During a zero flow event, such as an arterial occlusion, you may encounter blood perfusion units (BPU) dropping into negative values. A slightly negative BPU reading (for instance, -10 BPU ) is equivalent to zero BPU on the IN191 Blood Flowmeter's 5000 BPU range, and well within the unit's accuracy specification.
If you have further questions, please contact ADInstruments Technical Support.