Embargoed until 2025-10-11
Author
Date
2023Type
- Doctoral Thesis
ETH Bibliography
yes
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Abstract
Sleep is undoubtedly one of the most powerful mechanisms of the brain and body to recover. Although humans spend around one third of their life time asleep, only little is known about the specific processes through which sleep promotes overall health and well-being. During the transitions from wakefulness to sleep, and between the main sleep stages rapid-eye movement (REM) and non-REM (NREM) sleep, profound changes occur in brain oscillatory patterns and cardiovascular activity. The autonomic nervous system serves as a key regulator of these cardiovascular changes. While REM sleep is associated with increased sympathetic activity, NREM sleep promotes parasympathetic dominance, allowing the body to rest and recover from potential sympathetic overactivity accumulated during wakefulness. The hallmark oscillations of deep NREM sleep, the slow waves, are hypothesized to guide the proposed beneficial and cardio-protective effects of sleep, however, whether slow waves are functionally involved in cardiovascular function remains unclear.
This PhD thesis aimed to address this research gap by applying the currently most promising method to specifically modulate sleep slow waves - auditory stimulation - and measuring cardiovascular parameters during sleep and postsleep. First, we investigated how different auditory stimulation approaches affect brain oscillatory and cardiovascular dynamics during periods of stimulation. We found a biphasic heart rate response and a temporary increase in blood pressure, likely caused by autonomic activation induced by evoking strongly synchronized slow waves in form of K-complexes. Furthermore, we demonstrated sound volume to have the potential to modulate the brain oscillatory response in a dose-dependent fashion.
Next, we showed a robust improvement of left-ventricular function following one night of rhythmic auditory slow wave stimulation. Importantly, this cardio-beneficial effect was reproduced in a second independent night of slightly lower volume auditory stimulation. These findings suggest that slow waves are functionally involved in enhancing post-sleep cardiac function. Lastly, we explored the potential long-term benefits of auditory stimulation on cardiac autonomic regulation in healthy older participants, considering that aging is the main risk factor for the development of cardiovascular diseases. We observed distinct cardiac autonomic activity among participants who respond weakly and strongly to auditory stimulation. Because of the decreased baseline low slow wave activity levels in weak responders, these autonomic differences might be explained through a weaker subcortio-cortical synchronization ability in this group.
Based on our findings, we propose that auditory stimulation modulates cardiovascular function by evoking K-complexes, which in turn organize brain-autonomic-body fluctuations through their strong brain synchronization potential and activation of central autonomic pathways. These fluctuations in autonomic activity may serve to stabilize the cardiovascular system during sleep and thereby enhance the arterial baroreflex, the body’s primary feedback loop for maintaining a stable blood pressure. Consequently, the enhanced coupling may improve cardiovascular regulation during sleep and increases cardiovascular function the next day. Altogether, the interleaved and bidirectional network of brain and cardiovascular activity during NREM sleep seems to be functionally involved in preserving cardiovascular health.
While this PhD thesis provides first causative evidence of the involvement of sleep slow waves in increasing post-sleep cardiac function, further research is required to fully comprehend the mechanisms driving these favorable effects. Nonetheless, we highlight the potential of sleep stimulation and intervention in the prevention and treatment of cardiovascular diseases and its associated risk factors and thereby contributing to cardiovascular health up throughout the aging process. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000635855Publication status
publishedExternal links
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Publisher
ETH ZurichSubject
SLEEP (NEUROPHYSIOLOGY); Cardiovascular system; Autonomic nervous system (ANS); Slow waves; Auditory stimulationOrganisational unit
03963 - Wenderoth, Nicole / Wenderoth, Nicole
Funding
179795 - Boosting sleep to excel during the day: Elucidating the influence of sleep network dynamics on brain and body health (SNF)
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ETH Bibliography
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