Critical analysis of autoregressive and fast Fourier transform markers of cardiovascular variability in rats and humans

G.J.J Silva,M.R Ushizima,I.A Cestari,P.S Lessa,H.F Lopes,J.E Krieger,E.M Krieger,M.M Atala,L.F Drager,F.M Consolim-Colombo,L Cardoso

doi:10.1590/s0100-879x2009000400012

Abstract

The autonomic nervous system plays an important role in physiological and pathological conditions, and has been extensively evaluated by parametric and non-parametric spectral analysis. To compare the results obtained with fast Fourier transform (FFT) and the autoregressive (AR) method, we performed a comprehensive comparative study using data from humans and rats during pharmacological blockade (in rats), a postural test (in humans), and in the hypertensive state (in both humans and rats). Although postural hypotension in humans induced an increase in normalized low-frequency (LFnu) of systolic blood pressure, the increase in the ratio was detected only by AR. In rats, AR and FFT analysis did not agree for LFnu and high frequency (HFnu) under basal conditions and after vagal blockade. The increase in the LF/HF ratio of the pulse interval, induced by methylatropine, was detected only by FFT. In hypertensive patients, changes in LF and HF for systolic blood pressure were observed only by AR; FFT was able to detect the reduction in both blood pressure variance and total power. In hypertensive rats, AR presented different values of variance and total power for systolic blood pressure. Moreover, AR and FFT presented discordant results for LF, LFnu, HF, LF/HF ratio, and total power for pulse interval. We provide evidence for disagreement in 23% of the indices of blood pressure and heart rate variability in humans and 67% discordance in rats when these variables are evaluated by AR and FFT under physiological and pathological conditions. The overall disagreement between AR and FFT in this study was 43%.

Highlights

The homeostasis of the cardiovascular system is efficiently maintained under control by feedback mechanisms that act to maintain perfusion pressure to the organs within a relatively narrow range of variation
The task force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology established the standardization of measurement, physiological interpretation, and clinical use of power spectral analysis [10], and the advantages and disadvantages of both parametric and nonparametric methods have been described by others [12]. In view of these considerations, we investigated the agreement of the AR and fast Fourier transform (FFT) methods regarding the extraction of autonomic markers during 1) postural changes in healthy volunteers, 2) pharmacological blockade of the autonomic nervous system to the heart in normal control rats, 3) in patients with arterial hypertension, and 4) in an experimental model of hypertension
The present study compared the agreement between the AR and FFT methods under several conditions: a physiological stimulus, postural changes induced in normal healthy volunteers or pharmacological blockade in an experimental model, and under pathological conditions, i.e., patients with mild and severe hypertension or a genetic experimental model of hypertension (SHR)

Summary

Introduction

The homeostasis of the cardiovascular system is efficiently maintained under control by feedback mechanisms that act to maintain perfusion pressure to the organs within a relatively narrow range of variation. The autonomic nervous system plays an important role in blood pressure regulation, producing adjustments in heart rate and myocardium contractility by altering sympathetic and parasympathetic activities to the heart, and peripheral vascular resistance and blood volume by constriction of arterial and venous vessels, respectively [1] These effects occur during each cardiac cycle and can be assessed by the variations in R-R intervals of the electrocardiogram. The spectral analysis components facilitated the physical interpretation of the mechanisms involved in the regulation of the cardiovascular system Later, these findings lent support to the sympathovagal balance hypothesis [5], whereby the normalized power of the low-frequency (LFnu) component of heart rate variability was associated with the sympathetic modulation and the high-frequency (HFnu) component was associated with parasympathetic modulation. This hypothesis was validated during postural changes (or orthostatic test) that impose perturbation on the cardiovascular system, revealing potential applications to assess physiological and physiopathological conditions

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Conclusion