Long-term measurement of heart rate in XXXX eggs.

@entity591 @entity1573 @entity1168 @entity299
Taking advantage of acoustocardiogram (ACG), we measured the heart rate (HR) of @entity1573 embryos continuously from day 12 until hatching and then investigated the development of @entity299 (HRV), and the existence of a circadian rhythm in mean HR (MHR). HRI comprised transient @entity1168 and @entity591 , which first developed on day 14 and 16 in most embryos, respectively. Transient @entity1168 increased in frequency and magnitude with embryonic development and occurred over periods of up to 30 min in some embryos. MHR was maximal on around days 14-15 and thereafter decreased to about 250-260 bpm on days 16-18. Baseline HRV, which is an oscillation of the MHR baseline, occurred as HR decreased from days 15-16 and became predominant on days 17-18. The magnitude of the baseline oscillations reached up to 50 bpm in some embryos and the period ranged between about 40-90 min (ultradian rhythm). A circadian rhythm of MHR was not found in late @entity1573 embryos. On days 18-19, embryonic activities were augmented and then breathing movements began to occur, disturbing ACG signals and thus making it difficult to measure the HR. Instead, the development of breathing activities was recorded. Breathing frequency was irregular at first and then increased to a maximum of about 1.5 Hz prior to hatching.
