Bench radial force testing of the wire sphere

Retriever Medical's thrombectomy device for DVT and PE uses two wire spheres that the user expands, collapses and moves by hand. An earlier pig study found no vessel wall damage, even with the spheres expanded to 200% of vein diameter.

This study measured the radial force, the outward push on the vessel wall, when a sphere Is expanded. Knowing it helps judge the risk or rupturing a vessel during use.

• Tester: the collapsed sphere was placed in an MSI RX650 Radial Force Tester, which has an adjustable iris that acts like a vessel.
• Three sizes: the iris was set to 5 mm, 7.5 mm and 10 mm. At each size the sphere was expanded until the force leveled off.
• Straight path: the device was first delivered along a straight course.
• Winding path: It was then delivered through a 180 degree bend (4 cm radius) and a 90 degree bend (8 cm radius).

The expanded sphere produced at most 22 N of radial force. Force went up as the iris diameter went from 5 mm to 10 mm. The straight and winding paths gave no significant difference in force.

Published burst pressures for the saphenous vein and pulmonary artery are far above the sphere's force, so vessel rupture during use is highly unlikely. With the earlier pig study, this adds support for the device's safety profile.