the diameter of the probe need not be constant across the transducer fig6 c depicts a cross sectional view of the probe of fig6 a but in which the diameter of the probe varies the widths distal d and proximal d u2032 to the transducer 164 are less that the width necessary to encompass the transducer 164 this configuration functions because the wider diameter at the transducer 164 and opening 160 is not located within the stenotic region when pressure is measured hence the diameter of the vessel in the region outside the stenosis is sufficiently large to permit pressure to enter through hole 160 without constricting flow and generating an anomalous pressure reading fig7 a b show cross sectional views of an alternative construction of an optical pressure probe similar to the probe shown in fig6 the distal end of the probe shown here is constructed from a long flexible hollow tube 150 or an assembly of tapered tubes with the pressure sensing port located at the base of its spring tip 154 however the probe shown in fig7 b includes a disposable optical adapter 172 that gives the operator access to the proximal end of the adapter this configuration enables the pressure probe to serve as a primary guide wire over which a balloon catheter or other interventional device can be inserted into the artery.