Abstracts

RATIONALE: Vagal afferents influence the principle brainstem nuclei involved in regulation of respiration. Animal studies have found minimal changes in respiration with vagal nerve stimulation. In humans, stimulation of the vagus nerve has not demonstrated any acute effects on spirometry, yet changes in respiration may be sleep stage dependent. METHODS: To evaluate the effect of vagal nerve stimulation on sleep dependent respiratory function, we performed polysomnography on seven patients prior to and following three months of high intensity, high frequency vagal nerve stimulation. Respiratory rates, oxygen saturation, end-tidal CO2, upper airway resistance (as measured by intranasal pressure) and respiratory disturbance index were measured in each stage of sleep. During the stimulation study, measures were taken from both parts of the duty cycle (stimulator on and off). Findings were compared using an ANOVA analysis (p<0.05) RESULTS: We found that 6 of 7 subjects had increase in respiratory rate during REM sleep, whereas other stages of sleep did not have consistent changes in respiratory rate. End tidal CO2 did not significantly differ in wake, stage 2 or REM sleep, but 6 of 7 subjects had lower end-tidal CO2 (change >5 torr) in stage 3 & 4 sleep. Oxygen saturation, measured by peripheral transcutaneous sensors, did not change in regards to stimulation. Events of increased upper airway resistance increased on average from 6.8 events per hour to 10.0 events per hour during periods of stimulation. These events were not associated with significant oxygen desaturations or increases in end-tidal CO2, and patients did not complain of daytime symptoms referable to obstructive sleep apnea. CONCLUSIONS: This study shows that chronic vagal nerve stimulation may alter sleep dependent respiration. The increase in respiratory rate in REM sleep and decrease in end-tidal CO2 in slow wave sleep suggests that this interaction is complex. During vagal nerve stimulation airway resistance may increase in some patients, but the effect of this increase resistance has yet to be determined. Further study is indicated to delineate the exact alteration vagal nerve stimulation has on respiratory function.