Mark Wefers Bettink

Chapter 4 62 Abstract Mitochondria are the primary consumers of oxygen and therefore an important location for oxygen availability and consumption measurement. A technique has been developed for mitochondrial oxygen tension (mitoPO 2 ) measurement, incorporated in the COMET. In contrast to most textbooks, relatively high average mitoPO 2 values have been reported. The first aim of this study was to verify the validity of the COMET calibration for mitoPO 2 measurements in human skin. The second aim was to compare the dynamics of mitoPO 2 to several other techniques assessing tissue oxygenation. Firstly, we performed a two-point calibration. Mitochondrial oxygen depletion was achieved with vascular occlusion. A high mitoPO 2 was reached by local application of cyanide. MitoPO 2 was compared to the arterial oxygen partial pressure (PaO 2 ). Secondly, for deoxygenation kinetics we compared COMET variables with the LEA O2C, SenTec OxiVenT™ and Medtronic INVOS™ parameters during a vascular occlusion test. Twenty healthy volunteers were recruited and resulted in 18 datasets (2 times 9 subjects). The lowest measured mitoPO 2 value per subject had a median [IQR] of 3.0 [1.0 – 4.0] mmHg, n=9 . After cyanide application the mitoPO 2 was 94.1 mmHg [87.2 – 110.9] and did not differ significantly (n=9, p =0.5) from the PaO 2 of 101.0 [98.0 – 106.0] mmHg. In contrast to O2C, OxiVenT™ and INVOS parameters, mitoPO 2 declined within seconds with pressure on the probe. The kinetics from this decline are used to mitochondrial oxygen consumption (mitoVO 2 ). This study validates the calibration of the COMET device in humans. For mitoVO 2 measurements not only blood flow cessation but application of local pressure is of great importance to clear the measurement site of oxygen-carrying erythrocytes.