Clinically relevant hand held two lead EEG device

Abstract

A preliminary device has been designed that records a two lead EEG and displays the average signal frequency over a 60 second period. The device is portable and battery operated and has clinical relevance. Between 10% and 40% of hospitalized elderly patients and up to 40% of patients admitted to intensive care units have or develop delirium, a mental state of confusion which often indicates an underlying metabolic, infectious, or other potentially serious but often treatable condition. Despite its potentially serious outcome, the diagnosis of delirium is frequently missed. Fortunately the EEG is a rapid and sensitive test for detecting delirium. The EEG can also indicate the presence of potentially treatable causes of or contributions to dementia, including thyroid disease, malnutrition, infectious disease, or adverse effects from medications. Finding a normal EEG in a patient with suspected delirium or dementia reduces the need for additional costly and potentially risky tests. However, scheduling a full EEG test is time-consuming and expensive, and the results are not usually available in many centers for days or weeks. This portable EEG device can be used by the clinician to rapidly indicate if the patient's EEG is normal or abnormal and if an extensive medical evaluation is warranted. In the present design three electrodes are placed on the scalp with one being a reference electrode that is from a "driven right leg" circuit. The first stage includes radio frequency suppression and protection of the circuit from large voltages possible caused by electrostatic discharges or defibrillation. Next is an instrumentation amplifier with moderate gain followed by other high gain amplifiers. A fifth-order Butterworth low-pass filter is used to suppress frequencies above 30 Hz. The 10 bit A/D converter of a PIC16F88 microcontroller digitizes the signal. The microcontroller uses a C program to determine the average EEG frequency. This result is displayed via a LCD and is updated every 1 minute supplying valuable information to the clinician. © 2010 Springer-Verlag.