circadian rhythm - definition of circadian rhythm in the Medical dictionary - by the Free Online Medical Dictionary, Thesaurus and Encyclopedia.

rhythm (rithm) a measured movement; the recurrence of an action or function at regular intervals.rhyth´micrhyth´mical

alpha rhythm electroencephalographic waves having a uniform rhythm and average frequency of 10 per second, typical of a normal person awake in a quiet resting state.

atrial escape rhythm a cardiac dysrhythmia occurring when sustained suppression of sinus impulse formation causes other atrial foci to act as cardiac pacemakers.

atrioventricular (AV) junctional rhythm the heart rhythm that results when the atrioventricular junction acts as pacemaker.

atrioventricular (AV) junctional escape rhythm a cardiac rhythm of four or more AV junctional escape beats at a rate below 60 beats per minute.

beta rhythm electroencephalographic waves having a frequency of 18 to 30 per second, typical during periods of intense activity of the nervous system.

circadian rhythm the regular recurrence in cycles of approximately 24 hours from one stated point to another, e.g., certain biological activities that occur at that interval regardless of constant darkness or other conditions of illumination.

coupled rhythm heart beats occurring in pairs, the second beat usually being a ventricular premature beat; see also bigeminal pulse.

delta rhythm rhythm on the electroencephalogram consisting of delta waves.

ectopic rhythm a heart rhythm initiated by a focus outside the sinoatrial node.

escape rhythm a heart rhythm initiated by lower centers when the sinoatrial node fails to initiate impulses, when its rhythmicity is depressed, or when its impulses are completely blocked.

gallop rhythm an auscultatory finding of three (triple r.) or four (quadruple r.) heart sounds; the extra sounds occur in diastole and are related either to atrial contraction (S), to early rapid filling of a ventricle (S), or to concurrence of both events (summation gallop) .

idioventricular rhythm a sustained series of impulses propagated by an independent pacemaker within the ventricles, with a rate of 20 to 50 beats per minute.

infradian rhythm the regular recurrence in cycles of more than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination.

nodal rhythm atrioventricular junctional r.

pendulum rhythm alternation in the rhythm of the heart sounds in which the diastolic and systolic sounds are nearly identical and the heartbeat resembles the tick of a watch.

quadruple rhythm the gallop rhythm cadence produced when all four heart sounds recur in successive cardiac cycles.

reciprocal rhythm a cardiac dysrhythmia established by a sustained reentrant mechanism in which impulses traveling back toward the atria also travel forward to reexcite the ventricles, so that each cycle contains a reciprocal beat, with two ventricular contractions.

reciprocating rhythm a cardiac dysrhythmia in which an impulse initiated in the atrioventricular node travels toward both the atria and ventricles, followed by cycles of bidirectional propagation of the impulse alternately initiating from those impulses traveling up and those traveling down.

reentrant rhythm an abnormal cardiac rhythm resulting from reentry.

sinoatrial rhythm , sinus rhythm the normal heart rhythm originating in the sinoatrial node.

supraventricular rhythm any cardiac rhythm originating above the ventricles.

theta rhythm rhythm on the electroencephalogram consisting of theta waves.

triple rhythm the cadence produced when three heart sounds recur in successive cardiac cycles; see also gallop r.

ultradian rhythm the regular recurrence in cycles of less than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination.

ventricular rhythm

1. idioventricular r.

2. any cardiac rhythm controlled by a focus within the ventricles.

circadian rhythm

A daily rhythmic activity cycle, based on 24-hour intervals, that is exhibited by many organisms.

Circadian rhythm

Any body rhythm that recurs in 24-hour cycles. The sleep-wake cycle is an example of a circadian rhythm.

Mentioned in: Phototherapy, Sleep Disorders

circadian rhythm

Etymology: L, circa, about, dies, day; Gk, rhythmos, rhythm

a pattern based on a 24-hour cycle, especially the repetition of certain physiologic phenomena, such as sleeping and eating.

circadian rhythm,

n person's biological patterns within a 24-hour cycle, circa a day. See also chronobiology.

circadian

denoting a period of about 24 hours.

circadian clock

the daily rhythm of physiological activity as expressed by the Chinese circadian clock. This explains the flow of energy or Qi through the body, via the meridians, each meridian having two hours of maximum and two of minimum function in every day.

circadian rhythm

the regular recurrence of certain phenomena in cycles of approximately 24 hours, e.g. biological activities that occur at about the same time each day (or night) regardless of constant darkness or other conditions of illumination.

rhythm

a measured movement; the recurrence of an action or function at regular intervals.

alpha rhythm

a uniform rhythm of waves in the normal electroencephalogram.

beta rhythm

a rhythm in the electroencephalogram consisting of waves smaller than those of the alpha rhythm, having an average frequency of 25 per second, typical during periods of intense activity of the nervous system. See also electroencephalography.

biological r's

the cyclic changes that occur in physiological processes of living organisms; called also biorhythms. These rhythms are so persistent throughout the living kingdom that they probably should be considered a fundamental characteristic of life, as are growth, reproduction, metabolism and irritability. Many of the physiological rhythms occur in animals about every 24 hours (circadian rhythm). Examples include the peaks and troughs that are manifested in body temperature, vital signs, brain function and muscular activity. Biochemical analyses of urine, blood enzymes and plasma serum also have demonstrated rhythmic fluctuations in a 24-hour period.

It has long been believed that the cyclic changes observed in plants and animals were totally in response to environmental changes and, as such, were exogenous or of external origin. This hypothesis is now being rejected by some chronobiologists who hold that the biological rhythms are intrinsic to the organisms, and that the organisms possess their own physiological mechanism for keeping time. This mechanism has been called the 'biological clock'.

circadian rhythm

see circadian rhythm.

circamensual rhythm

that which occurs in cycles of about one month (30 days).

circannual rhythm

the recurrence of a phenomenon in cycles of about one year.

circaseptan rhythm

that which occurs in cycles of about 7 days (one week).

coupled rhythm

heartbeats occurring in pairs, the second beat of the pair usually being a ventricular premature beat.

escape rhythm

a heart rhythm initiated by lower centers when the sinoatrial node fails to initiate impulses, its rhythmicity is depressed, or its impulses are completely blocked.

gallop rhythm

an auscultatory finding of three or four heart sounds, the extra sounds by convention being in diastole and related to atrial contraction (fourth sound, presystolic gallop), to early rapid filling of a ventricle with an altered ventricular compliance (protodiastolic gallop), or to concurrence of atrial contraction and ventricular early rapid filling (summation gallop).

idioventricular rhythm

a series of ventricular escape complexes occuring at a regular rate.

infradian rhythm

the regular recurrence in cycles of more than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination.

nodal rhythm

heart rhythm initiated in the specialized junctional tissue, i.e. the atrioventricular node and the main (His) bundle.

nyctohemeral rhythm

a day and night rhythm.

pendulum rhythm

alternation in the rhythm of the heart sounds in which the diastolic sound is equal in time, character and loudness to the systolic sound, the beat of the heart resembling the tick of a watch.

sinus rhythm

normal heart rhythm originating in the sinoatrial node.

Electrocardiogram showing normal sinus rhythm in a dog. By permission from Darke P, Kelly DF, Bonagura JD, Color Atlas of Veterinary Cardiology, Mosby, 1995

ultradian rhythm

the regular recurrence in cycles of less than 24 hours, as certain biological activities which occur at such intervals, regardless of conditions of illumination.

ventricular rhythm

the ventricular contractions which occur in cases of complete heart block.

rhythm, circadian

The characteristic of some processes to repeat at approximately 24-hour intervals. Examples: intraocular pressure is at its lowest every evening and highest every morning; corneal sensitivity is at its lowest every morning and highest every evening. Syn. diurnal cycle (provided the variation in activity or behaviour is more or less divided equally between night and day). See melanopsin.

circadian rhythm

Diurnal rhythm, ultradian rhythm Physiology An innate, daily, fluctuation of physiologic and behavioral functions–eg sleep waking, generally tied to the 24 hr day-night cycle; the diurnal cadence in humans without cyclical cues provided by natural light, is 25.4 hrs; CR affects drug metabolism, serum levels of various substances–eg, ACTH, physiologic activities–eg, BP, myocardial blood flow and O₂ demand, psychosomatic disease and sleep cycles, cell division, hematopoiesis, NK cell activity. See Biorhythm, Circadian pacemaker, Insomnia, Jet lag, Melatonin, Shift work.