Sleep is made up of different phases and deep sleep is especially important for health, since our brain recovers during this stage and the rest of the body also seems to regenerate. A new study has shown that more deep sleep particularly benefits the cardiovascular system and that stimulation with short tones (pink noise) during deep sleep causes the heart, specifically the left ventricle, to contract and relax better, which It allows the heart to pump blood into the circulatory system and remove it more efficiently.
The left ventricle supplies oxygen-rich arterial blood to most organs, the extremities, and the brain. When the heart contracts, the left ventricle squeezes and wriggles out like a wet sponge. The more immediate and powerful this draining action is, the more blood enters the circulation and the less remains in the heart. This increases blood flow, which has a positive effect on the cardiovascular system.
The study was carried out by a team of heart specialists from ETH Zurich and the University of Zurich, led by Christian Schmied, senior consultant for cardiology at University Hospital Zurich. Researchers used echocardiography (cardiac ultrasound examinations) to show that the left ventricle undergoes more intense deformation after nocturnal stimulation.
A noticeable improvement in cardiac function
It is the first time that an increase in brain waves during deep sleep (slow waves) has been shown to improve heart function. The findings have been published in the European Heart Journal. “We expected that tone stimulation during deep sleep would affect the cardiovascular system. But the fact that this effect was so clearly measurable after just one night of stimulation surprised us,” explained project leader and sleep expert Caroline Lustenberger, SNSF Ambizione Fellow in the Neural Control of Movement Laboratory at ETH Zurich.
“We have clearly seen that both the pumping force of the heart and its relaxation were greater after nights with stimulation.” [con ruido rosa]”
Schmied was also very satisfied with the results: “We clearly saw that both the pumping force of the heart and its relaxation were greater after the nights with stimulation than during the nights without stimulation. “Both factors are an excellent measure of the function of the cardiovascular system.”
The study involved 18 healthy men between 30 and 57 years old, who spent three non-consecutive nights in the sleep laboratory. For two nights, the researchers stimulated them with sounds and one night they did not. While the individuals slept, the scientists continuously measured their brain activity, blood pressure, and heart activity, and connected their measurements to a computer system that analyzed the input data.
As soon as the readings indicated that the person had fallen into a deep sleep, the computer played a series of very brief tones at certain frequencies, called pink noise, that sound like static. Ten seconds of these tones were followed by 10 seconds of silence, and then the same procedure was repeated. A feedback mechanism ensured that the noise was played at the right time and, depending on the brain wave pattern, stopped again.
This experimental setup allowed the researchers to directly monitor whether the sound simulation improved deep sleep and influenced the subjects’ heart rate and blood pressure. “During stimulation, we clearly see an increase in slow waves, as well as a response of the cardiovascular system reminiscent of cardiovascular pulsation,” says the lead author. Stephanie Huwiler, describing the direct effects during sleep. The next morning, cardiologists examined the participants’ heart function using echocardiography.
Possible applications of pink noise in competitive sports
Although it is a small study, typical of laboratory sleep studies, and only men participated, Lustenberger assures that the results are significant. The researchers purposely only selected men because in the case of women of similar age, other factors such as the menstrual cycle or menopause could have influenced them, but the researcher says that future studies should include women, since gender differences in sleep and cardiovascular health are increasingly evident and have profound implications for primary health care.
This study is of great interest not only for cardiologists but also for athletes. “Especially in preventive medicine, but also in competitive sport, this type of deep sleep stimulation system could make it possible to improve cardiac function in the future and possibly ensure better and faster recovery after intense training,” says Huwiler, who presented the first results of the study at the Zurich Sports Cardiology Symposium in March 2023.
“The treatment of cardiovascular diseases can be improved with this or other similar stimulation methods. However, it is essential to first investigate whether patients can also benefit from this type of deep sleep stimulation method,” concludes Lustenberger.
