Transcutaneous permeability

A well-designed series of AA-disubstituted 2-aminoethyl and 3-amino-propyl esters of indomethacin (8.9, R = OH) was examined for its chemical and enzymatic (human plasma) rates of hydrolysis [40]. The 3-(diethylami-no)propyl ester had a transcutaneous permeability coefficient ca. 100-times... 

Transcutaneous measurement of partial pressures is based on the gas permeability of human skin. An electrochemical sensor is placed on the skin which is heated to increase arterial blood in superficial blood vessels [1]. 

The value of the partial pressure measured at the skin surface depends in a complex way on blood partial pressure, constitution of the skin, local perfusion, metabolism in the associated tissue, cardiac output, and application temperature. An increased temperature of 43 °C raises the gas permeability and expands the capillary vessels of skin which are filled with more artial blood. The local hyperemia has the disadvantage of limiting the application time at a certain site. Assuming stable circulation conditions, transcutaneously measured values correlate with arterial partial pressure by a factor of 1.2 (neonates) to 1.0 (small children) [1]. The measured value for adults proved to be very unreliable. In the case of unstable conditions or shock with a reduction of peripheral blood flow, the transcutaneous value drops very early. Inconvenience in routine use is caused by long preparation times of the sensor, the need for periodic membrane changes, the long run-in time of freshly prepared sensors, the necessity for periodic calibrations and the slow response time to changes in partial pressure. 

In 1954 Leland Clark demonstrated that a platinum cathode would measure the oxygen concentration of blood when it and a reference electrode were covered by an oxygen permeable membrane. Later in that same year Stow and Severinghaus showed that carbon dioxide could be estimated in blood with a glass electrode fitted with a gas permeable membrane. In the seventies the Huchs demonstrated that mechanical adaptations of these devices could be utilized to provide transcutaneous (non-invasive) measurement of arterial blood gas concentration if the skin area surrounding the sensor was heated to 44 - 45°C. 

Mitsubayashi et al. (2003) developed a wearable and flexible oxygen sensor with membrane structure, constructed using microfabrication techniques, and containing a nonpermeable sheet and a gas-permeable membrane with platinum- and Ag/AgCl-electrodes. The sensor device, applied to the skin surface of healthy male volunteers with no history of skin diseases, allowed the safe monitoring, by CV, of the transcutaneous... 

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