Relationship of aneurysmal subarachnoid hemorrhage to changes in atmospheric pressure: results of a prospective study

Object. The purpose of this study was to evaluate the relationship between atmospheric pressure and subarachnoid hemorrhage (SAH) in a region in the English Midlands. Methods. All patients with angiographically proven SAH for the calendar year 1998 were analyzed. A geographical allocation was made based on the patients' origin within the region. The events were then compared with the data available for the local atmospheric pressures. One hundred nine patients had an SAH during the time period studied. The median atmospheric pressure recorded was 1014.5 millibars. Atmospheric pressure was modestly correlated with the number of SAHs per day (Spearman's rank correlation, r = 0.33; p < 0.0001); the daily change in atmospheric pressure also correlated mildly (r = 0.34, p < 0.0001). No other statistically significant association was found. Conclusions. The authors have shown a relationship between high atmospheric pressure and increased incidence of SAH. The underlying reason for this remains obscure.