Fig. 1. Study design illustrating initial alternating challenges with vagal nerve stimulation (VNS) ( solid arrows ) and intravenous acetylcholine (ACh) administration ( dashed arrows ) and the effects on blood pressure (BP), pulmonary inflation pressure (Ppi), and heart rate (HR). VNS and intravenous ACh independently induce transient increases in Ppi (*) and bradycardia (#) with resultant decrease in BP (#). After consistent responses, incrementally increasing doses of muscle relaxants are administered intravenously with repeat challenges with VNS and intravenous ACh.