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Deoxygenated hemoglobin (deoxyhemoglobin) is the form of hemoglobin without the bound oxygen. The absorption spectra of oxyhemoglobin and deoxyhemoglobin differ. The oxyhemoglobin has significantly lower absorption of the 660 nm wavelength than deoxyhemoglobin, while at 940 nm its absorption is slightly higher.
In 1990, three papers published by Seiji Ogawa and colleagues showed that hemoglobin has different magnetic properties in its oxygenated and deoxygenated forms (deoxygenated hemoglobin is paramagnetic and oxygenated hemoglobin is diamagnetic), both of which could be detected using MRI. [2]
Oxygenated and deoxygenated hemoglobin differ in absorption of light of different wavelengths. The oximeter uses light-emitting diodes of different wavelengths in conjunction with a light-sensitive sensor to measure the absorption of red and infrared wavelengths in the extremity, and estimates the SpO 2 from the absorption spectrum.
Histidine residues in hemoglobin can accept protons and act as buffers.Deoxygenated hemoglobin is a better proton acceptor than the oxygenated form. [1]In red blood cells, the enzyme carbonic anhydrase catalyzes the conversion of dissolved carbon dioxide to carbonic acid, which rapidly dissociates to bicarbonate and a free proton:
Deoxygenated blood is a darker shade of red; this is present in veins, and can be seen during blood donation and when venous blood samples are taken. This is because the spectrum of light absorbed by hemoglobin differs between the oxygenated and deoxygenated states. [35]
The color of human blood ranges from bright red when oxygenated to a darker red when deoxygenated. [2] It owes its color to hemoglobin, to which oxygen binds. Deoxygenated blood is darker due to the difference in shape of the red blood cell when oxygen binds to haemoglobin in the blood cell (oxygenated) versus does not bind to it (deoxygenated).
In adult hemoglobin, the binding of 2,3-bisphosphoglycerate (2,3-BPG) primarily occurs with the beta chains, preventing the binding of oxygen with haemoglobin. This binding is crucial for stabilizing the deoxygenated state of hemoglobin, promoting the efficient release of oxygen to body tissues.
In short, deoxygenated hemoglobin is paramagnetic while oxygenated hemoglobin is diamagnetic. Diamagnetic blood ( oxyhemoglobin ) interferes with the magnetic resonance (MR) signal less and this leads to an improved MR signal in that area of increased neuronal activity.