Mitochondrial oxygen monitoring with COMET: verification of calibration in man and comparison with vascular occlusion tests in healthy volunteers.

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) measurement, incorporated in the COMET. In contrast to most textbooks, relatively high average mitoPO values have been reported. The first aim of this study was to verify the validity of the COMET calibration for mitoPO measurements in human skin. The second aim was to compare the dynamics of mitoPO 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 was reached by local application of cyanide. MitoPO was compared to the arterial oxygen partial pressure (PaO). Secondly, for deoxygenation kinetics we compared COMET variables with the LEA O2C, SenTec OxiVenT™ and Medtronic INVOS™ parameters during a vascular occlusion test. 20 healthy volunteers were recruited and resulted in 18 datasets (2 times 9 subjects). The lowest measured mitoPO value per subject had a median [IQR] of 3.0 [1.0-4.0] mmHg, n = 9. After cyanide application the mitoPO was 94.1 mmHg [87.2-110.9] and did not differ significantly (n = 9, p = 0.5) from the PaO of 101.0 [98.0-106.0] mmHg. In contrast to O2C, OxiVenT™ and INVOS parameters, mitoPO declined within seconds with pressure on the probe. The kinetics from this decline are used to mitochondrial oxygen consumption (mitoVO). This study validates the calibration of the COMET device in humans. For mitoVO measurements not only blood flow cessation but application of local pressure is of great importance to clear the measurement site of oxygen-carrying erythrocytes.