Evidence of a previously undescribed form of respiratory sinus arrhythmia (RSA)--the physiological manifestation of "cardiac aliasing".

Within the fluctuations that occur in heart rate, there is a major component known as respiratory sinus arrhythmia (RSA), which up to now has been defined as heart rate variability which is synchronous with respiratory movements. We have now discovered that RSA synchronous to respiratory movements is only one example of RSA. If a special relationship exists between mean heart rate (fHR) and mean frequency of breathing (fB) such that fB greater than 1/2 fHR, RSA can be observed in a frequency range which is lower than the frequency of breathing. The mathematical fundamentals of this physiological phenomenon are the same as those for the "aliasing"-effect in signal sampling. Therefore, we have called this phenomenon "cardiac aliasing". We have been able to experimentally demonstrate this, up to now unknown, phenomenon in adult rabbits and dogs as well as in human neonates.