Cardiac rhythms in chick embryos during hatching

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.