Diurnal Temperature Range as a Risk Factor for Ischemic Stroke Severity in Summer

Abstract

Introduction: Temperature affects human health. It is widely known that mean ambient temperature with both short-term and cumulative lagged effect, is the exposure measure for ischemic stroke. Recently, not only mean temperature, larger diurnal temperature range (DTR, difference between high- and low-daily temperature) was associated with coronary heart disease mortality and ischemic stroke hospitalizations. We hypothesized that a larger DTR results in environmental stress to the human cardiovascular system, thereby increasing the risk for acute ischemic stroke severity. Methods: We used both time-series and case-crossover approaches to assess the relation between DTR and ischemic stroke severity between summer of 2016 and 2018 in Korea. Data were obtained from Korean Stroke Registry and Korean Meteorological Administration. We used exposures averaged over periods varying from 1 to 14 days to assess the effects of DTR on stroke severity. We estimated the relation between DTR and ischemic stroke severity after adjustment for classical stroke risk factor and weather conditions of stroke index day. Results: A 9,249 patients were included in both time-series and case-crossover analyses. The results showed that DTR was significantly associated with stroke severity. The lag effect of DTR was stabilized at about 3-4 days. A 5 °C increase of three-day moving average of DTR corresponded to a 1.67 (95% Confidential Interval, CI 1.64-1.70, p<0.001) and a 5°C increase of DTR of stroke onset day corresponded to a 1.09 (95% CI 1.07-1.12, p<0.001) increase of NIHSS with unidirectional case-crossover analysis after adjustment for classical stroke risk factor and meteorological factor. Discussion: The current study supported our hypothesis that diurnal temperature variation could be a new severity factor for acute ischemic stroke. Moreover, the two different methods we used provided relatively similar results, suggesting that the association between DTR and stroke severity was reasonably robust. Our data added additional evidence that exposure to large DTR was associated with increased burden of stroke. This findings would contribute public health program to prevent unstable thermal environments.