Oxyhemoglobin Dissociation Curve

The flat portion of the normal curve at the top of the graph is sometimes called the arterial portion and represents partial pressure changes of oxygen between 60 and 100 mm Hg.

Changes between these two values do not significantly affect the percent of saturation of hemoglobin. The steep part of the curve occurs after the partial pressure of oxygen drops below 60 mm Hg. It represents the rapid dissociation of oxygen from hemoglobin. During this phase there is rapid release of oxygen for diffusion into the cells.

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When the curve shifts to the left, hemoglobin has an increased affinity for oxygen and releases less to the tissues.

Conditions that cause this include acute alkalosis, decreased PCO2, decreased temperature, low levels of 2,3-DPG, carboxyhemoglobin, methemoglobin, and abnormal hemoglobin.

 

Left Shift - shows an increased hemoglobin affinity to oxygen. It is easier to load oxygen but difficult to unload it.

When the curve shifts to the right, hemoglobin has a decreased affinity for oxygen.

Conditions that cause this include acute acidosis, high PCO2, increased temperature, high levels of 2,3-DPG, and abnormal hemoglobin.

 

Right Shift - shows a decreased hemoglobin affinity to oxygen. It is difficult to load the oxygen, but easy to unload the oxygen.