Heart rate responses to cooling in emu hatchlings.
Among fluctuations of instantaneous heart rate (IHR) in newly hatched chicks, heart rate (HR) oscillation with a mean frequency of 0.7 Hz has been designated as Type II HR variability characterized by low frequency (LF) oscillation [Comp. Biochem. Physiol. Part A 124 (1999) 461]. In response to exposure to lowered ambient temperature (Ta), chick hatchlings raised their HR baseline accompanied with the production or augmentation of Type II HR oscillation, indicating that LF oscillation is a phenomenon relating to thermoregulation [J. Therm. Biol. 26 (2001) 281]. In emu hatchlings that are precocial like chickens, Type II HR oscillation also occurred, but less frequently in comparison with chick hatchlings [Comp. Biochem. Physiol. Part A 131 (2002) 787]. This present experiment was conducted to elucidate how IHR of emu hatchlings responds to changes in Ta. Six hatchlings were measured for IHR and skin temperature (Ts) during a 3-h period when they were exposed to controlled Ta (ca. 35 degrees C), lowered Ta (ca. 15-30 degrees C) and again the controlled Ta for individual 1-h periods. In response to all the cooling and re-warming procedures, HR baseline changed depending upon the intensity of the Ta differences; i.e. large differences of Ta produced large changes in HR. HR fluctuations tended to augment during cooling with a few exceptions, but LF oscillation was not produced. Thus, LF oscillation, which was scarce even at the controlled Ta, could not be used as a thermoregulatory indicator in emus.
Tamura
A
A
Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan.
Akiyama
R
R
Chiba
Y
Y
Moriya
K
K
Dzialowski
E M
EM
Burggren
W W
WW
Tazawa
H
H
D000818:Animals; D003080:Cold Temperature; D020312:Dromaiidae / Q000502:physiology*; D006339:Heart Rate