Hemoglobin fully saturates with O2 at a PO2 of 100 mm Hg, the value found in the alveoli. So systemic arterial blood is carrying its full oxygen load. So systemic venous blood is a store of O2, for use in emergencies. Or develop an experiment, using the following information. Chemoreceptors only monitor PO2 and pH, not PCO2.
Cardiac output is a good variable for showing changes in cardiovascular performance.
The kidney, however, may be a slower to respond. Part of the reason for the weak response is that hyperventilation, induced by low oxygen, causes a fall in PCO2 and rise in pH, these changes inhibit the hyperventilation. To answer, you have to know the barometric pressure there, which depends upon altitude. But over days and weeks, other changes occur.