Fig. 1.

Methods to assess whether vagal nerve stimulation (VNS) is sufficient for respiratory rhythm variability and Hering-Breuer input-output entrainment in situ. A: we measured left phrenic (PNA) and right vagal nerve (VNA) activities, while rhythmically forcing the network at its intrinsic oscillation frequency (ω0) via left VNS. B1: threshold amplitude for the electrical stimulus to evoke the Hering-Breuer reflex (HBR) was defined not only by the suppression of inspiratory activity on PNA (bottom), but also by the presence of evoked bursts of efferent VNA from the contralateral vagus nerve (top). B2: stimulus-triggered average of integrated efferent right VNA during a rhythmic VNS trial is shown. The rhythmic VNS (red trace) consistently evoked bursts of efferent VNA (green traces: thick line is the averaged activity; and thin lines, plus and minus standard deviation) at a delay of ~250 ms.