Vagal nerve stimulation induces intermittent hypocapnia

PURPOSE: To study whether respiratory alteration caused by vagal nerve stimulation (VNS) can change end-tidal carbon dioxide (EtCO2) levels. METHODS: We performed polygraphic recordings including capnographic monitoring during daytime sleep on adults with VNS therapy. RESULTS: Ten of 13 patients showed VNS-induced alterations in the frequency or amplitude of respiration. Five patients had a consistent increase in respiratory rate with a simultaneous, consistent and significant decrease (p < 0.01; 5-22%) in EtCO2 during VNS. Three subjects showed occasional decreases in EtCO2 during VNS, and two showed no clearly detectable VNS-related EtCO2 changes. CONCLUSIONS: Our findings suggest that VNS may alter brain CO2 levels through changes in respiration. Because carbon dioxide (CO2) has potent effects on various brain functions, it is possible that these transient CO2 changes may have an effect on the state transitions between interictal and preictal states.