The Effect Of Temperature And Relative Humidity On Outpatient Visits Of Circulatory System Disease In Summer

BackgroundClimate has been changing globally,with risen temperature,changed precipitation patterns and increased frequency of extreme weather events.Human health is sensitive to climate change and climate change can affect individual’s health directly or indirectly.The impact of climate change on human health has been studied for a long time.Extreme weather events,as well as adverse weather and environment conditions can increase the risk of mortality,help the spread of infectious diseases and affect the development of chronic non-communicable diseases.With the acceleration of urbanization and population aging,chronic non-communicable diseases have become one of the major health problems in the world,and circulatory system diseases account for a large proportion of chronic non-communicable diseases,including hypertension,cerebrovascular diseases and heart diseases.Studies have shown that extreme high temperature and low temperature can increase the occurrences and mortalities of circulatory system diseases,and other meteorological factors such as air pressure,relative humidity and diurnal temperature range can also affect the developments of circulatory system diseases.Temperature can affect circulatory system by influencing body fluid loss,blood volume and other factors,while relative humidity can affect the body’s sensation of heat to increase or decrease the effect of temperature.The purpose of this study is to investigate the effects of temperature and relative humidity on outpatient visits of circulatory system disease in summer,and explore the impacts of weather conditions that extreme temperatures and relative humidity occur simultaneously,and then,to provide scientific supports for the prevention of circulatory system disease and rational allocation of medical resources.Objectives1.To quantitatively analyze the effects of temperature and relative humidity on outpatient visits of circulatory system disease respectively in summer,and to determine populations vulnerable to temperature and relative humidity.2.To explore the impact of weather conditions that extreme temperatures and relative humidity occur simultaneously,and determine the sensitive circulatory system diseases.MethodsThe meteorological data of this study was obtained from the China Meteorological Data Network.The data of outpatient cases was obtained from the electronic medical records system of the Third People’s Hospital of Cangnan County in Zhejiang Province.We defined different temperature-humidity conditions according to the 25th percentile and the 75th percentile of temperature and relative humidity.We selected patients with circulatory system disease from all outpatient cases according to International Classification of Diseases.Study period was determined by monthly average temperature.Pie graphs and bar graphs were used to describe the meteorological factors and outpatient visits of circulatory system disease,and Spearman correlation analysis was used to explore the correlations between meteorological factors.We established distributed lag nonlinear models using time series meteorological data and outpatient visit date,to explore the effects of temperature and relative humidity on the outpatient visits of circulatory system diseases during 7 lag days.In DLNM analysis,we chose meteorological factors whose correlation coefficient with temperature and relative humidity was less than 0.5as confounders,and determined the degrees of freedom according to existed literatures and Akaike Information Criterion.We also preformed subgroup analysis in terms of gender,age and disease types.Meanwhile,we conducted a time stratified case-crossover study using meteorological data and outpatient cases data,with the usage of conditional Logistic model,to explore the effects of different temperature-humidity conditions during 7 lag days.This analysis can control long-term trend and the effect of day of week by study design.The meteorological confounders in DLNM analysis was controlled in Logistic regression.We also performed subgroup analysis in terms of disease types.Results1.In 2010-2013,the months with highest average temperature were July,August and September,so we selected July to September,2010-2013 as study period.During this period,the average temperature of Cangnan County was 28.03℃,and the average relative humidity was 75.48%.The condition of low temperature together with low humidity accounted for 8.97%of the whole study period.The condition of low temperature together with high humidity accounted for 11.14%.The condition of high temperature together with low humidity accounted for 11.96%.There was no condition of high temperature together with high humidity during study period.2.In the summer of 2010-2013,the outpatient visits of circulatory system disease of the Third People’s Hospital of Cangnan County was 9990.Males accounted for 56.59%of all circulatory system disease cases;females accounted for 43.31%;patients aged 0-14 accounted for 0.87%;patients aged 15-29 accounted for 2.98%;patients aged 30-44 accounted for 16.21%;patients aged 45-59 accounted for 24.80%;patients aged 60-74 accounted for 39.00%;patients older than 74 years old accounted for 16.14%;patients with hypertension accounted for 61.00%;patients with cerebrovascular disease accounted for 18.60%;patients with heart disease accounted for 11.01%;patients with peripheral vascular and lymphatic disease accounted for 9.08%.Apart from the group of heart disease,the largest outpatient visits occurred at September in other groups.3.In summer,the effect of temperature on the outpatient visits of circulatory system disease was nonlinear with lag effect.The effects of temperature for people aged 0-44 and people aged 45-59 were statistically significant.For the people aged 0-44,the outpatient visits of circulatory system disease increased when the temperature was 21.9℃-24.7 and 29.8-32.2℃.The largest separate effect occurred when the temperature was 22.4℃ on lag 0.For the people aged 45-59,the outpatient visits increased when the temperature was 19.7℃-27.2℃.The largest separate effect occurred when the temperature was 19.7℃ on lag 7.4.In summer,the effect of relative humidity on the outpatient visits of circulatory system disease was nonlinear with lag effect.For all circulatory system disease,the outpatient visits increased when the relative humidity was 76.1%-92.0%.The largest separate effect occurred when the relative humidity was 92.0%on lag 2.The effects of relative humidity in different subgroups were inconsistent.For male,people aged 45-49,people older than 74 and patients with hypertension,the largest separate effects occurred at the maximum relative humidity,while for people aged 0-44,people older than 74 and patients with cerebrovascular disease,the largest separate effects occurred at the minimum relative humidity.5.The effects of temperature-humidity conditions differed in groups with different circulatory system diseases.The condition of low temperature together with low humidity can increase the outpatient visits of cerebrovascular disease on lag 5.The conditions of low temperature together with high humidity can increase the outpatient visits of hypertension,cerebrovascular disease and heart disease,respectively on lag 2,4,lag 7 and lag 3.However,the conditions of high temperature together with low humidity can decrease the outpatient visits of hypertension,heart disease,peripheral vascular and lymphatic disease.Conclusions1.In summer,temperature can affect the outpatient visits of circulatory system disease.High temperature can increase the visits in people younger than 45 years old.Low temperature can increase the visits in people younger than 60 years old.So when extreme temperature condition occurs in summer,people should take measures to prevent the development of circulatory system diseases,for example,adjusting the labor intensity and optimize the working environment to reduce the burden on the circulatory system.2.In summer,relative humidity can affect the outpatient visits of circulatory system disease.High relative humidity can increase the visits in whole population,male,people aged 45-59,people older than 74 and patients with hypertension,while low relative humidity can increase the visits in people aged in 0-44,people older than 74 and patients with cerebrovascular disease.The prevention in extreme humidity condition is as important as temperature.In extreme humidity condition,people should take measures,for example,drinking enough water timely to maintain water-salt balance in body,to reduce the risk of circulatory system disease.3.When extreme temperature and humidity occur simultaneously,the effect is much more adverse than they occur separately.For different types of circulatory system disease,the conditions of low temperature together with low humidity can increase the risk of cerebrovascular disease,and the condition of low temperature together with high humidity can increase the risk of hypertension,cerebrovascular disease and heart disease.Therefore,when extreme temperature and humidity occur simultaneously,we should take measures to prevent the development of circulatory system disease.Specifically,in cool weather in summer,high and low humidity both can increase the risk of circulatory system disease,so the public should pay more attention to sudden changes in atmospheric environment in summer.