Mark Wefers Bettink

Chapter 4 78 a penetration depth of several cm. Since O2C and INVOS measure deeper in the tissue, and thus in a different tissue compartment, the decline in oxygen saturation represents a larger measurement volume. After the occlusion an equilibrium emerges between the available oxygen, mainly dependent on the concentration and amount of arterial and venous hemoglobin available in the vessels, and mitochondrial respiration. It is not possible to push away or largely reduce the number of erythrocytes in the infra- red measurement volume. A large measurement volume that contains erythrocytes without the ability to reduce the oxygen buffer results in a slower decrease in saturation. When performing a dynamic measurement with the COMET local pressure with the Skin Sensor leads to largely eliminating the available erythrocytes from the microcirculation and therefor the dynamic measurement may be less dependent on the availability of the oxygen buffer. 5. Conclusion This study shows that mitochondrial oxygen partial pressures measured with Pp-IX lifetime technique are comparable to the arterial PaO 2 during blockade of mitochondrial respiration with topical application of cyanide. Therefore, this study demonstrates that the calibration of COMET device, originally determined in animal experiments, is valid in human cutaneous mitoPO 2 measurements. For mitochondrial oxygen consumption measurements not only blood flow occlusion, but applying pressure on the COMET Skin Sensor is of great importance to clear the measurement site of available oxygen-carrying erythrocytes. Without a technique to eliminate this oxygen buffer the consumption measurement underestimates the actual mitochondrial oxygen consumption.