1 1 N ov 1 99 9 The RR interval spectrum , the ECG signal and aliasing

We discuss the relationship between the RR interval spectral analysis and the spectral analysis of the corresponding ECG signal from which the RR intervals were evaluated. The ECG signal spectrum is bounded below the frequency f B by using an electronic filter and sampled at rate larger than 2f B , thus excluding aliasing from spectral analysis. A similar procedure cannot be applied to the RR interval spectral analysis, and in this case aliasing is possible. One of our main effort in this paper is devoted to the problem of how to detect aliasing in the heart rate spectral analysis. In order to get an insight we performed an experiment with an adult man, in which the ECG signal was detected in a case where the breathing rate was larger than half the heart rate. A constant breathing rate for time intervals exceeding 5 minutes was monitored with good accuracy using a special breathing procedure. The results show distinctively a very sharp peak in the spectral analysis of the ECG signal and corresponding (diffused) aliasing peaks in the RR interval spectral analysis. New method of dealing with unevenly sampled data was developed which has interesting anti-aliasing properties. There are indications that the VLF peaks of the RR spectrum are originated by aliasing. Some of the LF peaks may have the same property.