Mark Wefers Bettink

A monitor for Cellular Oxygen METabolism (COMET): monitoring tissue oxygenation at the mitochondrial level 3 53 3. Results 3.1 Oxygen-consumption measurement A typical example of an oxygen-consumption measurement on the healthy volunteer, is shown in figure 4. Mean mitoPO 2 (t 0 - 19 ) gave a baseline mitoPO 2 of 22.7 ± 2.1 mmHg (mean ± SD). After 20 seconds direct pressure with the probe was given to occlude microvascular blood flow in the skin. The available oxygen was consumed and resulted in an oxygen disappearance rate of 6.3 mmHg.s -1 . When the pressure was released and direct oxygen recovery up to 60-70 mmHg in mitoPO 2 was seen. At 120 seconds the mitoPO 2 returned to baseline values. Fig.4 A typical dynamic measurement of mitochondrial partial oxygen pressure (mitoPO 2 ) by COMET measurement system. A sample of 120 seconds is shown. In the first 20 seconds the baseline was determined, afterwards light pressure was applied on the sensor to stop microcirculation and the oxygen disappearance rate (ODR) was measured. At 60 seconds pressure was released. 3.2 Incidental finding during ongoing clinical study In one of the measured patients during an ongoing feasibility study in neurosurgery patients, clonidine was given intravenously due to persistent hypertension. Clonidine is a central inhibitor of noradrenergic neurotransmitter transmission but also a peripheral a1-agonist. Given in a short period of time clonidine leads to initial peripheral vasoconstriction, followed by a slow onset of vasodilatation. In this particular case 150 microgram of clonidine was given as a bolus application. A direct onset effect of vasoconstriction on flow and velocity but not on capillary venous oxygen saturation (SO 2 ) was seen as measured by O2C figure 5. Flow decreased by 44% and velocity by 16%. Although SO 2 did not change, a transient drop in mitoPO 2 was measured with the COMET. MitoPO 2 dropped from a steady state of 48 mmHg to 16 mmHg. After the fast clonidine