| LCBF | local cerebral blood flow |
|---|---|
| LCGU | local cerebral glucose utilization |
| LERG | local electroretinogram |
| LES | Lambert-Eaton syndrome; Lawrence Experimental Station [agar]; local excitatory state; Locke egg seru... |
| LHC | Langerhans cell histiocytosis; left heart catheterization; left hypochondrium; light-harvesting comp... |
| hyperbaric oxygen | High pressure oxygen, oxygen at a pressure greater than 1 atmosphere. See: hyperbaric oxygenation. Singlet oxygen, an excited or higher energy form of oxygen characterised by the spin of a pair of electrons in opposite directions, whereas electron spin is unidirectional in normal molecular oxygen Because of its great reactivity, singlet oxygen is a probable intermediate in most photo-oxidation reactions. Although it exists for no more than 0.1 sec, it may react with atmospheric pollutants to foster smog formation and may have harmful biological effects. Triplet oxygen, the normal unexcited state of O2 in the atmosphere, in which the unpaired pair of electrons are so displaced that their magnetic fields are oriented in the same direction, resulting in paramagnetism; each of the heat-generated spectral lines of such oxygen can be split by a magnetic field into a triplet. Compare: singlet oxygen. (05 Mar 2000) |
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| hyperbaric oxygen therapy | <physiology> A pressurised chamber that allows for the delivery of oxygen in higher concentrations for therapeutic benefit. Useful in the treatment of severe burns, peripheral vascular disease, carbon monoxide poisoning and decompression illness. (04 Mar 1998) |
| singlet oxygen | An energised but uncharged form of oxygen that is produced in the metabolic burst of leucocytes and that can be toxic to cells. (18 Nov 1997) |
| dissolved oxygen | <biochemistry> The concentration of oxygen dissolved in water, expressed in mg/l or as percent saturation, where saturation is the maximum amount of oxygen that can theoretically be dissolved in water at a given altitude and temperature. (11 Jan 1998) |
| oxygen | 1. <chemistry> A colourless, tasteless, odorless, gaseous element occurring in the free state in the atmosphere, of which it forms about 23 per cent by weight and about 21 per cent by volume, being slightly heavier than nitrogen. Symbol O. Atomic weight 15.96. It occurs combined in immense quantities, forming eight ninths by weight of water, and probably one half by weight of the entire solid crust of the globe, being an ingredient of silica, the silicates, sulphates, carbonates, nitrates, etc. Oxygen combines with all elements (except fluorine), forming oxides, bases, oxyacid anhydrides, etc, the process in general being called oxidation, of which combustion is only an intense modification. at ordinary temperatures with most substances it is moderately active, but at higher temperatures it is one of the most violent and powerful chemical agents known. It is indispensable in respiration, and in general is the most universally active and efficient element. It may be prepared in the pure state by heating potassium chlorate. This element (called dephlogisticated air by Priestley) was named oxygen by Lavoisier because he supposed it to be a constituent of all acids. This is not so in the case of a very few acids (as hydrochloric, hydrobromic, hydric sulphide, etc), but these do contain elements analogous to oxygen in property and action. Moreover, the fact that most elements approach the nearer to acid qualities in proportion as they are combined with more oxygen, shows the great accuracy and breadth of Lavoisier's conception of its nature. Pharmacologic action: Increases the supply of oxygen to ischemic tissues. It is the most effective agent in emergency cardiac care. Uses: Always administer oxygen during emergency cardiac care. Dose: Nasal cannula with oxygen flow of 4 liters per minute provides FiO2 of about 30%. Nasal cannula with oxygen flow of 6-8 liters per minute provides FiO2 of 35-40%. Venturi mask can provide higher and more precise oxygen concentrations. Potential complications: Ensure that oxygen is being delivered. Carefully check all connections. Oxygen toxicity develops only after several days of exposure to high FiO2. Increased FiO2 may cause hypoventilation in COPD patients dependent on hypoxic ventilatory drive. This is very rare and simply requires starting at lower FiO2, careful observation, and assisted ventilation if necessary. Origin: F. Oxygene, from Gr. Sharp, acid + root of to be born. So called because originally supposed to be an essential part of every acid. (17 Mar 2000) |
| oxygen-15 | A cyclotron-produced, positron-emitting radioisotope of oxygen with a half-life of 122.2 seconds; used in studies of respiratory function and in positron emission tomography. (05 Mar 2000) |
| oxygen-16 | The common oxygen isotope, making up 99.76% of natural oxygen. (05 Mar 2000) |
| oxygen-17 | The rarest of the stable oxygen isotopes, making up 0.04% of natural oxygen. (05 Mar 2000) |
| oxygen-18 | A stable oxygen isotope making up 0.20% of natural oxygen; used in mass spectrometry and in NMR studies of tissue. Synonym: heavy oxygen. (05 Mar 2000) |
| oxygen affinity anoxia | Anoxia due to inability of haemoglobin to release oxygen. (05 Mar 2000) |
| oxygen affinity hypoxia | Hypoxia due to reduced ability of haemoglobin to release oxygen. (05 Mar 2000) |
| oxygen capacity | The maximum quantity of oxygen that will combine chemically with the haemoglobin in a unit volume of blood; normally it amounts to 1.34 ml of O2 per gm of Hb or 20 ml of O2 per 100 ml of blood. (05 Mar 2000) |
| oxygen compounds | Inorganic compounds that contain oxygen as an integral part of the molecule. (12 Dec 1998) |
| oxygen consumption | The rate at which oxygen is used by a tissue; microliters of oxygen stpd used per milligram of tissue per hour; the rate at which oxygen enters the blood from alveolar gas, equal in the steady state to the consumption of oxygen by tissue metabolism throughout the body. (12 Dec 1998) |
| oxygen debt | The extra oxygen (compared with its usual oxygen intake at rest) an organismconsumes after a period of strenouousphysical activity. (09 Oct 1997) |