Abstracts

Rationale: Photoplethysmography (PPG) is a technique that uses reflected light waves to detect blood volume pressure changes in body tissue. As these changes reflect variations in cardiovascular indices such as heart rate and vascular tone, PPG may be used to identify autonomic nervous system alterations caused by seizures. The aim of this study is to assess the variability of PPG signals in the pre-ictal period in patients with Focal Impaired Awareness Seizures (FIAS).  Methods: PPG data were recorded using a wrist and ankle band sensor (E4, Empatica Inc., Milan, Italy) worn by patients admitted to the Epilepsy Monitoring Unit at Boston Children’s Hospital between February 2015 and January 2018. EEGs and seizure videos were reviewed by a board certified epileptologist to determine seizure EEG onset and offset, and confirm seizure type. We included FIAS that were separated by at least 90 minutes from other seizures, and selected signals that were free from motion artifacts. Signals were analyzed in two minute portions from three periods: (i) baseline: 5 hours to 30 minutes before seizure onset; (ii) pre-ictal: 5 minutes before seizure onset to seizure onset; (iii) ictal: spanning the total duration of the seizure (iv) post-ictal: seizure offset to 1 hour after seizure offset. We included 4 control portions, from a period 6 hours from any seizure to assess for baseline inter-patient variability. Using Matlab, we derived the Area Under the Curve (AUC) of the PPG signal from each of the studied periods and AUC was compared using linear mixed-effects model. Results: We included 11 patients with a total of 18 FIAS. Patients’ age ranged from 7 to 15 years, and 55% of the study group were females. Pre-ictally, the area under the curve reached 44.89 nW.s (95% CI=36.13-53.66, p<0.001) compared to 35.32 nW.s (95% CI=26.56-44.08, p<0.001) at the baseline. The AUC drops to 19.04 nW.s (95% CI=10.17-27.91, p<0.001) during the seizure and increased again to 37.28 nW.s (95% CI=28.52-46.05, p<0.001) post-ictally. AUC in control portions had an average of 34.29 nW.s (95% CI=21.35-46.8, p<0.001). When we compared the difference in variability among controls, and between controls, baseline and peri-ictal periods we saw a significant and consistent increase in difference that starts in the pre-ictal period, continues to increase throughout the seizure and decreases in the post-ictal period. Conclusions: PPG signals showed significant changes in the pre-ictal period in patients with FIAS. Analysis of the AUC of the PPG signals, showed a consistent increase in difference from baseline in the period five minutes before seizure onset. With more research, PPG may serve as a marker for detection and potentially prediction of FIAS. (Funded by Epilepsy Research Fund) Funding: Epilepsy Research Fund