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Continuous measurements of instantaneous heart rate and its fluctuations before and after hatching in chickens
K Moriya1, J T Pearson, W W Burggren
1Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan.
Insights
Heart rate fluctuations in chick embryos show complex patterns during development and hatching. These distinct changes in fetal heart rate (fh) offer insights into cardiovascular control and developmental physiology.
Area of Science:
- Developmental Physiology
- Cardiovascular Research
- Embryology
Background:
- Heart rate (fh) fluctuations are studied in mammalian fetuses and avian embryos.
- Avian embryos serve as a model for developmental physiology research.
Purpose of the Study:
- To determine instantaneous fh in chick embryos from late prenatal development through hatching.
- To analyze fh patterns during the perinatal period and early post-hatching stages.
Main Methods:
- Continuous monitoring of instantaneous fh in seven chick embryos.
- Observation from day 18 of prenatal development up to day 2 post-hatching.
Main Results:
- Distinct fh fluctuation patterns observed, including cyclic oscillations (ultradian rhythm) and baseline shifts.
- Emergence of specific accelerations (cyclic, irregular, short-term) during pipping.
- Post-hatching, a circadian rhythm and previously reported fh fluctuations (types I-III) appeared.
- Developmental patterns were unaffected by hatching failure.
Conclusions:
- Complex and repeatable fh fluctuation patterns change significantly during avian embryonic development.
- The avian embryo model is valuable for studying fh fluctuation phenomena and their physiological underpinnings.
Abstract:
There has been considerable interest in heart rate (fh) fluctuations in relation to cardiovascular control systems and foetal conditions during pregnancy in mammals. Prominent fluctuations in fh also occur in avian embryos, which are an important experimental model for studying developmental physiology. The present study determined the instantaneous fh of seven chick embryos continuously from the last stage of prenatal development (day 18), throughout the pipping (perinatal) period (days 19-21) until hatching and, subsequently, of newly hatched chicks (up to day 2). The distinctive patterns of instantaneous fh fluctuations took the form of specific changes within a broad mean fh baseline. Cyclic oscillations (ultradian rhythm) occurred until an early stage of the perinatal period, when the fh baseline started rising. Subsequently, the baseline dropped and respiratory arrhythmia began to appear concomitant with external pipping. During the final stage of external pipping, when the fh baseline rose again prior to hatching, three unique patterns of instantaneous fh fluctuations were evident: relatively long-lasting cyclic small accelerations, irregular intermittent large accelerations and short-term repeated large accelerations. Furthermore, repeated alternate occurrences of the latter two types of acceleration formed an additional oscillating pattern with a period of 10-15 min. During the early period after hatching, when the fh baseline reached its maximum, instantaneous fh changed relatively slowly accompanied by transient rapid decelerations, probably due to augmented vagal tone. Subsequently, the mean fh baseline dropped to its minimum, and a circadian rhythm and three types of previously reported fh fluctuations (types I-III) appeared. Developmental patterns of mean fh and the appearance of distinctive patterns of instantaneous fluctuations in fh and circadian rhythms were not influenced by an ultimate failure of hatching after a normal development. The demonstration of complex, repeatable patterns of fh fluctuation that change during development suggests that the avian embryo model should be useful in studying the phenomenon of fh fluctuation and its underlying causes.