| block | An obstruction or stoppage. (18 Nov 1997) |
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| block anaesthesia | Regional anaesthesia in which local anaesthetic solution is injected about nerves to inhibit nerve transmission; includes spinal, epidural, nerve block, and field block anaesthesia, but not local or topical anaesthesia. Synonym: block anaesthesia. (05 Mar 2000) |
| block book | A book printed from engraved wooden blocks instead of movable types. Source: Websters Dictionary (01 Mar 1998) |
| block design test | A performance test using coloured blocks which the individual must use to match pictured designs; one of the subtests of the Wechsler intelligence scales. (05 Mar 2000) |
| block vertebra | <radiology> Congenital vertebral fusion, location: lumbar or cervical, height of the fused vertebral bodies equals the sum of heights of the involved bodies and intervertebral disc, waist at level of disc space see: cervical spine fusion (12 Dec 1998) |
| block vertebrae | Congenitally fused and hypoplastic vertebral bodies which, on radiographs, give the appearance of a more or less solid bony mass. See: Klippel-Feil syndrome. (05 Mar 2000) |
| block-out | Elimination of undercuts by filling such areas with a medium such as wax or wet pumice. (05 Mar 2000) |
| blockade | 1. Intravenous injection of large amounts of colloidal dyes or other substances whereby the reaction of the reticuloendothelial cells to other influences (e.g., by phagocytosis) is temporarily prevented. 2. Arrest of peripheral nerve conduction or transmission at autonomic synaptic junctions, autonomic receptor sites, or myoneural junctions by a drug. (05 Mar 2000) |
| blocked aerogastria | The retention of gas in the stomach due to spasm of the sphincteric region of the lower oesophagus which prevents belching. (05 Mar 2000) |
| blocked reading frame | A sequence of DNA that cannot be translated into a viable protein; usually due to the interruption by one or more termination codons. Synonym: closed reading frame. (05 Mar 2000) |
| blocked tear duct | A blocked nasolacrimal duct which normally carries tears from the eyes to the nose. Commonly seen in infants, but usually resolves spontaneously by age 2-3. In adults blockage can occur from chronic sinusitis or trauma. A gentle massage of the lacrimal gland 2-3 times a day for several months may reopen the tear duct. (27 Sep 1997) |
| blocker | 1. An instrument used to obstruct a passage. See: blocking agent. (05 Mar 2000) |
| blocking | 1. Obstructing; arresting of passage, conduction, or transmission. 2. In psychoanalysis, a sudden break in free association occurring when a painful subject or repressed complex is touched. 3. Sudden cessation of thoughts and speech, which may indicate the presence of a severe thought disorder or a psychosis. (05 Mar 2000) |
| blocking activity | The repression or elimination of electrical activity in the brain by the arrival of a sensory stimulus. (05 Mar 2000) |
| blocking agent | A class of drugs that inhibit (block) a biologic activity or process, such as axonal conduction or transmission, or ions across a cell membrane; frequently called "blockers." (05 Mar 2000) |
| alveolocapillary block | The presence of material that impairs the diffusion of gases between the air in the alveolar spaces and the blood in alveolar capillaries; block can be caused by oedema, cellular infiltration, fibrosis, or tumour, and results in undersaturation of peripheral arterial blood with oxygen. (05 Mar 2000) |
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| anterograde block | Conduction block of an impulse traveling anywhere in its ordinary direction, for example, from the sinoatrial node toward the ventricular myocardium. (05 Mar 2000) |
| arborization block | Intraventricular block supposedly due to widespread blockage in the Purkinje ramifications and manifested in the electrocardiogram by a pattern similar to bundle-branch block but with complexes of low amplitude. (05 Mar 2000) |
| atrioventricular block | <cardiology> A conduction disturbance that results in the inappropriate delay (or complete inability) of a electrical impulse, generated in the atria, to reach the ventricles (via the atrioventricular node). Clinical types are divided into first (nonserious), second and third degree (most serious). Some drugs may precipitate atrioventricular block (for example clonidine, methyldopa, verapamil). A permanent pacemaker may be required for a third degree (complete) heart block. (02 Jan 1998) |
| autonomic nerve block | Interruption of sympathetic pathways, by local injection of an anaesthetic agent, at any of four levels: peripheral nerve block, sympathetic ganglion block, extradural block, and subarachnoid block. (12 Dec 1998) |
| A-V block | <cardiology> A conduction disturbance that results in the inappropriate delay (or complete inability) of a electrical impulse, generated in the atria, to reach the ventricles (via the atrioventricular node). Clinical types are divided into first (nonserious), second and third degree (most serious). Some drugs may precipitate atrioventricular block (for example clonidine, methyldopa, verapamil). A permanent pacemaker may be required for a third degree (complete) heart block. (02 Jan 1998) |
| bone block | A surgical procedure in which the bone adjacent to the joint is modified to limit the motion of the joint mechanically; e.g., at the ankle joint to correct foot-drop by preventing extension below 90 |
| bundle-branch block | <cardiology, physiology> Abnormal conduction through one of the conductive branches which normally supply the right and left ventricles. Usually results in delayed conduction though either the right or left bundle branches where one ventricle is excited before the other because of absence of conduction in one of the branches of the bundle of His. Intraventricular block due to interruption of conduction in one of the two main branches of the bundle of His and manifested in the electrocardiogram by marked prolongation of the QRS complex; block of each branch has distinctive QRS morphology. (05 Mar 2000) |
| paracervical block anaesthesia | Regional anaesthesia of the cervix uteri by injection of local anaesthetic solution into tissues adjacent to the cervix. (05 Mar 2000) |
| genetic block | <biochemistry, molecular biology> An obstruction in a biochemical pathway caused by a mutation that has crippled production of an enzyme critical to the pathway. (07 May 1998) |
| partial heart block | Impulses penetrate the atrioventricular junction in some relation to the ventricular rate. Synonym: incomplete atrioventricular block. (05 Mar 2000) |
| retrograde block | Impaired conduction backward from the ventricles or A-V node into the atria. (05 Mar 2000) |
| peri-infarction block | An electrocardiographic abnormality associated with an old myocardial infarct and caused by delayed activation of the myocardium in the region of the infarct; characterised by an initial vector directed away from the infarcted region with the terminal vector directed toward it. (05 Mar 2000) |
| phase I block | Inhibition of nerve impulse transmission across the myoneural junction associated with depolarisation of the motor endplate, as in the muscle paralysis produced by succinylcholine. (05 Mar 2000) |
| phase II block | Inhibition of nerve impulse transmission across the myoneural junction unaccompanied by depolarisation of the motor endplate, as in the muscle paralysis produced by tubocurarine. (05 Mar 2000) |