Abstracts

RATIONALE: Vagus nerve stimulation (VNS) has been associated with hoarseness, dyspnea, and laryngeal irritation. We report sleep-related decreases in airflow and effort coinciding with VNS, and improvement in these respiratory events with reduction in stimulus frequency. METHODS: Four epilepsy patients underwent polysomnography (PSG) before treatment and after 3 months of treatment with VNS. Respiratory airflow, effort, oxygen saturation, EEG, chin EMG, EOG, and VNS stimulation signal were recorded. VNS effects on respiration were quantified. Stimulus parameters were 1-2 mA stimulus intensity, 500 ?sec pulse width, 30 secs on time and 5 min off time, and 30 Hz. RESULTS: Sleep-related decreases in airflow and effort coinciding with VNS activation were observed consistently in all patients. Most events did not meet criteria for scorable apneas (10 second airflow or effort ? 20% of baseline) or hypopneas (10 second airflow or effort reduction associated with EEG arousal or ? 4% oxygen desaturation). Treatment apnea-hypopnea index (AHI) for three patients was within normal limits (<5 apneas and hypopneas per hour). In one patient with witnessed apneas before VNS treatment, AHI rose from 4 (pretreatment) to 11.3 (treatment; stimulus intensity of 1 mA). In this patient, scorable events, mostly hypopneas, were more likely to occur with VNS stimulation (p<0.0001; chi-square test). During a third PSG (stimulus intensity of 1.5 mA, other parameters unchanged), apneic events occurred coinciding with VNS even when pulse width was reduced to 130 ?sec or on time was reduced to 7 secs. Reducing stimulus frequency to 10 or 20 Hz markedly reduced VNS-related apneas and hypopneas. CONCLUSIONS: Sleep-related decreases in airflow and effort coincided with VNS. In patients without preexisting sleep apnea (SA), this VNS effect is probably not clinically significant. In one patient with preexisting SA, increasing stimulus intensity contributed to scorable respiratory events, yet decreasing stimulus frequency ameliorated them. Care is advised in treating patients with preexisting SA with VNS. Lowering stimulus intensity or frequency may prevent exacerbation of SA. Study supported by Cyberonics and NINDS KO2 NS02099