The transfer of ?uid through a tissue. For example, when blood passes through the lung tissue, dissolved oxygen perfuses from the moist air in the alveoli to the blood. Fluid may also be deliberately introduced into a tissue by injecting it into the blood vessels supplying the tissue. It is used as a sign of how adequate the circulation is at the time of illness. Poor peripheral perfusion, a sign of circulatory collapse or shock, is recognised by pressing on the skin to force blood from capillaries. The time it takes for them to re?ll and the skin to become pink is noted: more than 5 seconds, and the circulation is likely to be compromised.
n. 1. the passage of fluid through a tissue, especially the passage of blood through the lung tissue to pick up oxygen from the air in the alveoli, which is brought there by *ventilation, and release carbon dioxide. If ventilation is impaired deoxygenated venous blood is returned to the general circulation. If perfusion is impaired insufficient gas exchange takes place. 2. the deliberate introduction of fluid into a tissue, usually by injection into the blood vessels supplying the tissue.
a technique for demonstrating an abnormal blood supply to an organ by injecting a radioactive *tracer or *contrast medium. One of the most common uses, often in conjunction with ventilation scanning (see ventilation-perfusion scanning), is to detect obstruction of pulmonary arteries due to embolism by thrombus (see pulmonary embolism). Particles labelled with radioactive tracer are injected intravenously and become temporarily lodged in the capillaries in the lungs. Areas not being perfused show up as holes on the gamma-camera images. In *magnetic resonance imaging or *computerized tomography, contrast medium is injected and a series of images is obtained. The rate of change of enhancement is an index of the blood supply to the area of interest. This technique can be used to study blood supply to the brain, heart, or kidneys (in particular), to help diagnose arterial strictures or blockages, or tumours in which blood supply may be increased by abnormal vessels.... perfusion scan
(V/Q scanning) a nuclear medicine technique in which two different isotopes are used, one inhaled (usually *xenon-133 or *krypton-81m), to examine lung ventilation, and the other injected into a vein, to examine lung perfusion. In *pulmonary embolism, the area of lung supplied by the blocked artery is not being perfused with blood – which gives a perfusion defect on the film – but has normal ventilation. This technique is highly sensitive for pulmonary embolism.... ventilation-perfusion scanning
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