We already know there's a link between insomnia symptoms and heart health. A study published in March 2016 now suggests that one insomnia symptom in particular is associated with longer heart rate recovery times.
Since insomnia symptoms are common in those with heart disease, Canadian researchers set out to determine whether insomnia symptoms are linked to lower parasympathetic tone in heart rehabilitation patients with suspected insomnia.
What is parasympathetic tone?
The parasympathetic nervous system is one of two main divisions of the autonomic nervous system, which is responsible for regulating our internal organs.
Under normal conditions, parasympathetic neurons “fire” at a constant rate, maintaining heart rate and keeping blood pressure within a normal range. This “firing” is known as the parasympathetic tone.
If parasympathetic tone is reduced, sympathetic activity increases, which can lead to hyperarousal (a response not dissimilar to the fight or flight response we experience when in a stressful situation).
When we exercise, our heart rate rises as sympathetic activity increases and parasympathetic activity decreases.
When we finish exercising, sympathetic activity decreases and parasympathetic activity increases, allowing our heart rate to recover.
It can be difficult to measure parasympathetic tone — however, a number of non-invasive methods are used, including:
Resting heart rate
Peak exercise heart rate
Heart rate variability
Heart rate recovery
Researchers set out to see if there was an association between individual insomnia symptoms and parasympathetic tone, as measured by heart rate recovery one minute after the cessation of exercise.
The study involved 121 individuals on a 12-week cardiac rehabilitation program.
Sleep was measured using the Insomnia Severity Index, which assesses sleep based on seven measures, including difficulty falling asleep and difficulty staying asleep.
Heart rate recovery was measured using an ECG to record heart rate from rest until five minutes after the end of a maximal exercise test.
Researchers found that individuals who found it harder to fall asleep were more likely to have slower heart rate recovery times. This association was even stronger in those with moderate to severe insomnia symptoms.
This finding suggests that difficulty falling asleep may be linked with reduced parasympathetic tone (and the hyperarousal this can cause).
This has a negative effect on sleep as sleep relies on a healthy autonomous nervous system that is able to reduce arousal by increasing parasympathetic tone.
Unfortunately, we still don't know for sure whether reduced parasympathetic tone is a consequence of difficulty falling asleep, or if difficulty falling asleep is a consequence of reduced parasympathetic tone.
How to reduce hyperarousal and fall asleep faster
If you find it difficult to fall asleep, one of the best things you can do is relax and avoid trying to actively fall asleep.
Sleep is a natural process that doesn't need our intervention. As soon as we intervene and try to force sleep, sleep becomes more difficult.
Instead, get into bed at night and relax. Tell yourself that you're simply going to lie down and see what happens.
If you don't fall asleep after half an hour or so, get out of bed and do something unstimulating, such as reading a book. After half an hour, get back into bed for another relaxation session.
Keep repeating this process until you are able to fall asleep.
Another technique that can help is guided relaxation. It can distract the mind from negative thoughts and worries about sleep.
As soon as you recognize that you are in control of your thoughts, the sooner you can use that knowledge to remove the fear and anxiety from sleep, reduce hyperarousal, and fall asleep faster.
Martin is the creator of Insomnia Land’s free sleep training for insomnia. His online course uses CBT for insomnia techniques to help participants fall asleep and stay asleep. More than 4,000 insomniacs have completed his course and 97 percent of graduates say they would recommend it to a friend.