Tissue Factors Continued
As active muscles exhibit all these features, the delivery of oxygen to them is greatly assisted. Also 2,3-DPG is generated during metabolism, so is at a higher concentration at the peripheral tissues.
The graph illustrates the effects of 2,3-DPG levels on the O2Hb curve.
By preferentially binding to deoxyhaemoglobin, it stabilises the reduced state Hb, making it harder for O2 to bind Hb and more likely to be surrendered to adjacent tissues.
The above processes produce a rightward shift of the curve. The shift in the oxygen dissociation curve as a result of changes in PaCO2 is known as the Bohr Effect. At the alveolar level the reverse enables O2 to saturate the RBCs and thus perpetuate the cycle.
An indication of the amount of shift of the oxygen dissociation curve can be gained from checking the P50.
The P50
This is the partial pressure of oxygen required to saturate 50% of the haemoglobin. It is normally around 3.6 kPa and is often provided with the blood gas result.
The graph illustrates the differences between adult and fetal haemoglobin.
Learning bite
A rise in PaCO2, hydrogen ions and temperature shifts the haemoglobin dissociation curve to the right. A rise in the P50 indicates a shift in the haemoglobin dissociation curve to the right. A fall in the P50 indicates a shift in the haemoglobin dissociation curve to the left.