SUMMARY1. The extracellular pH value in the dermis of human skin (skin pH) was measured in vivo using glass micro-electrodes. They were found to be both reliable and accurate.2. The mean value of skin pH measured in the legs of forty different volunteers was found to be pH 7-54 ± 0-09 (S.D.). No difference in skin pH was observed between males and females, or in different regions of the limb.3. Local reductions in skin surface temperature in ten subjects caused an increase of pH 0-023 + 0 007 per TC fall.4. A 20 min period of tourniquet ischaemia in twenty volunteers induced a fall in skin pH of 0-13 + 0-05 units.5. Hyperventilation during a 10 min period of breathing 10 % 02 in N. caused an increase of pH 0-04 + 0-02 in the skin of healthy subjects.6. Skin pH fell to a value 0-02 + 0-02 units below normal 10 min after the hypoxic period, suggesting the presence of excess lactate.7. Skin pH results compared well with blood gases and pH values of arterialized samples taken during hypoxia.8. It was concluded that the system was suitable for clinical trials.

Sixteen volunteers were tested when smoking their own brand of cigarettes normally and when smoking half their usual number of cigarettes. While smoking half their usual amount the subjects changed their inhalation behaviour. Over this period the percentages of carboxyhaemoglobin were not significantly different from steady-state values whereas plasma nicotine concentrations rose significantly. With the reduction in cigarettes there were significant falls in haemoglobin concentration, packed cell volume, and red cell count.These findings suggest that the advice given to patients to smoke fewer cigarettes should be accompanied by a warning against increasing inhalation. Patients who say that they have reduced their smoking but who have unaltered carboxyhaemoglobin concentrations should not be discredited.

Oxygen inhalation induced changes in the skin as measured by t ranscu taneous oxymetryWhen the rate of change of Ptc0, during oxygen inhalation was greater than 9 rnmHglmin all below knee amputations healed; all 4 failures were found to have values < 9 mmHg/min while only one patient with a value of < 9 mmHg/min healed a below knee amputation. This study shows that low Preo, values are a poor indication ofhealing potential. A more reliable index of skin viability is provided by the dynamic measurement oj Ptco, changes during oxygen inhalation. The addition of an oxygen inhalation test, when making Prco, measurements, greatly enhances the applicability of the technique in the assessment of the oxygen supply to the skin.

The reduction of peripheral blood flow, which occurs during shock or in patients with occlusive arterial disease of the lower limb is accompanied by an increase in hydrogen ion activity in tissue cells. If this change could be measured, it could possibly be used as an indicator of tissue perfusion in such patients. Investigations have been carried out into various pH microelectrode designs in order to construct one which could be used clinically to measure extracellular pH changes in skin. Experiments with antimony and externally insulated glass micro-electrodes demonstrated that these were unsatisfactory for the purpose. The successful design was insulated internally by means of a glass to glass fuse. It was robust, stable, sensitive and had a fast response time. Use of the electrode in normal volunteers produced reproducible skin pH values and demonstrated the feasibility of the system. Preliminary results using the micro-electrodes in patients indicate their possible application to the assessment of peripheral vascular disease, and to the monitoring of patients under intensive care.

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