Children with insomnia and shorter sleep duration had impaired modulation of heart rhythm during sleep, Pennsylvania researchers reported at the American Heart Association’s 50th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.

In a study of young children, researchers showed that insomnia symptoms were consistently associated with impaired heart variability measures. They also found a significant but less consistent pattern with shortened sleep duration and decreased heart rate variability.

Heart rate variability is the beat-to-beat variations of heart rate. In a healthy person, beat-to-beat intervals change slightly in response to automatic functions like breathing.

The study included 612 elementary school children in the first to fifth grades. The children were average age 9, 25% were non-white, and 49% were boys. All were generally in good health. Their parents completed the Pediatric Behavior Scale, including two questions that focused on symptoms of insomnia.

Researchers examined the children overnight in a sleep laboratory with polysomnography. The researchers measured sleep duration, trouble falling asleep, the number of wake-ups, and problems going back to sleep if awakened. They also measured cardiac autonomic modulation (CAM), the balance of the sympathetic and the parasympathetic control of the heart rate rhythm.

A balance is needed between the sympathetic modulation that "excites" the heart and the parasympathetic modulation that "calms" the heart, said Fan He, lead author of the study and a graduate student at Penn State University College of Medicine in Hershey, Pa. "The balance between the sympathetic and the parasympathetic provides a favorable profile for the heart."

The study showed:
• Children with reported insomnia had impaired CAM with a shift toward more sympathetic or excitable activation of the heart rhythm. There was a 3% to 5% reduction in the parasympathetic modulation of heart rhythm in children with insomnia.
• Children with longer sleep duration had a slower heart rate indicative of a balance of heart rhythm, with a shift toward more parasympathetic modulation. The heart rate of children who slept 8 hours was two beats per minute slower than that of kids who slept only 7 hours.
• Insomnia and short sleep duration, even in young children, resulted in a physiological activation of the sympathetic modulation.

"Kids who sleep a longer duration have a healthier heart regulation profile compared to kids who sleep shorter durations," said Duanping Liao, MD, PhD, coauthor of the study and professor of epidemiology at Penn State University College of Medicine. "Their hearts are more excitable if they have insomnia. If the heart is too excited, that means it is beating too fast and usually that isn’t good. These data indicate that among young children with insomnia symptoms reported by their parents, there already is an impairment of cardiovascular autonomic regulation, long before they reach the traditional high-risk period for cardiovascular disease."