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In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. The word is derived from the French verb "perfuser" meaning to "pour over or through."
The term "Pa - Pv" is sometimes presented as "ΔP", for the change in pressure.
The terms "perfusion" and "perfusion pressure" are sometimes used interchangeably, but the equation should make clear that resistance can have an effect on the perfusion, but not on the perfusion pressure.
Overperfusion and underperfusionEdit
The terms "overperfusion" and "underperfusion" are measured relative to the average level of perfusion across all tissues in an individual body, and the terms should not be confused with hypoperfusion and "hyperperfusion", which measure the perfusion level to the tissue's current need.
Tissues like the skin are considered overperfused and receive more blood than would be expected to meet the metabolic needs of the tissue. In the case of the skin, extra blood flow is used for thermoregulation. In addition to delivering oxygen, the blood helps dissipate heat by redirecting warm blood close to the surface where it can cool the body through the sweating and thermal radiation.
Measurement using MRIEdit
- The first is based on the use of injected contrast agent that changes the magnetic susceptibility of blood and thereby the MR signal which is repeatedly measured during bolus passage.
- The other category is based on arterial spin labeling (ASL), where arterial blood is magnetically tagged before it enters into the tissue of interest and the amount of labeling is measured and compared to a control recording obtained without spin labeling.
Respiratory system, physiology: respiratory physiology
lung volumes - vital capacity - functional residual capacity - respiratory minute volume - closing capacity - dead space - spirometry - body plethysmography - peak flow meter - thoracic independent volume - bronchial challenge test
ventilation/perfusion ratio (V/Q) and scan - zones of the lung - gas exchange - pulmonary gas pressures - alveolar gas equation - hemoglobin - oxygen-haemoglobin dissociation curve (2,3-DPG, Bohr effect, Haldane effect) - carbonic anhydrase (chloride shift) - oxyhemoglobin - respiratory quotient - arterial blood gas - diffusion capacity - Dlco
|Control of respiration|
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