oxygen dissociation curve
oxygen dissociation curveOxygen saturation curve Physiology A curve that describes the relationship between Hb O2 saturation and tension; defined by a sigmoid curve which reflects the interaction of the 4 Hb molecules involved in O2 uptake, transport and release; a 'right shift' of the curve indicates ↓ Hb affinity for O2, as occurs in ↓ pH–ie, acidosis, ↑ temperature, ↑ PCO2, while a 'left shift' indicates ↑ O2 affinity with ↑ pH, ↓ temperature, ↓ 2,3 DPG and ↓ PCO2 Right shifts Acidosis, hyperthermia, alveolar hypoventilation, anemia Left shifts Alkalosis, hypothermia, hyperventilation, carboxyhemoglobinemia, hypophosphatemia, ↑ fetal Hb. See 2,3 DPG.
oxygen dissociation curvea curve derived from plotting the percentage saturation of blood with oxygen, against the oxygen tension (the oxygen exchange).
The curve is S-shaped and shows that HAEMOGLOBIN has a high affinity for oxygen.Blood can become saturated at relatively low oxygen tensions, but a small drop in oxygen tension brings about a big fall in the saturation of the blood. If tissues use up oxygen, then haemoglobin responds by giving it up.
Where CO2 is present, haemoglobin has to be under higher oxygen tension in order to become fully saturated. However, under these circumstances it releases O2 at higher oxygen tensions. CO2 affects the efficiency of oxygen uptake by haemoglobin but increases its efficiency in releasing it. The oxygen-carrying capacity of blood is also affected by pH (see BOHR EFFECT).