An Amperometric Technique for Recording Ascorbate Dilution Curves and Blood Flow Pulses.

In 1960 Leland Clark reported his discovery that the concentration of ascorhic acid injected into the blood stream could be measured continuously with a platinum electrode and amperometric apparatus. His communication was important because it gave cardiologists an innocuous indicator and a simple method for recording dilution curves within the circulation. The principle of the method is that a constant potential difference is maintained between a platinum electrode introduced into the blood stream and a reference electrode placed on the skin. When injected vitamin C reaches the platinum electrode some ascorbate ions are oxidized, additional electrons are released, and the current increases proportionally to the concentration of ascorbate ions at the surface of the electrode (Frommer, Pfaff, and Braunwald, 1961). The apparatus developed here for maintaining constant voltage allows the changes in current to be recorded simply and inexpensively with the later D.C. stages of commercial electrocardiographs (Hay, Hepburn, and Nixon, 1963). The apparatus also gives an estimate of the pattern of pulsatile blood flow (Pfaff, Frommer, and Morrow, 1960), and this may be recorded simultaneously with the pressure pulse at cardiac catheterization. The purpose of this communication is to report experience with the ascorbate dilution technique, and to suggest that the blood flow pulse is of value in the investigation of patients with heart disease.