| The brain is critically dependent on blood flow and oxygen supply for its normal function. Few existing methods allow rapid non-invasive assessment during critical hypoxic events. A novel technique for recording and analyzing brain auditory evoked potential (BAEP) under hypoxic conditions was developed. Experiments were performed on a healthy subject during hyperventilation (HV) and episodes of periodic breath-holding. Surface electrodes were used to measure EEG (electro-encephalogram) and also BAEP in A2-Cz configuration. Auditory stimuli were applied in the form of 0.1 seconds stream of clicks. An analog circuit and data acquisition system was developed for amplifying, filtering and recording the EEG from Cz-A2 position. Data were digitized online. Signal processing techniques were performed to extract and analyze BAEP using Latency Correction (LC), Ensemble Averaging, Continuous Wavelet Transform (CWT), and Principal Component Analysis (PCA). Results showed that the hypoxic conditions caused depolarization and hyperpolarization, producing aggregate potentials or field potentials. BAEPs can be extracted and analyzed under hypoxic conditions with minimum averaging (400 realizations) allowing real time evaluation of the auditory pathway. Increased activity in the auditory pathway directly following depletion of oxygen to the brain was observed. The hypoxic condition was confirmed when BAEP was used in combination with a near-infrared spectroscopic device for quantifying oxygenation. Thus, the BAEP system designed here can be used for non-invasive, real-time assessment of the auditory pathway, in identifying abnormal breathing and hypoxic events, and in the evaluation of patients suffering from cerebrospinal injury when used in conjunction with near-infrared oxygenation monitoring system. |
