Increased pumping performance after nights in the sleep laboratory: Using a deep sleep stimulation technique, researchers have shown how the cardiovascular system benefits from healthy sleep. The intensification of sleep through short tones led to the heart contracting more strongly and being able to relax again. In addition to providing insight into the physiological significance of deep sleep, the stimulation technology also has potential for medical applications, say the scientists.
Unfocused and weak: Too little or poor sleep is known to lead to unpleasant mental and physical symptoms. The impact of sleep on human health has been intensively researched for a long time. Deep sleep has proven to be a particularly important part of restful sleep. It is characterized by a slow wave of brain activity and promotes the regeneration processes in the body. Impairment of deep sleep can, among other things, affect the cardiovascular system. However, it is not yet known exactly what function this connection is based on.
Acoustic stimulation
The research team led by senior author Caroline Lustenberger from the Swiss Federal Institute of Technology in Zurich (ETH Zurich) has now investigated the previous assumption that a healthy deep sleep improves the heart's pumping performance. To do this, they used a technique that has been successfully developed at ETH Zurich for several years: it has been shown that deep sleep can be intensified using special acoustic stimuli. Short, gentle tones are placed on the test subjects' ears as soon as a system detecting their brain waves indicates that they have fallen into deep sleep. A computer system then adapts the acoustic stimuli to the course of brain activity. This can then increase the intensity of deep sleep.
18 healthy men between the ages of 30 and 57 took part in the study to investigate the possible effect of this technique on heart function. They spent three non-consecutive nights in the sleep laboratory. In two of the test runs, the researchers stimulated the test subjects with the deep sleep-enhancing system, but not in one night. They continuously recorded the subjects' brain activity, blood pressure and heart activity while they slept. These measurements were then processed and analyzed by a computer system. In addition, the subjects' cardiac function was examined after the nights in the sleep laboratory using echocardiography.
As the scientists report, they found surprisingly strong effects of the treatment. Initially, there was a direct influence on cardiac activity: “During the stimulation, we clearly saw an increase in deep sleep waves, which was accompanied by a response from the cardiovascular system that was reminiscent of a cardiovascular pulsation,” says first author Stephanie Huwiler from ETH Zurich . The findings on the following day were particularly striking: “We clearly saw that both the pumping power and the relaxation ability of the heart are greater after nights with stimulation compared to nights without,” says co-author Christian Schmied from the University of Zurich. Lustenberger says: “We were surprised that sound stimulation during deep sleep had such a significant effect on the cardiovascular system after just one night.”
Left ventricle strengthened
Specifically, the study results showed that the promotion of brain waves during deep sleep causes the left ventricle in particular to contract more strongly and relax again. This means more blood enters the circulation and less remains in the heart. This in turn increases blood flow, which has a positive effect on the cardiovascular system. “Despite the relatively small group of test subjects, the results are significant. We also reproduced the results on two independent nights, which is statistically very strong,” says Lustenberger.
As the team explains, the study has now clarified how deep sleep is linked to a healthy cardiovascular system. The scientists also see therapeutic potential in their procedure. “The treatment of cardiovascular diseases could be improved with this or similar stimulation procedures,” says Lustenberger. Huwiler adds: “Particularly in prevention, but also in competitive sports, such a deep sleep stimulation system could enable improved cardiac functions in the future – and possibly ensure faster and better regeneration,” says Huwiler.
The researchers are now planning to explore the extent to which special stimulation methods can improve the cardiovascular system even more intensively. In addition, the study with the relatively small group of men is to be followed by more extensive tests: “It is now important to investigate to what extent women can also benefit from such a deep sleep stimulation method,” says Lustenberger.
Source: Swiss Federal Institute of Technology Zurich (ETH Zurich), specialist article: European Heart Journal, doi: 10.1093/eurheartj/ehad630