Effect of Electrode Dimensions on Tissue pO₂ Measurement in vivo

Abstract

THE measurement of tissue oxygen tensions in vivo by a polarographic technique using platinum electrodes was described by Davies and Brink¹. Since then many different types of electrodes have been used, including membrane-covered electrodes which are unaffected by flow and give good calibration characteristics but are fragile and very large in comparison with cellular dimensions. Such electrodes and their characteristics have been described by Charlton², Evans and Naylor^3,4 and Naylor and Evans^5,6. Open-ended electrodes are affected by fluid movement at the exposed tip but they are easy to construct and use and can be made very small and more suitable for insertion into solid tissues. The usual electrode used for tissue pO₂ measurements has been bare-ended or collodion-covered gold or platinum electrodes, approximately 200–300µ, diameter^7–10. Cater has also used rigid needle electrodes, with fine tips¹¹. However, the tissue trauma caused by the physical act of insertion of such electrodes could probably cause fairly large quantitative errors in pO₂ measurements^12–14, and thus it was considered of interest to compare tissue pO's registered by electrodes of different dimensions. We had previously used 330µ insulated gold wire to record tissue and tumour pO₂ at ambient and raised oxygen tensions in animals^13,14. In the present work, pO₂ registered by these electrodes were compared with those registered by electrodes made from 60µ gold wire, while animals breathe air or oxygen at 4 or 5 atmospheres.