Complex demodulation of heart rate variability during parabolic flight: an exploratory study

The aim of this study was to evaluate the usefulness of complex demodulation (CDM) in assessing frequency components of heart rate variability (HRV) in the setting of dynamic amplitude variations. First, analysis of simulated data showed that the upper limit of rapid amplitude variations corresponded to a period of less than 16 s in order to allow a 95% reliable LF and HF estimation. Second, in terms of estimating the mean LF-to-HF ratio in healthy subjects, CDM was equivalent to FFT power spectrum analysis (r=.97; p<0.001). Finally, CDM was applied during parabolic flight to determine time-dependent responses of respiratory sinus arrhythmia (RSA) as a function of gravity. Postural differences in both heart rate and RSA were augmented during hypergravity conditions and abolished at 0 Gz of parabolic flight. These results show that CDM can be used to provide a continuous reliable assessment of dynamic autonomic cardiovascular control