Mechanism of association between BMI and dysfunction of the gastro-oesophageal barrier in patients with normal endoscopy

Mohammad H Derakhshan, Elaine V Robertson, Jonathan Fletcher, Gareth-Rhys Jones, Yeong Yeh Lee, Angela A Wirz, Kenneth EL McColl

Introduction
The association between BMI and GORD is incompletely understood. We examined the association between BMI and gastro-oesophageal (GO) barrier function and the effect of mechanically increasing intra-abdominal pressure on GO physiology.

Methods
(A) 103 dyspeptic patients with normal endoscopy underwent 24-hr pHmetry and upper gastrointestinal manometry. Relationship between BMI and acid reflux, intragastric pressure (IGP), gastro-oesophageal pressure gradient (GOPG) and lower oesophageal sphincter (LOS) pressure were calculated using bivariate correlations.
(B) In 18 healthy volunteers, the effects of increasing IGP by abdominal belt on GO manometry were studied.

Results
(A) There was a linear correlation between BMI and oesophageal acid exposure in erect (R=
0.35, p<0.001) and supine (R= 0.40, p<0.001) positions. BMI was strongly associated with IGP (inspiration R= 0.66, p<0.001, expiration R= 0.78, p<0.001) and inspiratory GOPG (R= 0.50, p<0.001). There was a positive correlation between BMI and inspiratory LOS pressure relative to atmospheric pressure (R= 0.29, p=0.016) and a negative correlation with LOS pressure relative to IGP on expiration (R= -0.25, p=0.018). Logistic regression models using all significant manometric variables and relevant interactions revealed marked decline in the magnitude and significance of relationship between BMI and oesophageal acid exposure in both supine [from OR: 1.12 (95% CI: 1.03-1.22), p=0.009 to 1.00 ( 0.86-1.17), p=0.999] and upright positions [from 1.11 (1.02-1.20), p=0.020 to 1.03 (0.89-1.18), p=0.717].
(B) Application of the constricting abdominal belt produced similar manometric changes to those associated with increased BMI. However, the belt did not reproduce the reduced LOS pressure relative to IGP.

Conclusion
The association between reflux and BMI may be largely explained by effects of increased intra-abdominal pressure. However, the reduced LOS pressure associated with BMI may be mediated by another mechanism or effects of chronic rather than acute elevation of intra-abdominal pressure.

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