A novel quantitative EEG injury measure of global cerebral ischemia.

OBJECTIVE: To develop a novel quantitative EEG (qEEG) based analysis method, cepstral distance (CD) and compare it to spectral distance (SD) in detecting EEG changes related to global ischemia in rats. METHODS: Adult Wistar rats were subjected to asphyxic-cardiac arrest for sham, 1, 3, 5 and 7 min (n=5 per group). The EEG signal was processed and fitted into an autoregressive (AR) model. A pre-injury baseline EEG was compared to selected data segments during asphyxia and recovery. The dissimilarities in the EEG segments were measured using CD and SD. A segment measured was considered abnormal when it exceeded 30% of baseline and its duration was used as the index of injury. A comprehensive Neurodeficit Score (NDS) at 24 h was used to assess outcome and was correlated with CD and SD measures. RESULTS: A higher correlation was found with CD and asphyxia time (r=0.81, P<0.001) compared to SD and asphyxia time (r=0.69, P<0.001). Correlation with cardiac arrest time (MAP<10 mmHg) showed that CD was superior (r=0.71, P<0.001) to SD (r=0.52, P=0.002). CD obtained during global ischemia and 90 min into recovery correlated significantly with NDS at 24 h after injury (Spearman coefficient=-0.83, P<0.005), and was more robust than the traditional SD (Spearman coefficient=-0.63, P<0.005). CONCLUSION: The novel qEEG-based injury index from CD was superior to SD in quantifying early cerebral dysfunction after cardiac arrest and in providing neurological prognosis at 24 h after global ischemia in adult rats. Studying early qEEG changes after asphyxic-cardiac arrest may provide new insights into the injury and recovery process, and present opportunities for therapy.

In vivo nitric oxide sensor using non-conducting polymer-modified carbon fiber.

Nitric oxide (NO) is emerging as a very important and ubiquitous gaseous messenger in the body. The response characteristics of NO sensors made of non-conducting polymer modified carbon fiber electrodes are investigated to determine their selectivity, sensitivity, and stability for in vivo use. A composite polymer, comprising Nafion, m-phenylenediamine, and resorcinol, showed the best selectivity and stability to amperometric NO detection. The non-conducting, self-limiting polymer film protects the electrode from interference and fouling by other biochemicals. Although the relative sensitivity to NO of the modified sensor is lower than that of the unmodified carbon fiber electrodes (less than 6%), the composite polymer electrode showed high selectivity against ascorbic acid (> 2000:1), nitrite (> 600:1), and dopamine (> 200:1). The stability of the NO sensor was maintained for at least 1 week. The NO sensitivity after in vivo experiments (n = 8) is 88.1 +/- 5.6% of initial sensitivity data obtained before in vivo experiments. Preliminary in vivo experiments done with this electrode are shown to capture elevated NO levels in brain following an ischemic injury.