| ultrasonography, doppler, colour | Ultrasonography applying the doppler effect, with the superposition of flow information as colours on a gray scale in a real-time image. This type of ultrasonography is well-suited to identifying the location of high-velocity flow (such as in a stenosis) or of mapping the extent of flow in a certain region. (12 Dec 1998) |
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| ultrasonography, doppler, duplex | Ultrasonography applying the doppler effect combined with real-time imaging. The real-time image is created by rapid movement of the ultrasound beam. A powerful advantage of this technique is the ability to estimate the velocity of flow from the doppler shift frequency. (12 Dec 1998) |
| ultrasonography, doppler, pulsed | Ultrasonography applying the doppler effect, with velocity detection combined with range discrimination. Short bursts of ultrasound are transmitted at regular intervals and the echoes are demodulated as they return. (12 Dec 1998) |
| ultrasonography, doppler, transcranial | A non-invasive technique using ultrasound for the measurement of cerebrovascular haemodynamics, particularly cerebral blood flow velocity and cerebral collateral flow. With a high-intensity, low-frequency pulse probe, the intracranial arteries may be studied transtemporally, transorbitally, or from below the foramen magnum. (12 Dec 1998) |
| foetal doppler study | <radiology> Non-stress test (NST), external monitoring for 20 minutes; poor specificity, greater than4 foetal heart accelerations (greater than15 bpm over baseline for 15 seconds) following foetal movement in foetus greater than34 weeks, no heart accelerations in immaturity, sleep, maternal sedation contraction stress test (CST), external monitoring after oxytocin or maternal breast stimulation, greater than 3 uterine contraction in 10 minutes; 50% specificity uterine and umbilical artery waveform, elevated systolic:diastolic ratio = increased vascular resistance foetal aortic flow volume, 185-246 ml/kg/min see also: biophysical profile, intrauterine growth retardation (IUGR) (12 Dec 1998) |
| laser-doppler flowmetry | A method of non-invasive, continuous measurement of microcirculation. The technique is based on the values of the doppler effect of low-power laser light scattered randomly by static structures and moving tissue particulates. (12 Dec 1998) |
| active principle | A constituent of a drug, usually an alkaloid or glycoside, upon the presence of which the characteristic therapeutic action of the substance largely depends. (05 Mar 2000) |
| antianaemic principle | The material in liver (and certain other tissues) that stimulates haemopoiesis in pernicious anaemia; for practical purposes, the antianaemic effect of extracts from such tissues is approximately equivalent to the content of vitamin B12. (05 Mar 2000) |
| azygos vein principle | A principle based on the observation that animals can survive prolonged vena caval occlusion without sequelae: if blood from the azygos vein alone is permitted to enter the heart, patients are perfused during cardiac and pulmonary bypass at flows much less than the normal resting cardiac output. Synonym: low flow principle. (05 Mar 2000) |
| Bernoulli's principle | <physics> When friction is negligible, the velocity of flow of a gas or fluid through a tube is inversely related to its pressure against the side of the tube; i.e., velocity is greatest and pressure lowest at a point of constriction. Synonym: Bernoulli's principle, Bernoulli's theorem. (05 Mar 2000) |
| pain-pleasure principle | A psychoanalytic concept that, in a human's psychic functioning, he/she tends to seek pleasure and avoid pain; a term borrowed by experimental psychology to denote the same tendency of an animal in a learning situation. Synonym: pleasure principle. (05 Mar 2000) |
| reality principle | The concept that the pleasure principle in personality development is modified by the demands of external reality; the principle or force that compels the growing child to adapt to the demands of external reality. (05 Mar 2000) |
| Pauli's exclusion principle | The theory limiting the number of electrons in the orbit or shell of an atom; that it is not possible for any two electrons to have all four quantum numbers identical. (05 Mar 2000) |
| repetition-compulsion principle | In psychoanalysis, the impulse to redramatise or reenact earlier emotional experiences or situations. Synonym: principle of inertia. (05 Mar 2000) |
| melanophore-expanding principle | A polypeptide hormone secreted by the intermediate lobe of the hypophysis in humans (in neurohypophysis in certain other species) which causes dispersion of melanin by melanophores, resulting in darkening of the skin, presumably by promoting melanin synthesis; this effect is readily demonstated in some lower vertebrates, such as frogs and fish; alpha-melanotropin is an N-acetylated peptide with 13 amino acids; beta-melanotropin has 22 amino acids. Synonym: intermedin, melanocyte-stimulating hormone, melanophore-expanding principle. (05 Mar 2000) |