Effect of Plunger Design on the Constricting Forces in an Adjustable Systemic to Pulmonary Artery Shunt

Abstract

Hypoplastic left heart syndrome (HLHS) is a leading cause of cardiac death among newborns, in which the entire left side of the heart is underdeveloped and unable to support the blood circulation. It is the most common type of single ventricle physiology (SVP) and an important need for an adjustable systemic to pulmonary artery (SPA) shunt. In order to achieve full range control of blood flow between the systemic and pulmonary circulation, an adjustable SPA shunt is being developed. SPA shunts are generally made from FDA approved polytetrafluroethylene (PTFE). A screw-plunger mechanism is being used to cause the desired constriction in the pressurized shunt. It is necessary to optimize the design of the plunger, in order to vary the cross-section of the shunt with minimum forces required. An in vitro set up consisting of a hydraulic circuit to have a constant inlet pressure to the shunt throughout the process and a certain post shunt pressure initially, plunger attached to the force gauge mounted on a stand to cause constriction and measure forces, a mounting stand to hold the shunt and its casing, a flow meter and pressure transducers, is used to determine the effect of various plunger tip shapes. It was observed that wider the plunger, lesser is the force required to cause the same reduction in flow. Flow-displacement-force variations for each plunger tip used are also presented. Results from this study will be used to determine the torque required to drive the screw plunger mechanism to cause the desired constriction.