Deep sleep, also known as slow-wave sleep, is essential for good health. Not only does it enable physical recovery, it also helps consolidate information learnt during the day, boosts the immune system, and reduces stress levels.
A team of cardiologists from ETH Zurich and the University of Zurich has demonstrated that deep sleep can improve heart function when stimulated with certain sounds.
Published in the European Heart Journal, the study involved 18 healthy men, aged between 30 and 57, who spent three non-consecutive nights in a sleep laboratory. Pink noise was played when the subject fell into a deep sleep, in sequences of 10 seconds at certain frequencies, followed by 10 seconds of silence, for two nights.
The participants were then subjected to no stimulation on the final night. The researchers measured and analysed their brain activity, blood pressure and cardiac activity.
“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 of ETH Zurich.
Pink noise, which sounds like static, causes the heart “to contract and relax more vigorously”, in particular the left ventricle, whose role is to distribute oxygen-rich blood to the body’s organs, muscles and tissues.
The more vigorous the contraction and relaxation, the greater the blood flow, hence the positive impact on the cardiovascular system.
“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 surprised us,” said project leader and sleep expert Caroline Lustenberger.
“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,” she added.
The researchers need to take these findings further, especially to include women in their future research to take into account gender differences in sleep and cardiovascular health. Women were not included in the original study because of the influence of the menstrual cycle or menopause on sleep, which could have skewed the results over such a short study period.
Still, the experts are excited by these initial discoveries and see many potential long-term benefits, “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,” Huwiler noted.