Fig. 2
Awake verification of target engagement and electrode reliability/stability. A Representative measurements of heart rate, respiration rate and partial pressure of carbon dioxide (PCO2) during consecutive periods of VNS (10 s on, 30 s off) for NHP Dk 39 days post implant. Gray bars denote the period VNS is turned on. Similar to the anesthetized, intraoperative testing, we see noted parasympathetic effects on the rate of respiration. This depressive effect on respiration is plainly visible in the raw PCO2 time series (black) and its envelope (red trace). B Average change in respiration rate (black trace) and PCO2 (blue trace) for NHPs Dk, An and Mi measured 39, 86 and 122 days post implant, respectively. Stimulation amplitudes were 1000µA, 500µA and 1000µA for Dk, An and Mi, respectively. Again, we find robust parasympathetic effects on respiration but not heart rate, with the most profound effect being seen in PCO2. Arrows represent the average time VNS was applied to evoke these average responses. C Dose response curves demonstrating changes in PCO2 as a function of stimulation current amplitude. Greater levels of stimulation resulted in larger decreases in PCO2 during stimulation. D Impedances of the VNS electrode, measured at 1 kHz, remain stable throughout the duration of the experiment