Mark Wefers Bettink

A monitor for Cellular Oxygen METabolism (COMET): monitoring tissue oxygenation at the mitochondrial level 3 51 2.5 Skin sensor The biocompatible housing (70x20x20mm) of the Skin Sensor, shown in figure 3, holds two optical fibers; the excitation and the detection fiber. A flexible metal tube protects the vulnerable optical fibers against external mechanical forces. The optical design of the sensor can collect light at approximately a right angle to the sensor cable. The light emitted by the sensor is divergent and safe for eyesight at any distance. Ambient light entering the detection path might overload or even damage the photomultiplier tube. For protection, a photodiode in the Skin Sensor determines the ambient light before each measurement. Sensor temperature, used as an approximation of skin temperature, is measured with an electrical resistive sensor. Fig. 3 Detailed view of skin sensor 2.7 Oxygen-consumption measurement The COMET provides the opportunity for measurements in dynamic situations by taking a series of 120 samples of the mitoPO 2 acquired at 1Hz. This can be used to determine the oxygen disappearance rate (ODR) and reperfusion. Typically, mitochondrial oxygen availability is measured for 10-20 seconds in an undisturbed and stable situation. Subsequently light pressure is applied with a hand onto the sensor, to give occlusion of the microcirculation and stop local blood flow in the measurement volume, for about 45 seconds. After these 45 seconds the pressure is released and restoration of microcirculatory blood flow and mitochondrial re-oxygenation will appear. Previously, we have described the fundamental principles behind the technology and have provided a working implementation of the technique for mitoVO 2 measurements in vivo [14]. In summary, the ODR is generally dependent on two factors; oxygen consumption