20 or less of the cross sectional area of the vessel minimizing the obstruction of flow within the vessel allows the sensor to remain secured in position in a vessel without creating significant impact to the flow within the vessel in one embodiment as shown in fig1 and 2 the body of the intracorporeal device 6 coupled to the fixation loops 9 has a width of about 0 5 to about 4 mm a height of about 0 5 to about 4 mm and a length of about 0 5 to about 25 mm examples of such devices are disclosed in commonly owned patents u s pat no 6 855 115 and in co pending commonly owned applications ser nos 10 054 671 10 886 829 10 215 377 10 215 379 10 943 772 incorporated herein by reference one method of deploying and fixing an implant assembly according to this invention is described below the delivery system consisting of catheter 8 and sensor 6 is loaded into the vessel introducer 3 and navigated to the deployment site the delivery system length can be increased or decreased according to standard practice depending on the access site chosen in one embodiment the deployment site is a vessel and may be any artery or arteriole in the pulmonary artery vasculature after the assembly is oriented to a preferred orientation the sensor 6 is deployed by retracting the guidewire 4 so that it no longer is threaded through the fixed loop 5 of.