Effusion


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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 ?
Echocardiography and chest CT showing enlargement of lymph node with an inner low-density shadow and pericardial effusions could provide key clues for the diagnosis of mediastinal infection.
Hence, we carried out this study with an objective of highlighting the importance of pleural fluid ADA plus basic pleural fluid analysis in form of routine and microscopy examination in evaluating a case of tuberculous pleural effusion.
Objectives of the study was to compare the pleural fluid ADA level between tuberculous and non-tuberculous pleural effusion and to establish the diagnostic value of pleural fluid ADA level in tuberculous pleural effusion by using statistical methods.
White arrow shows ultrasonographic visualization of a pleural effusion between the visceral and parietal pleura
Serial chest X-rays showed that the effusion was progressively getting smaller and complete re-absorption was seen four months later.
Massive effusion was defined as the liquid volume occupying more than half of the hemithorax.
Pleural effusion is a commonly encountered pathology by any pulmonary physician.
1) When an effusion is only partially well-marginated on chest radiograph, this is known as the incomplete border sign.
Three months later, the patient had recurrent dyspnea and clinical signs of cardiac tamponade and a large pericardial effusion was found on echocardiography.
Bedside echocardiography is one of the gold standard investigations to diagnose pericardial effusion with cardiac tamponade.
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).