| Wolff-Chaikoff block | Blocking of the organic binding of iodine and its incorporation into hormone caused by large doses of iodine; usually a transient effect, but in large doses in susceptible individuals it can be prolonged and cause iodine myxoedema. Synonym: Wolff-Chaikoff effect. (05 Mar 2000) |
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| conduction block | Failure of impulse transmission at some point along a nerve, although conduction along the segments proximal and distal to it are unaffected. Clinically, most often caused by an area of focal demyelination; when caused by focal trauma, called neurapraxia. (05 Mar 2000) |
| congenital heart block | Atrioventricular block present in utero or at birth and usually of advanced or complete degree. (05 Mar 2000) |
| hanging-block culture | The propagation of microorganisms on a cube of solidified agar medium which is inoculated, attached to a cover glass, and inverted over a moist chamber or hollowed slide. (05 Mar 2000) |
| saddle block anaesthesia | A form of spinal anaesthesia limited in area to the buttocks, perineum, and inner surfaces of the thighs. Synonym: saddle anaesthesia. (05 Mar 2000) |
| heart block | <cardiology, physiology> 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) AV blocks. Some drugs may precipitate an AV block (for example clonidine, methyldopa, verapamil). A permanent pacemaker may be required for a third degree (complete) heart block. (07 Apr 1998) |
| protective block | An incompletely understood mechanism whereby a pacemaker is protected from being discharged by the impulse from another centre; the mechanism, usually conceived as an encircling zone of unidirectionally refractory tissue permitting egress of impulses from the centre but preventing access to the centre, is seen in operation in ventricular parasystole where the parasystolic centre is protected from discharge by the sinus pacemaker and so is able to maintain its intrinsic rhythm undisturbed. Synonym: entrance block, protection. (05 Mar 2000) |
| second degree A-V block | See: atrioventricular block. (05 Mar 2000) |
| pupillary block glaucoma | Glaucoma secondary to failure of the aqueous humor to pass through the pupil to the anterior chamber. (05 Mar 2000) |
| sinoatrial block | <cardiology, physiology> Disturbance of heart conduction in which the atrial response is delayed or omitted because of partial or complete interference with the propagation of impulses from the sinoatrial node to the atria. (12 Dec 1998) |
| sinoauricular block | <cardiology, physiology> Disturbance of heart conduction in which the atrial response is delayed or omitted because of partial or complete interference with the propagation of impulses from the sinoatrial node to the atria. (12 Dec 1998) |
| spinal block | An obstruction to the flow of cerebrospinal fluid in the spinal subarachnoid space; used inaccurately to refer to spinal anaesthesia. (05 Mar 2000) |
| stellate block | Injection of local anaesthetic solution in the vicinity of the stellate ganglion. (05 Mar 2000) |
| neurolytic block | <procedure> The injection of a chemical agent to cause destruction and consequent prolonged interruption of peripheral somatic or sympathetic nerves or in some cases, the neuraxis. (16 Dec 1997) |
| nondepolarising block | Skeletal mucle paralysis unaccompanied by changes in polarity of the motor endplate, as occurs following administration of tubocurarine. (05 Mar 2000) |