity were analyzed in different age groups and different gender groups.ResultsBoth cold spells and heat waves can increase the risk of AMI hospitalizations in the general population,with noticeable lag effects.The effects were different with genders and ages.For cold waves,under the optimal definition(days when daily mean temperature below the 5th percentile for at least 2 consecutive days of the study period),we did not find an increased risk in all the population and various subgroups on the day of cold waves.However they significantly increase hospitalizations 3 to 16 days after the initial exposure.The 21-day cumulative risk of cold spells on AMIs in the general population was increased by 28.6%(95%CI:11.8%-47.8%)compared with the non-cold spell period.For heat waves,the optimal definition was when daily mean temperature above the 90th percentile for at least 2 consecutive days of the study period,and they lead to a 1.6%(95%CI:0.1%-3%)increased risk of AMIs on the day of occurrence compared with the non-heat wave period.The cumulative risks for the general population increased by 21.9%(95%CI:10.1%-35%)for 21 days after exposure.The biggest single-day effect of cold spell on women was greater than that of men.People over 65 and males were sensitive to cold spells and heat waves.We found that both extremely low and high humidity can increase the risk of AMI hospitalizations for the general population.The sensitivity of the indicators to different populations varied.The RHmean at the 1st percentile can cause an increase of 28.6%in the cumulative risk for the total population,and neither RHmin nor RHmax was associated with increased risk of AMIs caused by low humidity.The 90th percentile of RHmean can lead to an increase of cumulative risk of 15.21%in lag 0-21 days,and the effect value increased when the humidity further increased.The RHmean at the 99th percentile can increase the cumulative risk by 23%.Under extremely high humidity,the effects of RHmin on AMIs were greater than the effects of RHmean,and the RHmin at the 99th percentile can cause a cumulative risk increase of 30.5%.Compared with women,humidity caused a higher risk of AMIs in men,and women were only sensitive to extremely low humidity.People over 65 were more susceptible to extreme low humidity.ConclusionCold waves,heat waves,extreme low and high humidity can increase the risk of hospitalizations for AMIs in Beijing.Men and people over 65 years old were sensitive to both cold spells and heat waves.Men were more sensitive to extreme humidity.People over 65 years old were more sensitive to extremely low humidity. |
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