Cardiac rhythms in developing chicks

Kenji Moriya, Joachim Höchel, James T. Pearson, Hiroshi Tazawa

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Instantaneous heart rate (IHR) of chicks was determined by electrocardiogram measured non-invasively from the day of hatch to day 6 for continuity of investigation of HR fluctuations from embryos and for ascertainment of HR diurnal rhythms. In Experiment I, IHR was determined for 1-h periods twice a day, in daytime and at night, to investigate development of heart rate fluctuations (variability and irregularities). Chick IHR was substantially more arrhythmic than embryonic HR and spontaneous accelerations dominated HR fluctuations. Chick HR fluctuations were categorized into three types; [1] Type I as a widespread baseline HR (20-50 bpm) due to respiratory arrhythmia, with a mean oscillatory frequency of 0.74 Hz (range 0.4-1.2 Hz); [2] Type II as low frequency oscillations of baseline HR, at a mean of 0.07 Hz (range 0.04-0.10 Hz), and [3] Type III as non-cyclic irregularities, dominated by frequent transient accelerations. In Experiment II, continuous measurements of HR were made under conditions of a natural photoperiod, thermoneutrality and with feed available throughout the first week after hatching and circadian rhythms of HR were ascertained. HR was very variable in the daytime (250-500 bpm), due in part to feeding and activity, and decreased to a diurnal low (200-350 bpm) at night when mean HR was relatively stable. HR fluctuations persisted throughout the diurnal cycle.

Original languageEnglish
Pages (from-to)461-468
Number of pages8
JournalComparative Biochemistry and Physiology - A Molecular and Integrative Physiology
Issue number4
Publication statusPublished - 1 Dec 1999
Externally publishedYes


  • Chick
  • Circadian rhythm
  • Electrocardiogram
  • Heart rate fluctuations
  • Heart rate irregularities
  • Heart rate variability
  • Instantaneous heart rate
  • Spectrum analysis

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