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Abstract

Introduction: We have previously studied the relationship of aneurysmal subarachnoid hemorrhage (aSAH) incidence to seasonal and recent temperature changes in 1,168 incident aSAH observed over 2 decades. We found increasing relative risk of aSAH with colder temperatures and temperature drops primarily occurring in cold seasons. Understanding the relationship of incident aSAH to hotter temperatures in which the ambient outside maximum temperature (Tmax) is greater than 70° F will help predict aSAH incidence and lend insight into the pathophysiology of aSAH. Methods: Review of prospectively collected data of incidence aSAH patients admitted to our institution between 1991 and 2009, using hottest months and days during the year in which Tmax > 70° F. We investigated absolute Tmax, average daily temperatures, intraday temperature ranges, and variation of daily Tmax, relative to temperatures greater than 70° F, to assess associations with incidence aSAH. Results: For all days recorded regardless of Tmax, the mean Tmax was lower when aSAH occurred than when it did not (64.4 ± 18.2° F vs. 65.8 ± 18.3° F, p=0.016). During summer months, the odds ratio of incident aSAH increased with lower mean Tmax (OR 1.010, 95% CI 1.001-1.037, p=0.043). The proportion of days with aSAH admissions was lower on hotter days than the proportion of days with no aSAH (96% vs. 98%, P=0.006). Incidence of aSAH during the summer was more likely on days with a temperature fluctuation less than10° F (8% vs. 4%, p=0.002). Conclusions: During the hottest months of the year in the mid-Atlantic region, colder absolute daily maximum temperatures, a smaller heat burden above 70°F and smaller intraday temperature fluctuations are associated with increased aSAH admissions in a similar manner to colder months. These findings bolster the hypothesis that aSAH is more likely with drops in temperature to lower Tmax, lower average daily temperature, even in warmer months. These findings may assist in the development of new prediction models for aSAH based on temperature.