A new measuring device for non-invasive determination of oxygen partial pressure and oxygen conductance of the skin and other tissues.

摘要

About fifty percent of the oxygen consumption of the skin is supplied by diffusion through the surface. This portion of the skin oxygen supply becomes of high importance in case of arterial occlusion. The oxygen permeation coefficient (P) of the upper layers and the oxygen pressure field within the skin determine the diffusive oxygen uptake from the outside. To our knowledge, the permeation coefficient (P) until now was only estimated by indirect methods of little practicability (Baumberger et al., 1951; Eberhard et al., 1978). An oxygen partial pressure of the skin is conventionally measured by modified CLARK type electrodes. A disadvantage of this so-called transcutaneous electrode is its oxygen consumption and the fixed coupling of the consumption with the oxygen pressure to be determined. Therefore the measurement always induces a systematic error (the so-called stirring effect) which depends, among other factors, on the oxygen availability of the skin under the electrode. The new device combines a consumption-free oxygen partial pressure detector on the basis of luminescence quenching by oxygen with an independently working specific oxygen consumer realized by an active galvanic chain (silver-lead element). The chain permits setting any oxygen mass flow (mO2) in a certain range by varying the electrode current choosing different resistors within the electrical circuit. According to the diffusion law, the surface oxygen pressure (ePO2) being measured is a linear function of the oxygen flow (mO2) directed to the cathode: ePO2 identical to -(1/P).(mO2/A) + icPO2; A: area under the cathode. The intracutaneous oxygen partial pressure (icPO2) is a virtual quantity defined by the equation given. Only by using an active electrode different oxygen mass flows can be set and so the oxygen conductance of the upper skin layers can be assessed. First experiments on human skin in the gluteal region of an adult delivered an estimated value of the permeation coefficient (P): 2.2.10(-5) ml O2 (STPD)/(atm.s.cm2) at 42 degrees C skin surface temperature; the intracutaneous partial pressure obtained was 5.5 kPa (41 mmHg) (STPD: "standard temperature pressure dry" conditions of the gas). At 42 degrees C skin temperature no burning occurs. The determined O2-conductance is in the same range as estimated formerly (see above). The intracutaneous oxygen partial pressure determined seems to be a realistic value of the tissue at 42 degrees C. By in vitro measurements with technical membranes the new device and procedure was validated giving precise values of the oxygen conductance. Hence the new method may be used for calibration of the oxygen flux optode (Holst et al., 1993). The O2-permeation coefficient (P) could be an important parameter for evaluating dermatological applications (which attempt to increase P) in the treatment of local dermal oxygen deficiency. The intracutaneous oxygen partial pressure found is a reasonable value for a surface temperature of 42 degrees. Because of the independence of the O2-partial pressure determined and the O2-consumption the new device exhibits no stirring effect and it provides more insight into the limitations of conventional transcutaneous oxygen measurement.