Electrode-oxygen consumption and its effects on tissue-oxygen tension. A study by mass spectrometry.

A theory for the mechanism of electrical bone stimulation proposes that passage of an electric current reduces the local PO2 and raises the pH near the cathode, thereby creating a favorable environment for osteogenesis. To study the effects of electric current passage on the PO2, PCO2 and pH in the vicinity of the electrodes in vivo, a wire electrode spiralled around the catheter of a clinical mass spectrometer was placed in dog muscle. Electrodes were made of stainless steel or platinum. With a cathode located in the tissue, a 20-microA direct constant current caused a drop in PO2 of 5-10 mmHg and a drop in PCO2 of 2-6 mmHg, both reaching plateaus again within five to 20 minutes. The time required to reach this new equilibrium was shorter for platinum than for stainless steel. When the electric current was turned off, PO2 and PCO2 reversed to their original values. Because of the high buffer capacity of tissue, it is highly unlikely that 20-microA current would induce a change in pH.