Deep Sleep Benefits Heart; Study Says

According to a new study, stimulating the brain with mild noises when deep asleep improves heart performance dramatically. This research has ramifications not only for cardiovascular disorders, but also for competitive sports, among other things. Sleep is an essential part of human life, with deep sleep being especially important for overall health. During this period of sleep, the brain restores, and the rest of the body appears to renew as well.

Researchers at the University of Zurich and ETH Zurich recently demonstrated that increased deep sleep benefits the cardiovascular system in particular: targeted stimulation with brief tones during deep sleep causes the heart – particularly the left ventricle – to contract and relax more vigorously. As a result, it more efficiently pumps blood into the circulatory system and draws it out again. The left ventricle delivers oxygen-rich arterial blood to the majority of organs, the extremities, and the brain.

The left ventricle is squeezed and wrung out like a wet sponge when the heart contracts. The faster and stronger the wringing action, the more blood enters circulation and the less remains in the heart. This boosts blood flow, which benefits the cardiovascular system.

An interdisciplinary team of heart specialists led by Christian Schmied, Senior Consultant for Cardiology at the University Hospital Zurich and adjunct professor at the University of Zurich, used echocardiography (cardiac ultrasound examinations) to show that nocturnal stimulation causes more intense deformation of the left ventricle. This is the first time that an increase in brain waves during deep sleep (slow waves) has been proven to improve heart function. The corresponding study was published recently in the European Heart Journal.

“We anticipated that tonal stimulation during deep sleep would have an effect on the cardiovascular system.” “However, the fact that this effect was so clearly measurable after only one night of stimulation surprised us,” comments project leader and sleep expert Caroline Lustenberger, SNSF Ambizione Fellow at ETH Zurich’s Neural Control of Movement Lab.

Schmied, a heart specialist, is also ecstatic: “We clearly saw that both the heart’s pumping force and its relaxation were greater after nights with stimulation compared to nights without stimulation.” Both are strong indicators of cardiovascular system function.

Pink noise stimulation
The study included 18 healthy men aged 30 to 57 who stayed in the sleep laboratory for three non-consecutive nights. The researchers stimulated the subjects with sounds on two nights and did not on the third.

The scientists continually measured the participants’ brain activity, blood pressure, and heart activity while they slept. They linked their readings to a computer system, which analyzed the data.

When the data indicated that the individual was in deep sleep, the computer played a sequence of very brief tones at specific frequencies, known as pink noise, that sounded like static. Ten seconds of such tones were followed by ten seconds of silence before repeating the procedure. A feedback mechanism ensured that the noise was played at the appropriate time and then ceased, depending on the brain wave pattern.

The researchers were able to directly monitor whether the sound simulation improved deep sleep and altered the individuals’ heart rate and blood pressure using this experimental setting. 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,” lead author Stephanie Huwiler said of the direct impacts during sleep.

The following morning, the heart specialists used echocardiography (ultrasound) to assess the participants’ cardiac function.

Despite the limited group size, significant findings were obtained

“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,” Lustenberger says.

A small group size is typical for laboratory sleep studies, she adds, because they require a lot of resources. In addition, the researchers deliberately selected only men. This is because they are more homogeneous as a group of subjects than women in a comparable age bracket, whose menstrual cycle or menopause has a major effect on their sleep. “When all you’ve got to work with is one night a week for three weeks, the effects of the menstrual cycle will play a role in women. These effects might have masked the stimulation effect in this sort of initial study,” Lustenberger explains.

She cautions, however, that future research must include women, as gender variations in sleep and cardiovascular health are becoming more apparent and have significant implications for primary care.

Future practical advantages

This research is of significant interest not only to cardiologists, but also to athletes. This type of deep sleep stimulation system may enable improved cardiac function in the future – and possibly ensure faster and better recovery after intense workouts,” says Huwiler, who presented the preliminary findings of the study at the Zurich Symposium for Sports Cardiology in March 2023. “The treatment of cardiovascular diseases may be enhanced with this or similar stimulation methods,” Lustenberger adds. However, it is critical to first determine whether patients can benefit from this type of deep sleep stimulation technique.”

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