Cathodic stimulation

Walker Cederholm 1907 Established role of oxygen in corrosion as a cathodic stimulator... 

Vulnerability to ventricular arrhythmias. There is the theoretical risk of ventricular fibrillation whenever a pacemaker stimulus is delivered into the vulnerable period of the ventricle. Experimentally, the ventricular fibrillation threshold is lower with bipolar stimulation than with conventional unipolar cathodal stimulation. Despite these laboratory observations, no clinical differences between permanent unipolar and bipolar systems have been reported with respect to the risk of inducing ventricular arrhythmias. 

System-specific procedural requirements for electrochemical studies of CMP systems have been discussed in the literature, and are briefly noted later in the context of experimental results for individual cases. In this regard, the ASTM guides for corrosion and polarization measurements can serve as a comprehensive guideline for the analysis of corrosion parameters (ASTM, 2004, 2010). As noted in the context of Figure 3.2, additive induced shifts in the OCP can occur by multiple mechanisms, and a given OCP shift can arise from a number of reasons for instance, an upward shift in Eoc can occur from anodic passivation or from cathodic stimulation of the same system. For this reason, full Tafel plots should be used to adequately interpret the mechanisms of OCP variations. 

Oxygen action as cathodic stimulator Walker, Cederholm... 

Anodic/cathodic stimulation It has been demonstrated experimentally that in the case of electrical stimulation of peripheral nerves, cathodic stimulation has a lower threshold (less current required) than anodic stimulation. This experimental result can be directly explained by plotting Veq for a cathodic and anodic electrode (1 mA) located 1 cm away from an 10-/um unmyelinated fiber (Figure 28.7). The maximum value of Veq for anodic stimulation is 0.05 mV at the two sites indicated by the arrow. However, the maximum depolarization for the cathodic electrode is significantly larger at 0.2 mV with the site of excitation located directly underneath the electrode. In special cases, such as an electrode located on the surface of a cortex, cathodic stimulation can have a higher threshold [Ranck, 1975]. 

Anodal surround block As shown by the current-distance relation, the current amplitudes required for excitation decrease with distance. This is not entirely true for cathodic stimulation. Cathodic stimulation produces membrane depolarization underneath the electrode and membrane hyperpolarization on both sides of the electrodes (Figure 28.7b). As the current amplitude is increased, the hyperpolarization also increases and can block the propagation of the action potential along the axon. This effect is known as anodal surround block and is shown in Figure 28.10b. It is possible to identify three regions around the electrode each giving different responses. There is a spherical region close to the electrode (1) in which no... 

FIGURE 28.9 Current-distance relationship for monopolar cathodic stimulation of myelinated axons. The distance between the axon and the electrode is plotted as a function of current threshold amplitude for many experiments from several authors. The dashed line shows the current-distance relation calculated for 10-/ttm fiber stimulated with a 200-/itsec pulse. (From Rattay F. IEEE Trans. Biomed. Eng. 36 676-681,1989. With permission.)... 

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