| systolic gradient | The difference in pressure during systole between two communicating cardiovascular chambers, e.g., between the left ventricle and aorta in aortic stenosis. (05 Mar 2000) |
|---|---|
| electrochemical gradient | A measure of the tendency of an ion to move passively from one point to another, taking into consideration the differences in its concentration and in the electrical potentials between the two points; commonly expressed as the additional voltage needed to achieve equilibrium. (05 Mar 2000) |
| ficoll gradient | A density gradient of ficoll (synthetic sucrose polymer) in solution, where concentration of the ficoll varies continuously through the solution. It is often used to separate different types of cells from each other during the process of sedimentation. (09 Oct 1997) |
| field gradient | In magnetic resonance imaging, a magnetic field that varies with location, superimposed on the uniform field of the magnet, to alter the resonant frequency of nuclei and allow recovery of their spatial position. Synonym: field gradient. (05 Mar 2000) |
| critical | 1. Denoting or of the nature of a crisis. 2. Denoting a morbid condition in which death is possible. 3. In sufficient quantity as to constitute a turning point. (05 Mar 2000) |
| critical angle | The angle of incidence at which a ray of light, in passing between two media, changes from refraction to total reflection. Synonym: limiting angle. (05 Mar 2000) |
| critical care | Health care provided to a critically ill patient during a medical emergency or crisis. (12 Dec 1998) |
| critical care unit | A hospital facility for provision of intensive nursing and medical care of critically ill patients, characterised by high quality and quantity of continuous nursing and medical supervision and by use of sophisticated monitoring and resuscitative equipment; may be organised for the care of specific patient groups, e.g., neonatal or newborn ICU, neurological ICU, pulmonary ICU. Synonym: critical care unit. (05 Mar 2000) |
| critical concentration | <chemistry> The minimum concentration of units needed before a biological polymer will form. Examples of biopolymers are microtubules from tubulin units, polypeptides from amino acid units, polysaccharides from simple sugar units, etc. (09 Oct 1997) |
| critical dissolved oxygen concentration | <biology> The minimum concentration of oxygen in the water needed for the growth of a culture which has been submerged, where oxygen is the limiting factor to the growth of the culture. (09 Oct 1997) |
| critical flicker fusion frequency | The minimal number of flashes of light per second at which an intermittent light stimulus no longer stimulates a continuous visual sensation. (05 Mar 2000) |
| critical habitat | <ecology> Specific areas within the geographic area occupied by a species at the time it is listed in accordance with the Endangered Species act. Specific areas outside the geographical area occupied by a species at the time it is listed if there is a determination that such areas are essential for conservation of the species. (09 Oct 1997) |
| critical illness | A disease or state in which death is possible or imminent. (12 Dec 1998) |
| critical illness polyneuropathy | A diffuse axon loss sensorimotor polyneuropathy seen in severely ill patients, usually in the intensive care unit; most patients have been on multiple drugs, and cannot be weaned from ventilatory support; electrodiagnostic studies show evidence of an axon loss polyneuropathy, predominantly motor; of unknown aetiology. (05 Mar 2000) |
| critical mass | <chemistry, radiobiology> The minimum amount of mass of a combination of radioactive substances needed for the substances to generate and lose an exactly balanced number of neutrons to make a chain reaction which will keep going by itself. (09 Oct 1997) |