Oxyhemoglobin Dissociation Curve Exercise
The standard P50 value of adult hemoglobin is 26.8 mm Hg. Other points on the curve, such as the average venous point and points for 80% and 90% oxygen saturation, may also be clinically useful.
A rightward shift causes little change in conditions for loading oxygen cylinder price (essentially the same Sao2 at Po2 of 100 mm Hg). Still, it allows more significant amounts of oxygen to dissociate from hemoglobin in the tissues. This improves tissue oxygenation.
Carbon dioxide and metabolic acid shift the oxyhemoglobin dissociation curve rightward, whereas alkalosis shifts it leftward.
Fetal hemoglobin is left-shift, an adaptation uniquely suite to placental physiology. Oxygen in arterial blood is bound hemoglobin and dissolve in the plasma.
The blood oxygen content is the sum of the two forms. Although amounts of dissolved oxygen are relatively trivial at normal Po2 levels, at high Fio2, dissolved oxygen can be physiologically and clinically significant.
Although under normal conditions, only a fraction (25%) of the oxygen on hemoglobin is use, That can use all of the added dissolved oxygen added while giving supplemental oxygen.
Oxygen is primarily transported in red blood cells, attached to hemoglobin molecules throughout the body. Oxygen is also dissolve directly in the bloodstream, but this dissolved fraction contributes little to the total amount of oxygen carried in the bloodstream.
Henry’s Law states that the dissolved fraction is proportional to the atmospheric pO2. But the solubility of oxygen is so low that only 3ml O2/L of blood is dissolve at atmospheric oxygen tension. Therefore, hemoglobin carries 98% of the oxygen in the blood in the protein-bound form, approximately 197 ml/L.
It is essential to differentiate between pO2 (mm Hg, the dissolved fraction). Oxygen saturation (% of hemoglobin occupied), and O2 content (expressed as a volume percentage).
Arterial oxygen content is approximately 20 g/dL, the venous oxygen content is 15 g/dL. And dissolved oxygen contributes 0.1 g/dL in each case (but is continuously replenish from the hemoglobin-bound pool).
- The sigmoid shape of the oxy-Hb dissociation curve results from the allosteric interactions of the globin monomers that make up the hemoglobin tetramer as each one binds O2.
- Multiple factors can affect the affinity of Hb for oxygen. Thus causing the curve to shift to the left (increased oxygen affinity) or the right (decreased O2 affinity)
The oxygen-hemoglobin dissociation curve correlates with the oxygen saturation of hemoglobin across a range of oxygen pressures. The solid black line shows the curve for normal adult hemoglobin (Hb A). Notable points on the curve include:
- p50 — The p50 is the pressure at which hemoglobin is 50% saturated (27 mmHg on the X-axis).
- Arterial blood — Hemoglobin is approximately 100% saturated at an oxygen pressure of 100 mmHg.
- Venous blood — Hemoglobin is approximately 75% saturated.
Conditions that shift the curve may affect oxygen delivery to the tissues. These effects are most pronounced at low partial pressures of oxygen:
- Left shift — Conditions that shift the curve to the left (dashed red line) increase the oxygen affinity; hemoglobin holds more tightly onto oxygen and delivers less oxygen to the tissues at a given arterial oxygen pressure. The left-shifted curve for Hb F allows oxygen transfer from the maternal to the fetal circulation.
- Right shift — Conditions that shift the curve to the right (dashed blue line) decrease oxygen affinity; hemoglobin holds less tightly onto oxygen and delivers more oxygen to the tissues at a given arterial oxygen pressure.