Avian embryos develop within a hard eggshell which permits the measurement
of heart rate while maintaining an adequate gas exchange through the chorio
allantoic membrane. Heart rate has been determined from cardiogenic signals
detected either noninvasively, semi-invasively or invasively with various
transducers. Firstly, we reviewed these previously-developed methods and ex
perimental results on heart rate fluctuations in prenatal embryos. Secondly
, we presented new findings;on the development of heart rate fluctuations d
uring the last stages of incubation, with emphasis on the perinatal period,
which remained-to be studied. Three patterns of acceleration of the instan
taneous heart rate were unique to the external pipping period: irregular in
termittent large accelerations, short-term repeated large accelerations and
relatively long-lasting cyclic small accelerations. Besides these accelera
tion patterns, respiratory arrhythmia, which comprized oscillating patterns
with a period of 1-1.5 s, appeared during the external pipping period. Fur
thermore, additional oscillating patterns with a period of 10-15 min were f
ound in some externally pipped embryos. (C) 1999 Elsevier Science Inc. All
rights reserved.