RAPID MEASUREMENT OF SOMATOSENSORY-EVOKED POTENTIAL RESPONSE TO CEREBRAL-ARTERY OCCLUSION

The aim of the paper is to determine the speed of the neurological res ponse to cerebral artery occlusion by monitoring transient changes in somatosensory evoked potentials (SEPs). SEPs, continuously monitored d uring temporary clipping of the middle cerebral artery (MCA) in anaest hetised cats, are analysed. The SEP signals are modelled by a quasi-pe riodic Fourier series, the coefficients of which are estimated with th e aid of two adaptive least squares estimation algorithms. The energy levels at various harmonics throughout the protocol are obtained direc tly from the filter weights. Noise covariance is estimated from pre-st imulus recording, and the adaptation rate of the algorithm is adjusted sweep-by-sweep to accommodate transient changes in the pre-stimulus n oise level. After the occlusion, a significant decrease (p < 0.05) in SEP amplitude is observed. The change In latency is not statistically significant (p similar or equal to 0.5). The spectral trends show a su dden decline in energy at all harmonics immediately following occlusio n, although when the amplifier bandwidth is changed to 5-1500 Hz (from an initial setting of 30-1500 Hz), the fundamental frequency componen t of the SEP signal shows the greatest responsiveness to injury. The a verage time constant of the decline in amplitude resulting from MCA oc clusion is only 10.6 +/- 4.0 s. It is concluded that rapid detection o f cerebral artery occlusion and ischaemia may be feasible by continuou sly monitoring SEP signals and analysing transient changes in time and frequency domains.