Spectral analysis of blood pressure signal in conscious rats released from simulated microgravity

The aim of the present study was to examine whether there are changes in systolic and diastolic blood pressure (SBP and DBP) and heart rate (HR) and their spectral indices in conscious free-moving rats after tail-suspension for 28 d. The tail-suspended hindlimb-unloaded (HU) rat model was used to simulate the cardiovascular effect of microgravity and the post-spaceflight cardiovascular dysfunction. The auto- and cross-spectral analysis of SBP variability (SBPV) and HR variability (HRV) were performed by the method based on the autoregressive model (AR), and the auto-spectral results was compared with the results from the classical periodogram method. The baroreceptor-heart rate reflex sensitivity (BRS) was estimated using transfer function analysis from SBP to HR. The results indicated that auto-spectral results based on the two methods were comparable, while smoother power spectral curves with distinguished peaks were trained by the AR method. The means of SBP, DBP, and HR, the main spectral indices of SBPV