Perfusion

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A Lindbergh perfusion pump, c. 1935, an early device for simulating natural perfusion Lindbergh perfusion pump in Putnam Gallery, 2009-11-24.jpg
A Lindbergh perfusion pump, c. 1935, an early device for simulating natural perfusion

Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, [1] usually referring to the delivery of blood to a capillary bed in tissue. Perfusion may also refer to fixation via perfusion, used in histological studies. Perfusion is measured as the rate at which blood is delivered to tissue, [2] or volume of blood per unit time (blood flow) per unit tissue mass. The SI unit is m3/(s·kg)[ citation needed ], although for human organs perfusion is typically reported in ml/min/g. [3] The word is derived from the French verb perfuser, meaning to "pour over or through". [4] All animal tissues require an adequate blood supply for health and life. Poor perfusion (malperfusion), that is, ischemia, causes health problems, as seen in cardiovascular disease, including coronary artery disease, cerebrovascular disease, peripheral artery disease, and many other conditions.

Contents

Tests verifying that adequate perfusion exists are a part of a patient's assessment process that are performed by medical or emergency personnel. The most common methods include evaluating a body's skin color, temperature, condition (dry/soft/firm/swollen/sunken/etc), and capillary refill.

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, August Krogh was awarded the Nobel Prize in Physiology or Medicine for his discovering the mechanism of regulation of capillaries in skeletal muscle. [6] [7] Krogh was the first to describe the adaptation of blood perfusion in muscle and other organs according to demands through the opening and closing of arterioles and capillaries.[ citation needed ]

Malperfusion

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 ]

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 radioactive isotopes have been widely used to measure perfusion since the 1960s. Radioactively labeled particles are injected into the test subject and a radiation detector measures radioactivity in tissues of interest. [8] Microspheres are used in radionuclide angiography, a method of diagnosing heart problems.

In the 1990s, methods for using fluorescent microspheres became a common substitute for radioactive particles. [9]

Nuclear medicine

Perfusion of various tissues can be readily measured in vivo with nuclear medicine methods which are mainly positron emission tomography (PET) and single photon emission computed tomography (SPECT).[ citation needed ] Various radiopharmaceuticals targeted at specific organs are also available, some of the most common are:[ citation needed ]

Magnetic resonance imaging

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

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 thermal diffusion and then separating it into thermal conductivity and perfusion components. [13] rCBF is usually measured continuously in time. It is necessary to stop the measurement periodically to cool down and reassess the thermal conductivity.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Single-photon emission computed tomography</span> Nuclear medicine tomographic imaging technique

Single-photon emission computed tomography is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera, but is able to provide true 3D information. This information is typically presented as cross-sectional slices through the patient, but can be freely reformatted or manipulated as required.

<span class="mw-page-title-main">Nuclear medicine</span> Medical specialty

Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emitted from within the body rather than radiation that is transmitted through the body from external sources like X-ray generators. In addition, nuclear medicine scans differ from radiology, as the emphasis is not on imaging anatomy, but on the function. For such reason, it is called a physiological imaging modality. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine.

<span class="mw-page-title-main">Cerebral circulation</span> Brain blood supply

Cerebral circulation is the movement of blood through a network of cerebral arteries and veins supplying the brain. The rate of cerebral blood flow in an adult human is typically 750 milliliters per minute, or about 15% of cardiac output. Arteries deliver oxygenated blood, glucose and other nutrients to the brain. Veins carry "used or spent" blood back to the heart, to remove carbon dioxide, lactic acid, and other metabolic products. The neurovascular unit regulates cerebral blood flow so that activated neurons can be supplied with energy in the right amount and at the right time. Because the brain would quickly suffer damage from any stoppage in blood supply, the cerebral circulatory system has safeguards including autoregulation of the blood vessels. The failure of these safeguards may result in a stroke. The volume of blood in circulation is called the cerebral blood flow. Sudden intense accelerations change the gravitational forces perceived by bodies and can severely impair cerebral circulation and normal functions to the point of becoming serious life-threatening conditions.

<span class="mw-page-title-main">Neuroimaging</span> Set of techniques to measure and visualize aspects of the nervous system

Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Increasingly it is also being used for quantitative research studies of brain disease and psychiatric illness. Neuroimaging is highly multidisciplinary involving neuroscience, computer science, psychology and statistics, and is not a medical specialty. Neuroimaging is sometimes confused with neuroradiology.

Functional imaging is a medical imaging technique of detecting or measuring changes in metabolism, blood flow, regional chemical composition, and absorption.

<span class="mw-page-title-main">Myocardial perfusion imaging</span> Nuclear medicine imaging method

Myocardial perfusion imaging or scanning is a nuclear medicine procedure that illustrates the function of the heart muscle (myocardium).

Kenneth Kin Man Kwong is a Hong Kong-born American nuclear physicist. He is a pioneer in human brain imaging. He received his bachelor's degree in Political Science in 1972 from the University of California, Berkeley. He went on to receive his Ph.D. in physics from the University of California, Riverside studying photon-photon collision interactions.

Perfusion is the passage of fluid through the lymphatic system or blood vessels to an organ or a tissue. The practice of perfusion scanning is the process by which this perfusion can be observed, recorded and quantified. The term perfusion scanning encompasses a wide range of medical imaging modalities.

Rubidium-82 (82Rb) is a radioactive isotope of rubidium. 82Rb is widely used in myocardial perfusion imaging. This isotope undergoes rapid uptake by myocardiocytes, which makes it a valuable tool for identifying myocardial ischemia in Positron Emission Tomography (PET) imaging. 82Rb is used in the pharmaceutical industry and is marketed as Rubidium-82 chloride under the trade names RUBY-FILL and CardioGen-82.

Preclinical imaging is the visualization of living animals for research purposes, such as drug development. Imaging modalities have long been crucial to the researcher in observing changes, either at the organ, tissue, cell, or molecular level, in animals responding to physiological or environmental changes. Imaging modalities that are non-invasive and in vivo have become especially important to study animal models longitudinally. Broadly speaking, these imaging systems can be categorized into primarily morphological/anatomical and primarily molecular imaging techniques. Techniques such as high-frequency micro-ultrasound, magnetic resonance imaging (MRI) and computed tomography (CT) are usually used for anatomical imaging, while optical imaging, positron emission tomography (PET), and single photon emission computed tomography (SPECT) are usually used for molecular visualizations.

<span class="mw-page-title-main">Cardiac magnetic resonance imaging perfusion</span>

Cardiac magnetic resonance imaging perfusion, also known as stress CMR perfusion, is a clinical magnetic resonance imaging test performed on patients with known or suspected coronary artery disease to determine if there are perfusion defects in the myocardium of the left ventricle that are caused by narrowing of one or more of the coronary arteries.

Cardiac imaging refers to minimally invasive imaging of the heart using ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), or nuclear medicine (NM) imaging with PET or SPECT. These cardiac techniques are otherwise referred to as echocardiography, Cardiac MRI, Cardiac CT, Cardiac PET and Cardiac SPECT including myocardial perfusion imaging.

Cerebral autoregulation is a process in mammals that aims to maintain adequate and stable cerebral blood flow. While most systems of the body show some degree of autoregulation, the brain is very sensitive to over- and underperfusion. Cerebral autoregulation plays an important role in maintaining an appropriate blood flow to that region. Brain perfusion is essential for life, since the brain has a high metabolic demand. By means of cerebral autoregulation, the body is able to deliver sufficient blood containing oxygen and nutrients to the brain tissue for this metabolic need, and remove CO2 and other waste products.

<span class="mw-page-title-main">Intravoxel incoherent motion</span> Concept and a method initially introduced and developed by Le Bihan et al

Intravoxel incoherent motion (IVIM) imaging is a concept and a method initially introduced and developed by Le Bihan et al. to quantitatively assess all the microscopic translational motions that could contribute to the signal acquired with diffusion MRI. In this model, biological tissue contains two distinct environments: molecular diffusion of water in the tissue, and microcirculation of blood in the capillary network (perfusion). The concept introduced by D. Le Bihan is that water flowing in capillaries mimics a random walk (Fig.1), as long as the assumption that all directions are represented in the capillaries is satisfied.

<span class="mw-page-title-main">Perfusion MRI</span>

Perfusion MRI or perfusion-weighted imaging (PWI) is perfusion scanning by the use of a particular MRI sequence. The acquired data are then post-processed to obtain perfusion maps with different parameters, such as BV, BF, MTT and TTP.

<span class="mw-page-title-main">MRI pulse sequence</span>

An MRI pulse sequence in magnetic resonance imaging (MRI) is a particular setting of pulse sequences and pulsed field gradients, resulting in a particular image appearance.

Arterial spin labeling (ASL), also known as arterial spin tagging, is a magnetic resonance imaging technique used to quantify cerebral blood perfusion by labelling blood water as it flows throughout the brain. ASL specifically refers to magnetic labeling of arterial blood below or in the imaging slab, without the need of gadolinium contrast. A number of ASL schemes are possible, the simplest being flow alternating inversion recovery (FAIR) which requires two acquisitions of identical parameters with the exception of the out-of-slice saturation; the difference in the two images is theoretically only from inflowing spins, and may be considered a 'perfusion map'. The ASL technique was developed by Alan P. Koretsky, Donald S. Williams, John A. Detre and John S. Leigh Jr in 1992.

Cerebral blood volume is the blood volume in a given amount of brain tissue.

<span class="mw-page-title-main">Oxygen-15 labelled water</span> Chemical compound

Oxygen-15 labelled water (also known as 15O-water, [O-15]-H2O, or H215O) is a radioactive variation of regular water, in which the oxygen atom has been replaced by oxygen-15 (15O), a positron-emitting isotope. 15O-water is used as a radioactive tracer for measuring and quantifying blood flow using positron emission tomography (PET) in the heart, brain and tumors.

Arterial input function (AIF), also known as a plasma input function, refers to the concentration of tracer in blood-plasma in an artery measured over time. The oldest record on PubMed shows that AIF was used by Harvey et al. in 1962 to measure the exchange of materials between red blood cells and blood plasma, and by other researchers in 1983 for positron emission tomography (PET) studies. Nowadays, kinetic analysis is performed in various medical imaging techniques, which requires an AIF as one of the inputs to the mathematical model, for example, in dynamic PET imaging, or perfusion CT, or dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

References

  1. ↑ American Psychological Association (APA): perfusion. (n.d.). Dictionary.com Unabridged (v 1.1). Retrieved March 20, 2008, from Dictionary.com website: http://dictionary.reference.com/browse/perfusion
  2. ↑ Thomas DL, Lythgoe MF, Pell GS, Calamante F, Ordidge RJ (2000). "The measurement of diffusion and perfusion in biological systems using magnetic resonance imaging". Phys Med Biol. 45 (8): R97-138. doi:10.1088/0031-9155/45/8/201. PMID   10958179.
  3. ↑ Engblom H, Xue H, Akil S, Carlsson M, Hindorf C, Oddstig J, Hedeer F, Hansen MS, Aletras AH, Kellman P, Arheden H (2017). "Fully quantitative cardiovascular magnetic resonance myocardial perfusion ready for clinical use: a comparison between cardiovascular magnetic resonance imaging and positron emission tomography". J Cardiovasc Magn Reson. 19 (1): 78. doi: 10.1186/s12968-017-0388-9 . PMC   5648469 . PMID   29047385.
  4. ↑ "Perfusion > What is Perfusion?". Cardiovascular Perfusion Forum.
  5. ↑ "Perfusion > Perfusion Services". Specialty Care Services Group. Archived from the original on 2018-12-17. Retrieved 2017-01-02.
  6. ↑ Larsen, E. H. (2007). "August Krogh (1874–1949): 1920 Nobel Prize". Ugeskrift for Laeger. 169 (35): 2878. PMID   17877986.
  7. ↑ Sulek, K. (1967). "Nobel prize for August Krogh in 1920 for his discovery of regulative mechanism in the capillaries". Wiadomosci Lekarskie. 20 (19): 1829. PMID   4870667.
  8. ↑ Studies of the Circulation with Radioactive Microspheres., Wagner et al, Invest. Radiol., 1969. 4(6): p. 374-386.
  9. ↑ "Fluorescent Microspheres" (PDF). Fluorescent Microsphere Resource Center. Archived from the original (PDF) on 2012-10-02.
  10. ↑ Huettel, S. A.; Song, A. W.; McCarthy, G. (2009), Functional Magnetic Resonance Imaging (2 ed.), Massachusetts: Sinauer, ISBN   978-0-87893-286-3
  11. ↑ Detre, John A.; Rao, Hengyi; Wang, Danny J. J.; Chen, Yu Fen; Wang, Ze (2012-05-01). "Applications of arterial spin labeled MRI in the brain". Journal of Magnetic Resonance Imaging. 35 (5): 1026–1037. doi:10.1002/jmri.23581. ISSN   1522-2586. PMC   3326188 . PMID   22246782.
  12. ↑ L. Axel. Cerebral blood flow determination by rapid-sequence computed-tomography: theoretical analysis. Radiology 137: 679–686, December 1980
  13. ↑ Vajkoczy P, Roth H, Horn P, et al. (August 2000). "Continuous monitoring of regional cerebral blood flow: experimental and clinical validation of a novel thermal diffusion microprobe". Journal of Neurosurgery. 93 (2): 265–74. doi:10.3171/jns.2000.93.2.0265. PMID   10930012. S2CID   30375395.
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