The current science of gastric banding: an overview of pressure-volume theory in band adjustments.

BACKGROUND: Laparoscopic adjustable gastric banding (LAGB) is a safe and effective bariatric operation for the treatment of morbid obesity. Optimized long-term weight loss and reduced complications may be facilitated by development of a standardized, accurate, band-fill measurement methodology for use in postoperative LAGB adjustments.
METHODS: A summary of the primary in vitro, theoretical, and in vivo studies of pressure-volume theory relative to gastric banding was undertaken.
RESULTS: LAGBs range in mechanisms of action from low-pressure/high-volume to high-pressure/low-volume. Use of both basic and dynamic pressure data obtained experimentally and clinically with a low-pressure/high-volume (LP/HV) band as a research tool revealed that intra-band pressures remained very low even when the band balloon was filled to its maximum fill volume; in contrast, when a high-pressure/low-volume (HP/LV) band was filled, it exhibited a pressure curve markedly steeper and of greater amplitude than that of the LP/HV band. Theoretical calculations of the differences between the bands in terms of the pressures they exerted on a bolus of food passing through a stoma found that the pressure created by the HP/LV band against the gastric wall was >100% higher than that applied by the LP/HV band; these mathematical results were verified by using invasive manometry in 35 patients undergoing band adjustment. In clinical testing, basic band pressure, band volume, and dynamic pressure data (that demonstrated esophageal motility patterns at the stoma during bolus passage) were gathered and correlated. As identified by intra-band pressure readings, a zone of disruptive peristaltic activity that obstructed bolus passage through the stoma was observed; slightly beneath this zone, it was hypothesized that successful patient adjustments might be carried out. The manometrically delineated measure of mean band pressure sufficient to exert a significant yet not disruptive restriction (i.e., 20 mm Hg; mean volume of 5.4 mL) was tested in 25 patients in follow-up. No patient required readjustment due to obstruction. Intra-band pressure, as opposed to band-fill-volume measurement, per se, was shown to produce a more accurate measurement of actual band (stoma) restriction in individual patients, and to identify a pressure "green zone" for effective restriction at adjustments. DISCUSSION: Ongoing scientific studies are needed to refine pressure-volume theory by using laboratory, theoretical, and clinical manometry to establish a reliable pressure-based algorithm for gastric band adjustment. Such an algorithm may lead to more consistent weight loss, fewer complications, and more compliant patients.