Therefore, your PR interval may or may not be short and I wouldn't worry until you receive a full report. The PR interval is short in children and lengthens as we get older. A normal value in adults is 120 to 200 milliseconds. It is however shorter than 120ms in approximately 2 to 4% of the adult population.
It is SaO2 that measures oxygen saturation of hemoglobin, and it should be clear that it depends on the partial pressure of arterial oxygen. If PaO2 drops, there's less dissolved oxygen, and therefore less saturation of hemoglobin with oxygen.
-2O means 2 moles of O. The 2 in this case is a coefficient. -O2 means oxygen in its standard state. The 2 in this case is a subscript. now to describe a reaction using words, take this equation for example 3 NaBh4 + 4 BF3 -----> 2B2H6 + 3NaBF4 3 moles of NaBh4 plus 4 moles of BF3 make 2 moles of 2B2H6 and 3 moles of 3NaBF4