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.
Only affected by PaO2, not CaO2 (so in conditions such as anemia or COHb, even though the patient's total O2 content is reduced, the periperhal chemoreceptor's are not stimulated) Not a significant response until PaO2 falls to ~60 mm Hg (corresponds to an SaO2 of 90%) A further fall results in sharp increase in VE.