VNS & Apnea
A small study, published in the November 2000 issue of the journal
Neurology, shows that vagus nerve stimulation (VNS) devices may affect the breathing of some users during sleep.
Funded by the US National Institute of Neurological Disorders and Stroke and by Cyberonics, Inc., the manufacturer of the VNS device, the study was led by Beth Malow, MD, MS, assistant professor of neurology at the University of Michigan. The study looked at 4 U of M epilepsy patients with the VNS implant, to assess the effects of VNS on daytime sleepiness. All participated in overnight sleep tests at U of M's Michael S. Aldrich Sleep Disorders Laboratory, both before and after the devices were implanted. The study shows a positive effect from low to medium VNS intensities.
However, nighttime breathing problems were noticed during monitoring of their overnight airflow, blood oxygen and effort. All had more breathing decreases or interruptions when the device was cycling than when it was off. Most of the breathing events were not severe or long-lasting enough to be classed as apneas or hypopneas.
One male with pre-existing undiagnosed obstructive sleep apnea experienced an increase from 4 apneas or hypopneas per total hour of sleep before the implant to 11 per total hour of sleep after receiving the device (including both cycling and off time). The others, who showed no signs of apnea in their baseline tests, also experienced an increase in apneas and hypopneas, although these remained within the normal range: fewer than 5 per hour. Calculations show the rate of interruption while the device was actually stimulating the vagus nerve to be 19 per hour. Follow-up studies of 2 patients show that fine-tuning of their VNS devices may help to reduce breathing disruptions. The person with pre-existing apnea and 1 of the others showed a decrease in apneas and hypopneas when the VNS stimulus frequency was decreased.
The unexpected effect, which appears small and not harmful, may help doctors identify and treat persons susceptible to sleep apnea before they begin using the VNS device and could aid in understanding how the device works.
Further studies of larger groups of people are called for, to help understand vagus nerve stimulation, what conditions it may exacerbate and to learn how to address any confirmed side effects.
These new finding add to the growing understanding of sleep and epilepsy. Recently published results of a study by Dr. Malow and her colleagues show that approximately 33% of persons with epilepsy which is not controlled successfully by medication may have sleep apnea. (In the general population, about 24% of men and 9% of women experience apnea.) This frequent coexistence of both conditions may indicate an interaction between the areas of the brain involved in seizure activity and those which control breathing.
Sleep apnea is often undiagnosed. If untreated, the disorder can affect daytime performance, blood pressure, and heart and lung function. Sleep apnea may exacerbate seizures or daytime sleepiness for persons with epilepsy.
More Information Apnea = 80% percent or greater decrease in breathing for more than 10 seconds
Hypopnea = breathing interruption for more than 10 seconds with partial awakening or decrease in blood oxygen
