Effusion


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Related to Effusion: pleural effusion, Pericardial effusion

effusion

1. the flow of a gas through a small aperture under pressure, esp when the density is such that the mean distance between molecules is large compared to the diameter of the aperture
2. Med
a. the escape of blood or other fluid into a body cavity or tissue
b. the fluid that has escaped

Effusion

 

the slow leakage of gas through a small aperture. Two cases of effusion are distinguished. In the first case, the diameter of the opening is small compared with the mean free path of the molecules (the pressure in the vessel is very low). In such a case, molecular effusion occurs in which collisions between molecules play no part, and the overall volume of gas escaping per unit time is Effusion, where S is the area of the aperture, μ is the molecular mass of the gas, R is the universal gas constant, T is the absolute temperature of the gas, and p1 and p2 are the gas pressures on the two sides of the aperture. The effusion method of measuring very low pressures (about 10–3–10–4 mm Hg) is based on this case.

In the second case, where the gas pressure is so high that the mean free path is smaller than the diameter of the aperture, the leakage of gas obeys the laws of hydrodynamics. The molecules escape from the aperture in the form of a jet, and the volume of gas discharged per unit time is inversely proportional to the square root of the density of the gas. This law underlies a method of determining the density of gases from the time of their discharge through small apertures (0.10–0.01 mm). However, if the pressure within the vessel is considerably greater than the external pressure, the amount of gas escaping is proportional to the pressure in the vessel.


Effusion

 

the process of lava (magma) pouring out onto the earth’s surface. When the lava cools, effusive rocks are formed, bedded in the form of lava flows and lava sheets. Effusion, one of the manifestations of volcanic activity, is usually accompanied by an explosion, with discharges of small fragments (volcanic ash, sand, or tuff) or large chunks (volcanic bombs and slags). Viscous acidic lava sometimes will not flow, but rather is extended, forming volcanic domes.

effusion

[e′fyü·zhən]
(medicine)
A pouring out of any fluid into a body cavity or tissue.
(physical chemistry)
The movement of a gas through an opening which is small as compared with the average distance which the gas molecules travel between collisions.
(science and technology)
The act or process of leaking or pouring out.
Any material that is effused.
References in periodicals archive ?
In areas where Lyme disease is common, physicians should always consider whether a spontaneous knee effusion might be caused by the disease and test accordingly.
A pericardial effusion is a notable finding that is seen uncommonly in hypothyroidism but more frequently in patients with more severe thyroid hormone deficiency, such as in myxedema (4).
of autoinflation in 4- to 11-year-old school children with otitis media with effusion in primary care.
Based on the history and audiology alone, it appeared to be simply a middle ear effusion.
In review of the literature, autoimmunity associated with underlying connective tissue disease (CTD) and ILD has been postulated as an important cause of pleural effusion in PM-DM, given the similar histological patterns and early-onset of ILD in both PM-DM and rheumatoid arthritis (RA).
A portion of the coelomic effusion (14 mL) was removed via ultrasound-guided fine needle aspiration; it was clear with a green-brown coloration.
PDS, synovial thickening, and effusion were "persistent"--present at baseline and follow-up--in 40, 118, and 232 joints, and were "fluctuating" --present only at baseline or follow-up--in 243, 641, and 636 joints, respectively.
TPE-II: The decision by a clinician to treat a patient with a full course of TB chemotherapy, based on strong clinical and radiological evidence, in the absence of other causes of pleural effusion.
The Institute for Transuranium Elements plans the purchase of a nuclearised E+B Knudsen effusion mass spectrometer (KEMS) with glovebox.
2), (6) In the case of a bilateral effusion the spectrum of differential diagnoses is narrower than that of a unilateral effusion.
The limited availability of diagnostic testing in many settings to investigate unresolving pleural effusion despite TB treatment often presents a diagnostic dilemma.