Infrared diameter gauge for in vitro mechanical testing of vascular grafts

A diameter gauge employing modulated infrared radiation has been developed for in vitro mechanical testing of small diameter vascular grafts. A linear range of greater than 6 mm has been achieved using a 100 mm2 photodiode. The device is immune to ambient illumination. Temperature stability has been greatly improved by using a simple closed-loop control circuit. The pressure-diameter relationship of a polyurethane artery graft, 4 mm internal diameter, has been determined under static and dynamic loading. The results show that the distensibility of the graft is relatively constant up to about 6 Hz but increases rapidly at frequencies greater than 10 Hz.