Most investigations linking sleep and cardiovascular health focus on sleep duration or sleep efficiency. ETH Zurich focused on brain activity.

By Alyx Arnett

Key Facts:

  • A proof-of-concept study conducted on middle-aged male participants explored the impact of auditory stimulation on sleep slow wave activity and whether it affects cardiovascular function during and after sleep.
  • They found auditory stimulation significantly increased slow wave activity. The increase correlated with improved functioning of the left ventricle of the heart.
  • The research suggests that consolidated and deep NREM sleep, not just sleep duration or sleep efficiency, promotes cardiovascular health.  
  • Sleep slow wave stimulation should be explored as an adjunctive therapeutic approach in managing cardiovascular diseases. 

A recent study suggests that targeted auditory stimulation of slow waves in the brain, occurring during non-rapid eye movement (NREM) sleep, could unlock new treatments for cardiovascular diseases.

Caroline Lustenberger, PhD, (left) and Stephanie Huwiler (right) of ETH Zurich

The double-blind, cross-over trial, involving 18 healthy male participants explored the impact of auditory stimulation on slow wave activity and whether it affects cardiovascular function during and after sleep. In a sleep lab, bursts of pink noise—each one second apart—were delivered in a windowed 10 seconds “on” followed by 10 seconds “off” for four hours.  

This auditory stimulation significantly increased slow wave activity, and, more importantly, this increase correlated with improved functioning of the left ventricle of the heart, a key chamber responsible for pumping oxygenated blood throughout the body.

The researchers say this discovery opens up new perspectives on how sleep quality, not just duration, can be a critical factor in maintaining and potentially improving heart health.

First author Stephanie Huwiler, a PhD candidate in the Neural Control of Movement Lab, Institute of Human Movement Sciences and Sport, Department of Health Sciences and Technology at ETH Zurich, and corresponding last author Caroline Lustenberger, PhD, junior group leader of the Neural Control of Movement Lab, discussed the study with Sleep Review over email.

[Editor’s Note: Read the study, “Auditory stimulation of sleep slow waves enhances left ventricular function in humans,” in European Heart Journal.]

What inspired you to explore the relationship between auditory stimulation of sleep slow waves and cardiovascular function?

Sleep research, primarily rooted in neuroscience, has traditionally been centered on the brain. However, it’s crucial to understand that the brain doesn’t function in isolation from the body. 

Over recent decades, there’s been a growing interest in the role of sleep in supporting overall bodily health. Of particular note is cardiovascular health, given its significance in ensuring longevity, especially considering cardiovascular diseases represent the leading cause of death worldwide. 

A growing body of evidence suggests a correlation between poor sleep, mainly tied to sleep duration, and an increased likelihood of developing risk factors for cardiovascular diseases. This includes conditions such as hypertension, dyslipidemia, and obesity. Other studies have indicated that during deep sleep, marked by prevailing slow waves, the cardiovascular system enters a state of enhanced rest. However, the specific sleep mechanisms contributing to cardiovascular function remain elusive. Consequently, our research seeks to determine the potential role of slow waves in enhancing cardiovascular function and health.

What were the main findings of your study?

We found that auditory stimulation in healthy male participants significantly enhanced slow wave activity and influenced immediate cardiovascular dynamics when stimulation was applied. 

Moreover, we observed significant post-sleep changes in echocardiographic parameters, indicating enhanced left-ventricular diastolic and systolic function compared to the sham night. Systolic function reflects the contractility of the heart when blood gets ejected to the body, and diastolic function reflects the relaxation of the ventricle when it is filled up again with blood.

We applied two sound volumes of auditory stimulation but did not observe a clear dose dependency in the effect compared to a control night, where no tones were applied. We observed similar changes after both stimulation nights, indicating a robustness in the effect on post-sleep cardiac function.

Were there any surprising results?

For a long time, slow wave sleep was considered to be a period of cardiovascular quiescence, indicated by the lowest blood pressure and heart rate. This quiescence most likely results from predominance of the parasympathetic nervous system, which is the rest-promoting branch of the autonomic nervous system. 

In our study, we observed that an increase in slow waves through auditory stimulation induces a bi-phasic heart rate response (acceleration followed by deceleration) and a transient increase in blood pressure. This cardiovascular activation response that resembles cardiovascular pulsations surprised us.

How might these findings enhance our understanding of sleep’s role in cardiovascular health?

We provided evidence that slow waves are functionally involved in enhancing cardiac function. Therefore, this represents an essential step towards emphasizing sleep as an important pillar for overall health. Sleep was added last year to the Life’s Essential 8 of the American Heart Association, representing the eight most important modifiable factors for promoting cardiovascular health. 

Nevertheless, a strong focus is still paid to sleep duration only. But sleep is a very dynamic process, and sleep duration does not necessarily imply sleep quality. With our research, we shed light on the importance of slow waves and, therefore, consolidated and deep NREM sleep, being involved in promoting cardiovascular health.  

What are the potential therapeutic applications of sleep slow wave stimulation?

Our research underscores the beneficial effects of deep NREM sleep in bolstering cardiac function, spotlighting the vital role of slow waves in maintaining cardiovascular health. Given the limited therapeutic options for diseases, particularly those tied to reduced left-ventricular diastolic function, any supplementary treatment could be invaluable for affected patients. 

Our findings advocate for exploring sleep slow wave stimulation as an adjunctive therapeutic approach in managing cardiovascular diseases. Additionally, this method might offer a means to boost cardiovascular health and recovery in athletes

Nevertheless, it’s crucial to emphasize the need for further research, both broadly and within these potential target demographics, before endorsing the therapeutic applications of sleep slow wave stimulation.

How does your work add to previous studies on sleep and heart health?

Previous studies were mostly correlative and frequently only considered sleep duration or sleep efficiency as a marker for sleep. We disentangled specifically the role of sleep slow waves in promoting cardiac function. 

Are there elements of this research that might inform current practices in sleep medicine?

Our research underscores the importance of the quality of sleep, specifically the role of slow waves during NREM sleep, in cardiovascular function. This adds a new dimension to sleep medicine, suggesting that focusing on enhancing slow wave activity could be beneficial. 

The observed cardiovascular dynamics during slow wave stimulation also offer a fresh perspective on sleep’s intricate relationship with heart health. These insights can inspire a more comprehensive approach to sleep medicine, encompassing both the depth and duration of sleep for optimal health outcomes.

What future research should be done?

Our research serves as a proof-of-concept study conducted on middle-aged male participants. It’s crucial to extend our research to include females, older individuals, and larger-scale studies with a more diverse set of participants. Both the health implications and the potential benefits for athletes, especially regarding recovery, are intriguing. 

Moreover, it’s essential to assess the feasibility of slow wave stimulation for individuals with health conditions and determine its long-term effects. In our future endeavors, we aim to diversify stimulation techniques and settings to pinpoint the most effective interventions for optimal sleep and health outcomes.

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