To investigate the effect of body position in sliding hiatal hernia (SHH).

This study was a retrospective controlled study. A total of 153 patients with suspected gastroesophageal reflux disease who attended the Department of Gastroesophageal Surgery at the PLA Rocket Force Characteristic Medical Center between March 2, 2022, and March 6, 2023, were enrolled. All patients underwent upper gastrointestinal endoscopy and high-resolution esophageal manometry (HREM) in both the seated and supine positions. The upward displacement length of the esophagogastric junction (EGJ) was measured by endoscopy. Data including esophageal length, lower esophageal sphincter (LES) length and pressure, and the crural diaphragm-LES (CD-LES) separation distance were collected. Based on an EGJ upward displacement greater than 2 cm on endoscopy and the presence of CD-LES separation on HREM, patients were divided into the SHH group (62 cases) and the non-SHH group (91 cases). Differences in the above parameters between seated and supine positions within each group, as well as differences between the two groups, were analyzed.

Among the 153 patients, SHH was detected in 62 cases (62/153, 40.52%). The detection rate of SHH by supine HREM (30.01%) was significantly higher than that by endoscopy (24.18%) and seated HREM (12.41%), with statistically significant differences (P<0.05). In the SHH group, esophageal length and intra-abdominal LES length measured in the supine position were shorter than those measured in the seated position, while the CD-LES separation distance was longer in the supine position. The minimum and mean LES resting pressures and LES residual pressure were all higher in the supine position than in the seated position, with statistically significant differences (P<0.05). In the non-SHH group, esophageal length measured in the supine position was shorter than that in the seated position, whereas the minimum and mean LES resting pressures and LES residual pressure were higher in the supine position, with statistically significant differences (P<0.05). Regardless of body position, the CD-LES separation distance in the SHH group was longer than that in the non-SHH group, while esophageal length, LES length, and intra-abdominal LES length were shorter in the SHH group. In addition, the minimum and mean LES resting pressures and LES residual pressure were lower in the SHH group than in the non-SHH group, with statistically significant differences (P<0.05).

Body position can influence sliding in hiatal hernia. Compared with the seated position, the supine position causes the EGJ to shift further toward the thoracic cavity, increases the extent of herniation into the thorax, and enlarges the volume of the hernia sac.