| HFO | high-frequency oscillator; high-frequency oscillatory [ventilation] |
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| HFT | high-frequency transduction; high-frequency transfer |
| HIHA | high impulsiveness, high anxiety |
| HPF | heparin-precipitable fraction; hepatic plasma flow; high-pass filter; high-power field [microscope];... |
| HRP | high-risk patient; high-risk pregnancy; histidine-rich protein; horseradish peroxidase |
| high energy bond | <chemistry> Chemical bonds that release more than 25kJ/mol on hydrolysis: their importance is that the energy can be used to transfer the hydrolysed residue to another compound. The risk in using the term is that students may think the bond itself is different in some way, whereas it is the compound that matters. Hydrolysis of creatine phosphate yields 42.7kJ/mol, of phosphoenolpyruvate, 53.2, ATP to ADP, 30.5: the latter is important because it shows that energetically the hydrolysis of creatine phosphate will suffice to reconstitute ATP, hence the use of creatine phosphate in muscle. (18 Nov 1997) |
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| high energy compounds | Classically, a group of phosphoric esters whose hydrolysis takes place with a standard free energy change of -5 to -15 kcal/mol (or, -20 to -63 kJ/mol) (in contrast to -1 to -4 kcal/mol or, -4 to -17 kJ/mol) for simple phosphoric esters like glucose-6-phosphate or alpha-glycerophosphates), thus being capable of driving energy-consuming reactions in living cells or reconstituted cell-free systems; adenosine 5'-triphosphate, with respect to the beta-and gamma-phosphates, is the best known and is regarded as the immediate energy source for most metabolic syntheses. The general types are acid anhydrides, phosphoric esters of enols, phosphamic acid (R-NH-PO3H2) derivatives, acyl thioesters (e.g., of coenzyme A), sulfonium compound's (R3-S+), and aminoacyl esters of ribosyl moieties. See: high energy phosphates. (05 Mar 2000) |
| high energy particle generating unit | A machine capable of providing highly energised radiation for the purposes of radiotherapy treatment. (16 Dec 1997) |
| high energy phosphate bond | See: high energy phosphates. (05 Mar 2000) |
| high energy phosphates | Those phosphate's that, on hydrolysis, yield an unusually large amount of energy; e.g., nucleotide polyphosphates such as ATP, enol phosphate's such as phosphoenolpyruvate. See: high energy compounds. Synonym: energy-rich phosphates. (05 Mar 2000) |
| high-energy shock waves | Compression waves of large amplitude, across which density, pressure, and particle velocity change drastically. (12 Dec 1998) |
| high extinction microscopy | <technique> Polarized-light, interference, fluorescence, and other modes of microscopy using polarization rectifiers and other devices to achieve a high degree of back- ground extinction in order to bring out the signal originating from a very small degree of birefringence, optical path difference, fluorescence etc. (05 Aug 1998) |
| high-fat diet | A diet containing large amounts of fat. (05 Mar 2000) |
| high-fibre diet | A diet high in the nondigestible part of plants, which is fibre. Fibre is found in fruits, vegetables, whole grains, and legumes. Insoluble fibre increases stool bulk, decreases transit time of food in the bowel, and decreases constipation and the risk of colon cancer. Soluble fibre delays absorption of glucose, which helps to control blood sugar in diabetes mellitus, and delays absorption of lipids, which helps to control hyperlipidemia. Recommended in treatment of diverticular disease of the colon. (05 Mar 2000) |
| high forceps delivery | Delivery by forceps applied to the foetal head before engagement has taken place. (05 Mar 2000) |
| high frequency current | An alternating electric current having a frequency of 10,000 or more per second; it produces no muscular contractions and does not affect the sensory nerves. Synonym: d'Arsonval current, Tesla current. (05 Mar 2000) |
| high frequency deafness | Selective loss of hearing acuity for high frequencies, usually associated with neurosensory damage; common in acoustic trauma. (05 Mar 2000) |
| high-frequency jet ventilation | Respiratory support system used primarily with rates of about 100 to 200/min with volumes of from about one to three times predicted anatomic dead space. Used to treat respiratory failure and maintain ventilation under severe circumstances. (12 Dec 1998) |
| high frequency recombination strain | A type of bacterial strain which is able to pass on genetic information to neighboring bacteria at a high rate. The high-frequency recombination strain (Hfr) is able to do this because it possesses the f plasmid and can therefore initiate bacterial conjugation. (09 Oct 1997) |
| high frequency transduction | Specialised transduction in which the donor bacterium contains not only the transducing, defective probacteriophage but also nondefective prophage that serves as "helper" virus, enabling most of the defective prophage particles to develop sufficiently to function as transducing agents. (05 Mar 2000) |