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Through a process called the haemodynamic response, blood releases oxygen to active neurons at a greater rate than to inactive neurons. This causes a change of the relative levels of oxyhemoglobin and deoxyhemoglobin (oxygenated or deoxygenated blood) that can be detected on the basis of their differential magnetic susceptibility.
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. This difference is used for the measurement of the amount of oxygen in a patient's blood by an instrument called a pulse oximeter.
In addition to the total concentration of hemoglobin, the oxygen saturation will define the concentration of oxy- and deoxyhemoglobin in tissue and so the total absorption spectrum. Depending on the type of tissue, we can consider different situations. Below, the total concentration of hemoglobin is assumed to be 2.3 mM.
The signal is often compared with the BOLD signal measured by fMRI and is capable of measuring changes both in oxy- and deoxyhemoglobin concentration, [2] but can only measure from regions near the cortical surface. fNIRS may also be referred to as Optical Topography (OT) and is sometimes referred to simply as NIRS.
This decrease in blood flow in the cerebral vascular system can result in a buildup of metabolic wastes generated by neurons and glial cells and a decrease in oxygen and glucose delivery to them. As a result, cellular energy failure, depolarization of neuronal and glial membranes, edema , and excess neurotransmitter and calcium ion release can ...
In the oxygen-rich capillaries of the lung, this property causes the displacement of carbon dioxide to plasma as low-oxygen blood enters the alveolus and is vital for alveolar gas exchange. The general equation for the Haldane Effect is: H + + HbO 2 ⇌ H + Hb + O 2; However, this equation is confusing as it reflects primarily the Bohr effect.
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This curve is an important tool for understanding how our blood carries and releases oxygen. Specifically, the oxyhemoglobin dissociation curve relates oxygen saturation (SO 2) and partial pressure of oxygen in the blood (PO 2), and is determined by what is called "hemoglobin affinity for oxygen"; that is, how readily hemoglobin acquires and ...