Anomalous equivalent potential temperature: an atmospheric feature predicting days with higher risk for fatal outcome in acute ischemic stroke-a preliminary study.

Acute stroke is a life-threatening condition. Fatal outcome is related to risk factors, some of these affected by climatic changes. Forecasting potentially harmful atmospheric processes may therefore be of practical importance in the acute care of stroke patients. We analyzed the history of all patients with acute ischemic stroke (N = 184) confirmed by neuroimaging including those who died (N = 35, 15 males) at our hospital department in the winter months of 2009. Patient data were anonymized, and the human meteorologists were only aware of patients' age, gender, and exact time of death. Of the meteorological parameters, equivalent potential temperature (EPT) has been chosen for analysis. EPT is generally used for forecasting thunderstorms, but in the case of synoptic scale airflow (10(6) m), it is suitable for characterizing the air mass inflowing from different regions. The behavior of measured EPT values was compared to the climatic (30 years) averages. We developed meteorological criteria for anomalous periods of EPT and tested if such periods are associated with higher rate of fatal outcome. The duration of anomalous and non-anomalous periods was nearly equal during the studied 3 months. Stroke onset distributed similarly between anomalous and non-anomalous days; however, of the 35 deaths, 27 occurred during anomalous periods: on average, 0.56 deaths occurred on anomalous days and 0.19 on non-anomalous days. Winter periods meeting the criteria of anomalous EPT may have a significant adverse human-meteorological impact on the outcome in acute ischemic stroke.