Pronounced alterations in heart rate variability may contribute to sudden unexpected death in epilepsy (SUDEP), scientists including one of Indian-origin say.
Doctors have long characterised epilepsy as a brain disorder, but researchers from Case Western Reserve University in the US have now found that part of the autonomic nervous system functions differently in epilepsy during the absence of seizures.
This connection to the involuntary division of the nervous system may have implications for diagnosing and treating the disease and understanding SUDEP, researchers said.
They studied the electrocardiograms of 91 children and adolescents with generalised epilepsy, and 25 neurologically normal children during 30 minutes of stage 2, or light, sleep. No subjects were suffering from a seizure during these intervals.
They found that respiratory sinus arrhythmia - the increase in heart rate during inhalation and decrease during exhalation - was more pronounced in patients with epilepsy, and that their heart rate also was significantly lower.
Those changes are consistent with increased firing of the vagus nerve in children with epilepsy, compared to those without, researchers including Siddharth Sivakumar suggest.
The vagus nerve is the main trunk of the parasympathetic nervous system. The more the vagus fires, the more it slows the heart, especially during exhalation, researchers said.
They found no difference in blood pressure between the two groups of children, indicating the sympathetic nervous system, which is responsible for fight-or-flight responses, is not involved.
All of the children in the study had electroencephalograms monitoring their brain activity during the 30-minute periods of sleep. There was no abnormal activity found there, either.
“All the findings of our study on heart rate variability in epilepsy point to increased activity in the parasympathetic nervous system during sleep,” said Roberto Fernandez Galan from Case Western Reserve University.
Specifically, the parasympathetic - or “rest-and-digest” nervous system modulates breathing and slows the heart rate of sleeping children with epilepsy substantially more than in healthy children, researchers said.
They also found that several children who had been diagnosed as neurologically normal - but had similar strong modulation and low heart rates - were later diagnosed with epilepsy.
The discovery suggests that changes in the parasympathetic tone precede the onset of epilepsy in children, researchers said. The findings were published in the Journal of Neurophysiology.