Sleeve device functions as a starling resistor to record sphincter pressure

In 1976 Dent (Gastroenterology 71:263-267) introduced a sleeve-catheter device for obtaining continuous recording of lower esophageal sphincter pressure. The infused sleeve accomodates for axial sphincter movement by providing a large surface of collapsible membrane that is capable of sensing maximal sphincter pressure at any point along the sleeve. Although sleeve performance was tested previously, the precise physical principal of its function has not been delineated. This study tests the hypothesis that the sleeve device functions as a Starling resistor. The term 'Starling resistor' is an eponym that designates the physics of fluid flow through collapsible tubes. When pressure at any point along an infused collapsible conduit is greater than the intraluminal pressure at the distal end of the conduit, partial collapse occurs at some axial location along the conduit where the transmural pressure equals zero. The location of zero transmural pressure is termed the 'equal pressure point' (EPP). The partial collapse at the EPP causes a local change in luminal resistance that is directly related to the magnitude of the external pressure at the EPP and accompanied by a corresponding change in the pressure upstream from the EPP. A correlate to the performance of Startling resistors is that the pressure upstream to the EPP is not affected by the downstream pressure, so long as the downstream pressure is less than the external pressure. To test our hypothesis, we evaluated sleeve performance in vitro using a two-chambered model that allowed application of static or oscillatory pressures at one or two sites along the sleeve. Fluid flow through the sleeve was varied from 0.1 to 1.0 ml/min using a noncompliant infusion system. The results showed that the upstream pressure of the infused sleeve invariably recorded the highest static or oscillatory pressure acting at any point along the sleeve. Second, recorded pressures were independent of the sleeve device functions as a Starling resistor to provide accurate recordings of sphincter pressure.