Exposure to remifentanil contributes to an increased risk of pulmonary aspiration, likely through reduced pharyngeal contractile vigour and diminished bolus propulsion during swallowing. Here, we employed a novel high resolution pressure-flow analysis to quantify the biomechanical changes across the upper esophageal sphincter (UES). Eleven healthy young participants (mean age 23.3±3.1 years, 7 male) received remifentanil via intravenous target controlled infusion with an effect-site concentration of 3 ng/ml. Before and 30 min following commencement of remifentanil administration, participants performed ten 10 ml saline swallows while pharyngo-esophageal manometry and electrical impedance data were recorded using a 4.2 mm diameter catheter housing 36 circumferential pressure sensors. Remifentanil significantly shortened the time period of UES opening (p<0.001) and increased residual UES pressure (p=0.003). At the level of the hypopharynx, remifentanil significantly shortened the time latency from maximum bolus distension to peak contraction (p=0.004) and significantly increased intrabolus distension pressure (p=0.024). Novel mechanical states analysis revealed that the latencies between the different phases of the stereotypical UES relaxation sequence were shortened by remifentanil. Reduced duration of bolus flow during shortened UES opening in concert with increased hypopharyngeal distension pressures are mechanically consistent with increased flow resistance due to a more rapid bolus flow rate. These biomechanical changes are congruent with modification of the physiologic neuro-regulatory mechanism governing accommodation to bolus volume.