Non-invasive determination of instantaneous heart rate in developing avian embryos by means of acoustocardiogram.

Previous noninvasive studies of the mean heart rate of embryonic birds have prompted an investigation into the instantaneous heart rate (IHR), which may be informative in developmental studies of cardiac rhythm. Using the acoustocardiogram (ACG), a noninvasive, long-term measuring system for embryonic IHR is developed, and the IHR in chickens during the last half of embryonic development is determined. The system, which uses a micro-computer, samples the ACG at a frequency of 50 Hz, restores the ACG wave by sinc function and calculates the IHR with an error in accuracy of less than 1 beat min-1. It was found that characteristic, transient bradycardia begins to appear late in the second week of incubation, and, with the additional development of transient tachycardia, the embryonic cardiac rhythm becomes more arrhythmic towards hatching. Simultaneous measurements of IHR with somatic movements showed no relationship between arrhythmia and embryonic activities. This system is useful, providing new evidence on long-term IHR developmental patterns.