Threshold measurements using stimulating electrodes of different materials in the skeletal muscles of cats

In the skeletal muscle of cats, semispherical stimulating electrodes having a radius of 1.2 mm deliver a mean threshold current of 0.15 mA, corresponding to 1.7 mA/cm2. These values are doubled within a period of four weeks after chronic implantation. In the case of non-polarizable electrodes the mean threshold voltage increases from 108 mV to 171 mV. The lowest individual values range between 50 mV and 60 mV at the time of implantation. The highest value is around 500 mV after four weeks. The high values have been observed with strongly polarizing ELGILOY electrodes. The chronic threshold energies vary between 3 x 10(-8) Ws for activated vitreous carbon electrodes and 17.5 x 10(-8) Ws for ELGILOY electrodes. There are two reasons for the low threshold energy of activated vitreous carbon electrodes. One reason is their low polarization, and the other is their better compatibility. Connective tissue layers with a thickness between 25 micron and 50 micron are found around well healed carbon electrodes.