Deep sleep stimulation can improve cardiac function overnight

A recent study highlights the importance of deep sleep for cardiovascular health. 

The research provides valuable insights into how targeted stimulation during deep sleep can substantially benefit the heart, particularly the left ventricle, optimizing its functionality to pump and extract blood more efficiently. 

Such enhanced activity in the left ventricle subsequently improves the supply of oxygen-rich arterial blood to vital organs, extremities, and the brain.

How the research was conducted 

The study was led by Christian Schmied, Senior Consultant for Cardiology at the University Hospital Zurich. 

The researchers used auditory stimulation to experimentally enhance slow waves. Using echocardiography, the experts obtained visual images of the heart to demonstrate that nocturnal stimulation intensifies the deformation of the left ventricle. 

Improved cardiac function 

Through their examination, the researchers observed that an increase in brain waves during deep sleep (slow waves) directly correlated with improved cardiac function.

“We were expecting that stimulation with tones during deep sleep would impact the cardiovascular system. But the fact that this effect was so clearly measurable after just one night of stimulation surprised us,” explained project leader Caroline Lustenberger, a sleep expert at ETH Zurich.

“We clearly saw that both the heart’s pumping force and its relaxation were greater after nights with stimulation compared to nights without stimulation,” said Schmied. Both factors are an excellent measure of cardiovascular system function.

Focus of the study

The study was focused on 18 healthy male participants between the ages of 30 and 57. Over three non-consecutive nights, the subjects were closely monitored while they slept, with the research team employing sound stimulation on two nights and abstaining on the third. 

This precise approach offered researchers an opportunity to directly observe the correlation between sound stimulation-enhanced deep sleep, and the participants’ heart rate and blood pressure.

Continuous measurements 

A computer system was used to meticulously analyze data from continuous measurements of the subjects’ brain activity, blood pressure, and heart activity during sleep. 

The system played a series of brief tones, or “pink noise,” upon detecting that a subject had entered deep sleep. This experimental design allowed the team to monitor the immediate effects of sound stimulation on deep sleep and the cardiovascular system.

Increase in slow waves

“During stimulation, we clearly see an increase in slow waves, as well as a response from the cardiovascular system that is reminiscent of cardiovascular pulsation,” said study lead author Stephanie Huwiler.

“Despite the relatively small group of subjects, the results are significant. We were also able to reproduce the results on two separate nights, which in statistical terms makes them very strong,” said Lustenberger.

Study implications 

According to Huwiler, the deep sleep stimulation system developed in this study could have valuable applications in preventive medicine and competitive sports. 

“Especially in preventive medicine, but also in competitive sport, this kind of deep sleep stimulation system might enable improved cardiac function in the future – and possibly ensure faster and better recovery after intense workouts,” said Huwiler.

“The treatment of cardiovascular diseases may be enhanced with this or similar stimulation methods,” said Lustenberger. “However, it’s crucial to first investigate whether patients can benefit from this kind of deep sleep stimulation method as well.”

The research is published in the European Heart Journal.

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