Ultrasonic sensors for monitoring the condition of a vascular graft

DETAILED DESCRIPTION The invention in which an exclusive right is claimed is defined by the following: 1.
A graft adapted to be coupled into a patient's vascular system, comprising: (a) a biocompatible material formed into a generally cylindrical shape and having a circular wall defining a lumen extending along a longitudinal axis of the graft, said lumen being adapted to convey a fluid through the graft; (b) a first transducer disposed within the wall of the graft, said first transducer producing a signal indicative of a parameter of the fluid flowing through the lumen; and (c) a coil coupled to the first transducer for conveying the signal to a point external to the patient's body, for use in evaluating a condition of the graft.
2.
The graft of claim 1, wherein the first transducer comprises a first pressure sensor and the signal is indicative of a pressure of the fluid in the lumen.
3.
The graft of claim 2, further comprising a second pressure sensor disposed within the wall of the graft, said second pressure sensor also producing a signal indicative of the pressure of the fluid in the lumen, said first pressure sensor being disposed adjacent one end of the graft and said second pressure sensor being disposed adjacent an opposite end of the graft, to monitor the pressure of the fluid in the lumen at each end of the graft, a difference between the pressure of the fluid at each end of the graft providing an indication of the condition of the graft.
4.
The graft of claim 1, wherein said first transducer includes a plurality of elements formed on a piezoelectric substrate, which when excited by a radio frequency signal, emit ultrasonic waves that propagate into the lumen, said ultrasonic waves being affected by the fluid flowing through the lumen, further comprising a receiver of the ultrasonic waves that produces the signal indicative of the parameter, said receiver being coupled to the coil so that the signal produced by the receiver is conveyed outside the patient's body.
5.
The graft of claim 4, wherein the parameter is one of a velocity and a flow of the fluid through the lumen of the graft, said signal indicative of the parameter being determined as a function of the fluid's effect on the ultrasonic waves within the lumen