The Beatquency Domain: An Unusual Application of the Fast Fourier Transform

Fourier analysis has proven to be a vital mathematical tool in many areas of research, but rapid methods for calculating frequency content of sampled data using discrete Fourier transform (FFT) require periodic sampling. Unfortunately, beat-by-beat heart rate is an aperiodic series of events in the time domain. This report describes a new and unusual application of the FFT on heart rate data. The beat-by-beat intervals are represented as the magnitude of a periodically sampled function. When the Fourier transform is applied to these data, we obtain pseudofrequency information from what we call the Beat-quency Domain. Observed patterns from the Beatquency Domain suggest usefulness of this method in sleep cycle detection.