Over the last eighteen years, a considerable amount of evidence has been accumulated 1-a which shows that thrombosis occurs via an electrochemical mechanism and depends on the electrochemical interracial characteristics of the blood vessel, blood cells and prosthetic material. In a recent study 4 wires covering a wide range in the electromotive series were implanted into the carotid and femoral arteries of dogs for periods ranging from 30 to 90 minutes, and their potentials were measured. The wires were then removed and examined for thrombus formation. A distinct correlation between the spontaneous (open circuit) potential of the implanted wire and the tending for thrombus formation on it was observed. Metals which exhibited spontaneous potentials negative vs. the normal hydrogen electrode remained clean, while the wires of metals which registered positive potentials were thrombosed. In controlled-potential measurements on Pt, thrombus formation was shown to occur both in vivo and in vitro if the potentials were above 0 to 100 mV vs. the NHE. When potentials fell below this value thrombosis rarely occurred 2 . Implantation of tubes 2,5 which replaced arterial or venous segments and of heart valves 6 ,7 constructed of various metals and alloys confirmed the dependence of thrombus formation on the interfacial potential of the material in contact with blood.
From the work to date, it appears that thrombus formation is associated with the potential-dependent adsorption of one or more components of blood on the prosthetic material. In the case of conducting surfaces, information concerning adsorption of species from solution may be obtained from double-layer capacitance measurements 8 . Thus any changes occurring at the interface (e.g., adsorption of proteins on electrode, platelet adhesion) may be detected by a change in the capacity.
Recently, a capacitance meter was developed 9 which provides a quick response output signal proportional to the magnitude of the capacity, which can be fed into a recorder and measured as a function of potential and/or time. Some preliminary results obtained by this technique are shown in Figs. and. The capacitance vs. potential plot for gold in normal saline is shown in Fig. together with a curve for thrombus-covered gold electrode in the same solution. As expected, the formation of a thrombus deposit on the electrode surface alters substantially the shape of the C vs. V plot and generally causes a decrease in capacitance at each potential. These changes can be used to detect thrombus formation on a conducting surface in vivo without having to remove the implanted prosthesis. Fig. shows similar C vs. V plots for an initially clean gold electrode immersed