What is the oxyhemoglobin dissociation curve and why is it important?
• The Oxyhemoglobin dissociation curve describes the non-linear tendency for oxygen to bind to hemoglobin: below a SaO2 of 90%, small differences in hemoglobin saturation reflect large changes in PaO2 The oxyhemoglobin dissociation curve mathematically equates the percentage saturation of hemoglobin to the partial pressure of oxygen in the blood. The strange sigmoid shape of the curve relates to peculiar properties of the hemoglobin molecule itself: Hemoglobin and oxygen act a little like parents and children. When all are living at home (i.e. hemoglobin is fully saturated) then the parents dont want any to leave: but once one has flown the nest (i.e. dissociated from hemoglobin) parents find it progressively easier to let go. What this means that the conformation of the hemoglobin molecule depends on the number of molecules bound: as one molecule of oxygen becomes unbound, the affinity for the others falls [and vice-versa]. This is represented by the oxyhemoglobin dissociation curve.
