Simultaneous Measurement of Liquid Velocity and Oxygen Tension with Catheter-Tip Electrodes - The Dual Cathode Polarographic Method

The application of a dual-cathode catheter system to the simultaneous measurement of oxygen tension (pα) and velocity (V) has been studied under conditions similar to those in human arteries. The catheter tip contained a large silver electrode (16 mm
²
) and a small silver electrode (0.035 mm
²
) which were connected to a common polarizing power supply and external silver/silver chloride reference anode (774 mm
²
). The 2 mm diameter catheter was centered in a 6.4 mm diameter tube through which flow of buffered physiologic saline solution at various oxygen tensions from 154 to 736 torr was metered at velocities of 1-67 cm/s. At a fixed velocity, the limiting current outputs from both the small and large cathodes were linear with pα. Membrane-coated catheters exhibited velocity-insensitive outputs from the small cathode whenever V 5 cm/s. The large cathodes were always flow-sensitive, but the degree of sensitivity depended upon the membrane thickness. Experiments with bare large electrodes indicated that the greatest sensitivity possible with the present cathode geometry is a relative current increase of 124 percent over a velocity range of 5-67 cm/s.