Mark Wefers Bettink

Chapter 4 68 with a frequency of 1 Hz. The O2C, INVOS, and SenTec OxiVenT all collected data during arterial occlusion to determine the oxygen level and consumption, as well as carbon dioxide (CO 2 ) accumulation in the measurement volume. In this setup no pressure was applied to the COMET skin sensor in order to be able to compare the deoxygenation rates of the different measurements. The mitoVO 2 measurement was done with the following procedure; after a stationary measurement of 10 seconds direct pressure on the COMET Skin Sensor probe was applied. This halted the microcirculation, and with it oxygen delivery to the measured tissue volume. The mitoVO 2 was measured directly after local occlusion of the oxygen supply by a linear fit of mitoPO 2 . This simple procedure created reproducible stop- flow conditions and induced measurable oxygen consumption rates, consequential to a cessation of microvascular oxygen supply and ongoing cellular oxygen consumption. MitoPO 2 was measured before, during and after application of pressure at an interval of 1 Hz. 2.3 Statistical analysis and software Software version v.016.5b.184 of COMET was used, during the cyanide measurements, the adjusted timing software was used. Statistical analysis and visualization were done with R version 3.4.2 [17] and GraphPad Prism 6. MitoPO 2 and Arterial Blood Gas were compared using a two sided Wilcoxon-Mann-Whitney U-test. Significance was determined by p-values < 0.05. Values are given as median and interquartile ranges or stated otherwise. The average of the last 3 MitoPO 2 values measured before pressure was applied were used as a baseline. Linear slope comparison (as measure for the deoxygenation rate, or oxygen disappearance rate) between COMET, INVOS, SenTec OxiVenT was performed with GraphPad Prism linear regression model from the descending part of the data. MitoVO 2 linear fit was done with LabVIEW (Version 13, National Instruments, Austin, TX, USA) with the first 4 samples after pressure had been applied by the sensor to compare mitoVO 2 with previous published results [10]. To visually compare the oxygenation decline rate between the devices the data is transformed into z-score (datapoint – mean)/ standard deviation.