Scientists used "pink noise" to stimulate the brain during deep sleep and discovered it boosted cardiovascular function.
In 2022, the American Heart Association added sleep to its cardiovascular health checklist after reviewing volumes of research on the links between healthy sleep and heart health. The updated Life's Essential 8 suggests that people should get seven to nine hours of sleep daily for maximum cardiovascular benefits.
Though scientists and health experts understand the importance of healthy sleep for heart health and overall well-being, researchers from ETH Zurich and the University of Zurich wanted to determine if specific brain waves associated with deep sleep impacted cardiovascular function.
Published in the European Heart Journal on October 5, the study recruited 18 male participants aged 30 to 57 who were non-smokers and had no cardiovascular disease, sleep disorders, or other conditions that could impact sleep.
The team selected males because female participants could experience sleep issues due to menopause or the menstrual cycle, which might skew the results.
During the three-night experiment, the participants slept while wearing a deep sleep stimulation system. Once they fell asleep, the researchers stimulated the participants with specific sounds called "pink noise" for two out of the three nights.
Pink noise consists of auditory tones at specific frequencies that sound similar to static. During sleep, the participants heard ten seconds of these tones, followed by ten seconds of silence. This cycle repeated depending on brain wave patterns.
The team was able to monitor whether the sound simulation enhanced deep sleep and if it affected the participants' blood pressure and heart rate.
After the participants awakened, they underwent echocardiography to determine the cardiovascular effects of the auditory stimulation.
The team found that stimulation with brief auditory tones during deep sleep causes the heart – especially the left ventricle – to function more effectively. This, in turn, increases blood flow to the brain, organs, and extremities.
"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 Christian Schmied, a senior consultant for cardiology at the University Hospital Zurich, in a news release.
The study's authors say this is the first time a research team has found that increased slow brain waves during deep sleep improve heart function.
Moreover, the team could also reproduce the results on two separate nights, which is statistically significant.
The authors explain that because sleep quality can impact athletic performance, these findings may also interest athletes.
"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," says Stephanie Huwiler of the Department of Health Sciences and Technology at ETH Zurich.
Though the study used a small number of participants, the authors say a small group size is typical for laboratory sleep studies because they require significant resources. In addition, because the research only included male participants, the scientists say future studies should include females to determine if these deep sleep heart benefits also occur in women.
- European Heart Journal. Auditory stimulation of sleep slow waves enhances left ventricular function in humans.
- ETH Zurich. Increased deep sleep benefits your heart.