Search

Differential diagnosis of syncope and seizures frequently imposes a major problem, particularly if interictal examinations are normal. We performed orthostatic testing combined with surface electroencephalography (EEG) and non-invasive measurements of cerebral blood flow velocity. Ten healthy controls, ten patients with confirmed diagnosis of epilepsy and 25 patients with history of syncope of unknown origin were examined. The following parameters were evaluated continuously and simultaneously during orthostatic challenge: computerized EEG with synchronous video-monitoring, transcranial Doppler sonography (TCD), heart rate and blood pressure. Isolated cerebrovascular dysregulation (i.e. a drop in cerebral perfusion despite the absence of a significant drop in peripheral blood pressure) occurred in 2/10 controls, 3/10 patients with epilepsy and 11/25 patients with syncope of unknown origin. The combined EEG and TCD measurements represent a new approach to the work-up of patients with otherwise unexplained syncope, helping us to understand the interdependence of neuronal activity and peripheral/cerebrovascular autoregulation under postural stress.

On the basis of 20 cases in the winter half year, it is found that a southerly low-level jet (LLJ) is regularly associated with extratropical cyclones in the southwestern Great Plains. Only very weak and short-lived lows are not associated with an LLJ. A composite model is constructed that shows the typical sequence of events during the formation of the LLJ in the Texas-Colorado area. This jet is initially dry since it develops over the continent. Only in the advanced stage (1–2 days after its inception), and as it expands over a wide area, does the LLJ start drawing water vapor from the Gulf of Mexico.