Autonomic regulation of the cardiovascular system after awakening and motor activity during night sleep under conditions of prolonged isolation: A descriptive study

Introduction. Adequate night sleep is crucial for maintaining health and optimal performance. Under chronic stressors, such as prolonged isolation, sleep quality and duration become critical determinants of resilience: sleep disturbances can exacerbate psychological distress and impair cognitive functioning. In such conditions, sleep duration becomes a crucial factor affecting the well-being and productivity of a human operator on the following day. However, its role in shaping the processes of morning activation has been insufficiently studied.

Objective. To identify the characteristics of motor activity during night sleep and autonomic regulation after morning awakening in individuals with different sleep durations under conditions of a prolonged isolation experiment.

Materials and methods. The study was conducted within the framework of the international isolation experiment “SIRIUS-23/24” and involved six healthy volunteers (two men, four women; age range: 25–37 years). Based on sleep duration, participants were divided into two groups: a short-sleep group (< 7 h; n = 4; two men, two women; aged 27–37) and a longer-sleep group (> 7 h; n = 2; both women; aged 25 and 34). Monthly monitoring of motor activity during sleep was carried out using actigraphy, along with ECG recording and sleep characteristics questionnaires completed immediately after awakening. The following parameters were analyzed: heart rate variability indicators (SDNN, TP, VLF, SI, LF/HF), the Kerdo vegetative index, as well as sleep duration, sleep efficiency, and motor activity during sleep. To assess the significance of differences between the identified groups, the non-parametric Mann–Whitney U test was applied.

Results. Participants in the short-sleep group demonstrated lower sleep efficiency and higher motor activity during nighttime hours. In the same group, a relative reduction in sympathetic influences was observed after awakening, evidenced by lower heart rate values (61.5 bpm, p = 0.049), Kerdo vegetative index (–9.4 arbitrary units, p = 0.015), and SI (48 arbitrary units, p = 0.04). At the same time, parasympathetic activity was enhanced, as shown by higher SDNN (59.3 ms, p = 0.005) and TP (1994 ms², p = 0.006), indicating impaired morning activation. In the long-sleep group, despite better sleep parameters, lower VLF power values were recorded after awakening compared to the short-sleep group (p ≤ 0.05).

Conclusions. Under prolonged isolation conditions, some crew members exhibited short sleep duration (< 7 h), which was associated with increased motor activity during nighttime sleep, reduced sleep efficiency, and attenuated sympathetic regulation of heart rate after awakening. These findings highlight the need for an individualized approach to sleep schedule optimization to maintain performance and health in extreme environments.

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