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dissociation (di-so-se-a´shun, -she-a´shun)

1. Separation, or a dissolution of relations.disassociation; 2. The change of a complex chemical compound into a simpler one by any lytic reaction or by ionization. 3. An unconscious process by which a group of mental processes is separated from the rest of the thinking processes, resulting in an independent functioning of these processes and a loss of the usual relationships; for example, a separation of affect from cognition. See multiple personality. [L. dis-socio, pp. -atus, to disjoin, separate, fr. socius, partner, ally]
albuminocytologic d. increased protein in the cerebrospinal fluid without increase in cell count, characteristic of the Guillain-Barré syndrome; it is also associated with spinal block and with intracranial neoplasia, and is seen in the last phases of poliomyelitis.
atrial d. mutually independent beating of the two atria or of parts of the atria.
atrioventricular d. (AVD) , A-V d. 1. any situation in which atria and ventricles are activated and contract independently, as in complete A-V block; 2. more specifically, the d. between atria and ventricles that results from slowing of the atrial pacemaker or acceleration of the ventricular pacemaker at nearly equal (rarely equal) rates, each depolarizing its own chamber, thus interfering with depolarization by the other (interference-dissociation).
complete atrioventricular d. , complete A-V d. 1. A-V d. not interrupted by ventricular captures; 2. complete A-V block
electromechanical d. persistence of electrical activity in the heart without associated mechanical contraction; often a sign of cardiac rupture.
incomplete atrioventricular d. , incomplete A-V d. A-V d. interrupted by ventricular captures.
interference d. the simultaneous operation of two separate cardiac pacemaking foci that are unassociated because of interference (a normal physiologic phenomenon) due to rendering their respective territories refractory to each other. Usually atrioventricular d. is indicated, the rates being quite close to each other with the atrial rate slightly faster than that of the pacemaker in control of the ventricles. Capture is in either direction, usually the ventricle by the atrium, in incomplete d. hd. by interference;
d. by interference interference d
isorhythmic d. A-V d. characterized by equal or closely similar atrial and ventricular rates.
light-near d. pupillary light-near dissociation
longitudinal d. d. between parallel chambers of the heart, as between one atrium and the other or between one ventricle and the other, in contrast to d. between atria and ventricles.
pupillary light-near d. See pupillary light-near dissociation.
sleep d. sleep paralysis
syringomyelic d. loss of pain and temperature sensation with relative retention of tactile sensation, related to a cavity in the central portion of the cord interrupting the decussation of nerve fibers.
tabetic d. loss of proprioceptive sensation with retained pain and temperature sensation due to involvement of the posterior columns of the spinal cord.


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