Comparison of effects of upright versus supine body position and liquid versus solid bolus on esophageal pressures in normal humans.

New studies monitoring ambulatory esophageal pressures during food ingestion often compare results to normal values obtained from supine liquid swallows. We compared distal esophageal peristaltic and lower esophageal sphincter (LES) pressures in 15 normal subjects during six liquid swallows in the upright and supine positions, and six solid (small marshmallow) swallows in upright position. LES pressures were significantly (P less than 0.05) higher supine than upright but no differences were noted in LES pressure, relaxation, and duration of relaxation between upright solid and liquid swallows. Distal peristaltic wave velocities were faster upright than supine. Peristaltic wave amplitudes, durations, and DP/DT were significantly (P less than 0.05) greater in supine than in upright position. Atypical wave forms, defined as nontransmitted, simultaneous, and simultaneous/repetitive, increased in the upright position compared to supine (P less than 0.01), and during solid vs liquid swallows (P less than 0.05). These results indicate that body position substantially affects normal distal esophageal peristalsis and LES pressure and that "abnormal" wave forms occur more frequently during swallowing solids than liquids in the upright position. Conclusions regarding "abnormal" motility over prolonged periods and during food ingestion in patients should be tempered by these findings.