Session S22.2

Dynamic Cardiovagal Response to Motion Sickness: A Point-Process Heart Rate Variability Study

L LaCount*, V Napadow, B Kuo, K Park,
J Kim, E Brown, R Barbieri

Center for Biomedical Imaging
Charlestown, MA, USA

Nausea is a commonly occurring symptom typified by strong visceral response and generalized discomfort. It can arise from a variety of causes including as a side effect of pharmacotherapy and general anesthesia, pregnancy, and visual/vestibular sensory discordance ("motion sickness"). In this study, a visual display of stripes was used to examine the response of the autonomic nervous system to motion sickness. Heart rate variability was investigated using dynamic methods to discern instantaneous fluctuations in reaction to stimulus or perception-based events. ECG and skin conductance were recorded from 10 female subjects lying supine. Subjects rested with their eyes open for five minutes before and after the stimulus, which was presented for 20 minutes or until severe nausea was reported, and rated their level of nausea on a scale from “0” (no nausea) to “4” (severe nausea). ECG was collected at 400 Hz, and R-R interval obtained through automated methods with manual adjustments. A novel point process adaptive recursive algorithm was applied to R-R series to compute instantaneous mean heart rate, heart rate variability, and high frequency power (HF, 0.15-0.5 Hz) as a marker of vagal activity. Sub-segments with constant nausea level were considered for stationary analysis, whereas non-stationary trends were assessed using windows from 30 seconds before to 60 seconds following events of interest. These events included the beginning of the nausea stimulus, increases in rating events, and the end of the nausea stimulus. Paired t-tests were used for all comparisons. Dynamic trends were seen in each subject. Despite high inter-subject variability, HF power averaged across subjects indicated a significant decrease several seconds after the rating changes to “1” (mild nausea). Conversely, right before “3” (strong nausea), the group average shows a trending increase in HF power. While stationary findings confirm a general sympathetic activation with increasing nausea, the instantaneous estimates further provide a novel dynamic characterization capable of discerning transitory increases in vagal tone immediately before the subject reports flushes of strong nausea.

(Abstract Control Number: 139)