Noninvasive Quantification of Platelet Accumulation and Release on Indwelling Venous Catheters

Abstract

An important element in the evaluation of biomaterials is quantification of the relationships and the sequence of events between blood elements, blood flow, and the foreign surface. We adapted a qualitative two-dimensional 111In-la-beled platelet imaging method to a quantitative noninvasive analysis of platelet uptake/release kinetics for infusion catheters in a canine model. Bilateral femoral vein 6 Fr. Groshong catheters (one treated with a hydroxylated siloxane to improve albumin affinity) were monitored at femoral vein sites with a GE 400T gamma camera, interfaced with a Technicare 560 image acquisition computer. The field of view was sufficiently large that all events below the diaphragm were recorded without having to move the camera. Image acquisition time was 2.5 min; images were obtained every 5–15 min for 3 hrs. Continuous recordings were obtained from bilateral ultrasonic velocity probes, attached distal to the catheter implant sites. A 5 ml blood sample was placed in the field to permit calibration of gamma emissions per pixel in terms of labeled platelet density. Signal compensation for near field capillary perfusion was performed. The two-dimensional platelet distribution was computed and displayed. Local, time dependent platelet accumulation on the catheters and adjacent vessel walls was observed. Platelet accumulation proceeded in irregular steps during the implant period. Loss of local platelet deposits was observed. Downstream reattachment of platelet emboli was inferred from simultaneous reductions and increases in local platelet densities at two catheter positions. Platelet attachment was inversely related to vein blood velocity. Differences were observed between platelet uptake and release on the treated and control catheters. These preliminary results suggest that the method is feasible for both in vivo and ex vivo evaluation of the interactions of labeled blood elements and medical devices.