Summary We examined the value of impedance monitoring in measuring bolus volume
compared with videoesophagram. Eighty consecutive subjects were studied with
simultaneous impedance-manometry-videoesophagram. A catheter with both an impedance
electrode pair and a pressure transducer at four sites (5, 10, 15, 20 cm above lower
esophageal sphincter) was passed per nares. Six 10-cc boluses of 45% barium mixed with
0.9% NaCl were swallowed at 20-to 30-second intervals. When impedance fell to below