Perfusion

Perfusion is the passage of fluid through the

During major surgery, especially cardiothoracic surgery, perfusion must be maintained and managed by the health professionals involved, rather than left to the body's homeostasis alone. As the lead surgeons are often too busy to handle all hemodynamic control by themselves, specialists called perfusionists manage this aspect. There are more than one hundred thousand perfusion procedures annually.^[5]

Discovery

In 1920,

Malperfusion can refer to any type of incorrect perfusion though it usually refers to hypoperfusion. The meaning of the terms "overperfusion" and "underperfusion" is relative to the average level of perfusion that exists across all the tissues in an individual body. Perfusion levels also differ from person to person depending on metabolic demand.^[citation needed]

Examples follow:^{[citation needed]}

• Heart tissues are considered overperfused because they normally are receiving more blood than the rest of tissues in the organism; they need this blood because they are constantly working.
• In the case of skin cells, extra blood flow in them is used for
  thermal dissipation
  .
• Many types of
  tumors
  , and especially certain types, have been described as "hot and bloody" because of their overperfusion relative to the body overall.

Overperfusion and underperfusion should not be confused with hypoperfusion and hyperperfusion, which relate to the perfusion level relative to a tissue's current need to meet its metabolic needs. For example, hypoperfusion can be caused when an artery or arteriole that supplies blood to a volume of tissue becomes blocked by an embolus, causing either no blood or at least not enough blood to reach the tissue. Hyperperfusion can be caused by inflammation, producing hyperemia of a body part. Malperfusion, also called poor perfusion, is any type of incorrect perfusion. There is no official or formal dividing line between hypoperfusion and ischemia; sometimes the latter term refers to zero perfusion, but often it refers to any hypoperfusion that is bad enough to cause necrosis.^{[citation needed]}

Measurement

In equations, the symbol Q is sometimes used to represent perfusion when referring to cardiac output. However, this terminology can be a source of confusion since both cardiac output and the symbol Q refer to flow (volume per unit time, for example, L/min), whereas perfusion is measured as flow per unit tissue mass (mL/(min·g)).^{[citation needed]}

Microspheres

Microspheres that are labeled with

Perfusion of various tissues can be readily measured

• rCBF
  ) studied with SPECT
• Tetrofosmin and Sestamibi for myocardial perfusion imaging
  with SPECT
• rCBF
  ) with SPECT
• rCBF
  ) with PET (absolute quantification is possible when measuring arterial radioactivity concentration)
• ⁸²Rb-chloride for measuring myocardial perfusion with PET (absolute quantification is possible)

Magnetic resonance imaging

Two main categories of magnetic resonance imaging (MRI) techniques can be used to measure tissue perfusion in vivo.

• The first is based on the use of an injected contrast agent that changes the magnetic susceptibility of blood and thereby the MR signal which is repeatedly measured during bolus passage.^[10]
• The other category is based on arterial spin labelling (ASL), where arterial blood is magnetically tagged before it enters into the tissue being examined and the amount of labelling that is measured and compared to a control recording obtained without spin labelling.^[11]

Computed tomography (CT)

Brain perfusion (more correctly transit times) can be estimated with contrast-enhanced computed tomography.^[12]

Thermal diffusion

Perfusion can be determined by measuring the total

• Reperfusion injury – Tissue damage after return of blood supply following ischemia or hypoxia
• Machine perfusion
• Perfusionist – Healthcare professional who uses the cardiopulmonary bypass machine
• Myocardial perfusion imaging – Nuclear medicine imaging method
• rCBF – Brain blood supply
• Cerebral edema – Excess accumulation of fluid (edema) in the intracellular or extracellular spaces of the brain
• Pressure ulcer — continuous external pressure impairs perfusion

References