Fig. 2. Repetitive vagal nerve stimulation (VNS) or intravenous acetylcholine (ACh) yields stable effects over time on pulmonary inflation pressures or bradycardia in the absence of muscle relaxants. Alternating stimuli were given every 5 min (see fig. 1 ) for a total of eight cycles. Responses are expressed as a percentage of the pulmonary inflation pressure increase induced by the first ACh and VNS challenge or the degree of bradycardia induced by the first VNS. The magnitude of the pulmonary inflation pressure or bradycardic responses did not differ from the initial response ( P > 0.05; n = 8).