Carbon Monoxide: Hemoglobin binds carbon monoxide (CO) 200 to 300 times more than with oxygen, resulting in the formation of carboxyhemoglobin and preventing the binding of oxygen to hemoglobin due to the competition of the same binding sites.

Pulse oximetry is a way to measure how much oxygen your blood is carrying. The blood oxygen level measured with an oximeter is called your oxygen saturation level (abbreviated O2sat or SaO2). This is a percentage of how much oxygen your blood is carrying compared to the maximum it is capable of carrying.

Oxygen is carried in the blood in two forms: (1) dissolved in plasma and RBC water (about 2% of the total) and (2) reversibly bound to hemoglobin (about 98% of the total).

Carbon monoxide has a greater affinity for hemoglobin than does oxygen. Therefore, when carbon monoxide is present, it binds to hemoglobin preferentially over oxygen. As a result, oxygen cannot bind to hemoglobin, so very little oxygen is transported throughout the body.

four molecules

Myoglobin is a small oxygen-binding protein found in muscle cells. This allows the oxygen that is binded to have a negative charge, which stabilizes it. Myoglobin’s affinity for oxygen is higher than hemoglobin. And unlike hemoglobin which is found in the red blood cells, myoglobin is found in muscle tissues.

Fetal hemoglobin has a higher oxygen-binding affinity than that of maternal hemoglobin. Fetal red blood cells have a higher affinity for oxygen than maternal red blood cells because fetal hemoglobin doesn’t bind 2,3-BPG as well as maternal hemoglobin does.

The shift of the oxygen dissociation curve to the right occurs in response to an increase in the partial pressure of carbon dioxide (Pco2), a decrease in pH, or both, the last of which is known as the Bohr effect.

Decreased carbon dioxide partial pressure will increase the affinity for oxygen rather than decrease it. Increased temperature and increased 2,3-bisphosphoglycerate will also decrease the hemoglobin affinity for oxygen.

The ‘double Bohr’ effect helps to increase fetal oxygenation. The transfer of carbon dioxide from fetal to maternal blood shifts the maternal oxyhaemoglobin curve to the right and the fetal curve to the left, facilitating the transfer of oxygen across the placenta from mother to fetus.

The Bohr effect is the shift to the right of the oxygen equilibrium curve of both adult and fetal blood in response to an increase in PCO2 or a decrease in pH, or both.

Haldane effect is what happens to pH and CO2 binding because of oxygen, and Bohr effect is what happens to oxygen binding because of CO2 and lower pH.

The Bohr effect describes hemoglobin’s lower affinity for oxygen secondary to increases in the partial pressure of carbon dioxide and/or decreased blood pH. This lower affinity, in turn, enhances the unloading of oxygen into tissues to meet the oxygen demand of the tissue.[1]

The Bohr effect is a phenomenon first described in 1904 by the Danish physiologist Christian Bohr. That is, the Bohr effect refers to the shift in the oxygen dissociation curve caused by changes in the concentration of carbon dioxide or the pH of the environment.

The Haldane effect is a property of hemoglobin first described by John Scott Haldane, within which oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin, increasing the removal of carbon dioxide. Consequently, oxygenated blood has a reduced affinity for carbon dioxide.

The Haldane Effect describes the effect of oxygen on CO2 transport. The Haldane Effect (along with the Bohr Effect) facilitates the release of O2 at the tissues and the uptake of O2 at the lungs.

As a buffer, hemoglobin counteracts any rise in blood pH by releasing H+ ions from a number of atomic sites throughout the molecule. Similarly, a number of H+ ions are bound to, or are ‘taken up’ by the molecule, acting to counteract a decrease in pH.

Carbon Monoxide The binding of one CO molecule to hemoglobin increases the affinity of the other binding spots for oxygen, leading to a left shift in the dissociation curve. This shift prevents oxygen unloading in peripheral tissue and therefore the oxygen concentration of the tissue is much lower than normal.

p50 is the oxygen tension when hemoglobin is 50 % saturated with oxygen. When hemoglobin-oxygen affinity increases, the oxyhemoglobin dissociation curve shifts to the left and decreases p50. When hemoglobin-oxygen affinity decreases, the oxyhemoglobin dissociation curve shifts to the right and increases p50 (Figure 1).

In contrast, an elevated (= alkaline or basic) blood plasma pH of 7.6 causes the O2-Hb saturation curve to shift about 15% to the left of normal. As blood plasma pH decreases (= becomes more acidic), H+ ions increasingly bind to hemoglobin amino acids, which lessens hemoglobin’s affinity for O2.

The oxygen–hemoglobin dissociation curve can be displaced such that the affinity for oxygen is altered. Factors that shift the curve include changes in carbon dioxide concentration, blood temperature, blood pH, and the concentration of 2,3-diphosphoglycerate (2,3-DPG).

It is easier to bind a second and third oxygen molecule to Hb than the first molecule. This is because the hemoglobin molecule changes its shape, or conformation, as oxygen binds. The fourth oxygen is then more difficult to bind.

Hemoglobin’s oxygen-binding curve forms in the shape of a sigmoidal curve. This is due to the cooperativity of the hemoglobin. Both these changes causes the hemoglobin to lose its affinity for oxygen, therefore making it drop the oxygen into the tissues.

THE CLASSICAL OXYGEN DISSOCIATION CURVE OF HEMOGLOBIN The shape of the oxygen dissociation curve of Hb is sigmoidal, whereas that of other oxygen-carrying molecules (such as Myoglobin) is hyperbolic.