Mark Wefers Bettink

Verification of calibration in man and comparison with vascular occlusion tests in healthy volunteers with COMET 4 69 3. Results A total of 20 healthy volunteers were recruited and provided informed consent. Of the 20 volunteers 10 underwent the entire study protocol. One subject dropped out due to beta-thalassemia that was missed during the inclusion procedure. The first 10 inclusions (session 1) resulted therefore in 9 complete datasets. Analysis of this first dataset showed that cyanide application led to unmeasurable delayed fluorescence in all but 1 subject. This unforeseen result was analyzed in cooperation with the manufacturer of the COMET device. It appeared to be caused by the relatively long photomultiplier gate duration in comparison to the very short delayed fluorescence lifetimes after cyanide application, illustrated in Figure 2. PMT Gating period τ short, low signal intensity τ long, high signal intensity Time (μs to ms) PMT output (Volts) Laser pulse Figure 2 : This illustration shows the decrease in signal intensity measured by the photomultiplier (PMT) with short lifetimes (several μs). If the lifetime is short the oxygen tension is high. The laser pulse (green) is followed by a PMT gating period (gray) to protect the PMT from prompt fluorescence. At the PMT most of the short lifetime signal intensity (red) will be lost. In low oxygen tension and thus a long lifetime (orange) the signal intensity will hardly be influenced by the PMT gating period. A temporary change in the firmware of the COMET, kindly supported by themanufacturer, was suggested and used to overcome this problem. Therefore, a second series of measurements (session 2) with the cyanide cream was performed in 10 subjects. One subject had insufficient signal quality after the baseline measurement. This resulted in 9 datasets of new volunteers in the second session. A flow diagram of the inclusions is shown in Figure 3.