QS Study

Properties of Oxygen-Hemoglobin Dissociation Curve

The Oxygen – Hemoglobin dissociation curve is a significant implement for considerate how our blood carries and releases oxygen. Particularly, the Oxygen-Hemoglobin (O2 –/ Hb) dissociation curve relates oxygen saturation and incomplete pressure of oxygen in the blood (PO2) and is determined by what is called “hemoglobin’s affinity for oxygen,” that is, how readily hemoglobin acquires and releases oxygen molecules from its surrounding tissue.


  • Ordinate: Percent saturation of Hb with Oxygen.
  • Abscissa: Partial pressure of Oxygen (PO2).

Past: The Oxygen – Hemoglobin dissociation curve has three parts.

(1) Flat part, (2) Oblique part, and (3) Steep part.

Fig: Oxygen-Hemoglobin Dissociation Curve

(a) Flat part

  1. This part of the curve is for lung.
  2. PO2 is from (100 – 70) mmHg.
  3. Percent saturation of Hb of this part is –

So, 30 mmHg pressure change. The percent saturation of Hemoglobin changes only (97.5 – 92.7)% = 4.8%.

Importance: It is difficult to maintain the constant pressure inside the lungs. So it is necessary to keep the percent saturation of Hemoglobin constant inspite of wide range variation of PO2 in lungs to continue normal any generation of blood.

(b) Obligue part

  • This part for blood
  • It is from Po2(70 – 40) mmHg.
  • Percent saturation of Hemoglobin of this part is –

So, for 30 mm-Hg PO2 change percent saturation of Hemoglobin is only (92.7 – 75)% -17.7

(c) Steep part

  • It is for the cells
  • It is from PO2 (40-10) mm-Hg
  • Percent saturation of this part is.

So, for 30 mm-Hg pressure change the percent saturation charge is (75 – 13.54)% = 61.5%.

Importance: It is necessary to release Oxygen in the tissue, so only 30 mm Hb pressure change because a wide range of change in percent saturation facilitating the release of Oxygen in the tissue from the Hb.

Clinical Application

  • at present, there is not enough data to support manipulation of O2-Hb curve to improve O2 delivery
  • if arterial PO2 is critically low then O2 binding in the lungs may be impaired by a shift to the right, this may seriously impair tissue oxygenation