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Cardiac rhythms in developing emu hatchlings
K Moriya1, K Kato, M Matsumura
1Department of Electrical and Electronic Engineering, Muroran Institute of Technology, 050-8585, Muroran, Japan.
Insights
Emu hatchlings exhibit unique heart rate variability, including distinct accelerations and oscillations, unlike chick hatchlings. Their breathing rate is also slower, and they lack a clear circadian rhythm in their first week.
Area of Science:
- Cardiovascular physiology
- Avian biology
- Comparative physiology
Background:
- Understanding avian cardiovascular development is crucial for species conservation and biomedical research.
- Previous studies have characterized heart rate patterns in chick hatchlings, providing a baseline for comparison.
Purpose of the Study:
- To characterize the heart rate variability and developmental patterns in emu hatchlings during their first week of life.
- To compare the electrocardiogram (ECG) and heart rate (HR) characteristics of emu hatchlings with those of chick hatchlings.
Main Methods:
- Non-invasive electrocardiogram (ECG) recordings were obtained from six emu hatchlings using flexible chest wall electrodes.
- Instantaneous heart rate (IHR) was determined from ECG data throughout the first week post-hatching.
- Heart rate variability patterns (Types I, II, III, and unique accelerations) and mean heart rate (MHR) were analyzed.
- Breathing frequency was estimated from respiratory sinus arrhythmia (RSA).
- Circadian rhythmicity of MHR was assessed using visual inspection and power spectrum analysis.
Main Results:
- Emu hatchlings displayed low baseline heart rates (100-200 bpm) with significant fluctuations and unique large accelerations.
- Distinct heart rate oscillations (Type I: 0.37 Hz RSA, Type II: 0.06 Hz) were observed, with RSA suggesting slower breathing compared to chickens.
- Unlike chick hatchlings, emu hatchlings did not exhibit a clear circadian rhythm in MHR during the first week.
- Large, irregular heart rate accelerations were a characteristic finding in emu hatchlings.
Conclusions:
- Emu hatchlings possess a distinct cardiovascular profile characterized by significant heart rate variability and unique accelerations.
- The respiratory sinus arrhythmia suggests a lower breathing frequency in emus compared to chickens, indicating developmental differences.
- The absence of a clear circadian rhythm in early life may reflect unique thermoregulatory or developmental strategies in emu hatchlings.
Abstract:
Six emu hatchlings were non-invasively measured for electrocardiogram (ECG) from their chest wall using flexible electrodes, and the instantaneous heart rate (IHR) was determined from ECG throughout the first week of post-hatching life. Although the baseline heart rate (HR) was low, approximately 100-200 beats per min (bpm), compared with chick hatchlings, the IHR fluctuated markedly. The fluctuation of IHR comprised HR variability and irregularities that were designated as types I, II and III in chick hatchlings and additional large accelerations distinctive of emu hatchlings. Type I was HR oscillation with a mean frequency of 0.37 Hz (range 0.2-0.7 Hz), i.e. respiratory sinus arrhythmia (RSA). From RSA, breathing frequency in emu hatchlings was estimated to be approximately half of that in chickens. Type II HR oscillation was also found in the emu; the frequency ranged from approximately 0.04 to 0.1 with a mean of 0.06 Hz, and the magnitude tended to be large compared with that of chickens. In addition to type III HRI, which was designated in chickens, large, irregular HR accelerations were characteristic of emu hatchlings. From IHR data, developmental patterns of mean heart rate (MHR) were constructed and plotted on a single graph to inspect the diurnal rhythm of MHR by visual inspection and power spectrum analysis. A circadian rhythm was not clear in the emu hatchlings, in contrast to chick hatchlings, which showed a dominant diurnal rhythm.