Heart Rate Variability as a Predictor of Daytime Sleepiness During Prolonged Isolation

The 120-day isolation experiment (SIRIUS-19 program) within the SIRIUS project (http://sirius.imbp.ru/) involved 6 volunteers aged 28 to 44 years (three men and three women). Research methods included daily ECG registration to assess heart rate variability, blood pressure measurement and self-assessment of sleep quality over the past night using a visual analogue scale. The studies were carried out in the morning after waking up. Once a week in the evening (17.00–19.00), volunteers filled out a scale of clinical daytime sleepiness self-assessment, which allows evaluate the subjective condition over the past day. During the regression analysis, the possibility of predicting the appearance of daytime sleepiness in terms of cardiac activity was assessed. It was found, that the heart rate, blood pressure and heart rate variability indicators recorded in the morning time make it possible to measure the quality of past sleep and predict the level of subsequent daytime sleepiness. We assume that the increased activity of the parasympathetic branch of the autonomic nervous system in the morning characterizes both the previous lack of sleep and the risk of developing sleep inertia and daytime sleepiness in general.