<P> To see the relative affinities of each successive oxygen as you remove / add oxygen from / to the hemoglobin from the curve compare the relative increase / decrease in p (O) needed for the corresponding increase / decrease in s (O). </P> <P> The strength with which oxygen binds to hemoglobin is affected by several factors . These factors shift or reshape the oxyhemoglobin dissociation curve . A rightward shift indicates that the hemoglobin under study has a decreased affinity for oxygen . This makes it more difficult for hemoglobin to bind to oxygen (requiring a higher partial pressure of oxygen to achieve the same oxygen saturation), but it makes it easier for the hemoglobin to release oxygen bound to it . The effect of this rightward shift of the curve increases the partial pressure of oxygen in the tissues when it is most needed, such as during exercise, or hemorrhagic shock . In contrast, the curve is shifted to the left by the opposite of these conditions . This leftward shift indicates that the hemoglobin under study has an increased affinity for oxygen so that hemoglobin binds oxygen more easily, but unloads it more reluctantly . Left shift of the curve is a sign of hemoglobin's increased affinity for oxygen (e.g. at the lungs). Similarly, right shift shows decreased affinity, as would appear with an increase in either body temperature, hydrogen ions, 2, 3 - bisphosphoglycerate (2, 3 - BPG) concentration or carbon dioxide concentration . </P> <Table> <Tr> <Th> Control factors </Th> <Th> Change </Th> <Th> Shift of curve </Th> </Tr> <Tr> <Td> Temperature </Td> <Td> ↑ </Td> <Td> → </Td> </Tr> <Tr> <Td> ↓ </Td> <Td> ← </Td> </Tr> <Tr> <Td> 2, 3 - BPG </Td> <Td> ↑ </Td> <Td> → </Td> </Tr> <Tr> <Td> ↓ </Td> <Td> ← </Td> </Tr> <Tr> <Td> pCO </Td> <Td> ↑ </Td> <Td> → </Td> </Tr> <Tr> <Td> ↓ </Td> <Td> ← </Td> </Tr> <Tr> <Td> Acidity (H) </Td> <Td> ↑ </Td> <Td> → </Td> </Tr> <Tr> <Td> ↓ </Td> <Td> ← </Td> </Tr> </Table> <Tr> <Th> Control factors </Th> <Th> Change </Th> <Th> Shift of curve </Th> </Tr>

As acidity increases hgb's affinity for o2