© 2001 by European Society of Cardiology
Copyright © 2001, European Society of Cardiology
Autonomic indexes based on the analysis of heart rate variability: a view from the sinus node
aDipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Piazza della Scienza 2, Room U3-3013, 20126 Milan, Italy
bCardiologia, Dipartimento di Medicina, Chirurgia e Odontoiatria, Ospedale San Paolo, Università di Milano, Milan, Italy
* Corresponding author. Tel.: +39-02-6448-3307; fax: +39-02-6448-3565 antonio.zaza{at}unimib.it
Objective: Clinical indexes of autonomic activity are based on the analysis of sinus cycle length and of its variability. A common assumption underlying this practice is that neural activity and cycle length may be linearly related. Recent experimental evidence suggests that such an assumption may not be correct; indeed, the relation linking autonomic agonist concentration to cycle length was found to be strongly non-linear in single sinoatrial myocytes. In the present work, we (i) test compatibility of non-linearity of neural modulation of cycle length (CL) with previous experimental and clinical observations; (ii) evaluate its implications for what concerns the interpretation of time- and frequency-domain parameters of heart rate variability (HRV) and baroreflex sensitivity (BRS). Conclusions: Non-linearity of neural modulation of CL may result in an intrinsic rate-dependency of autonomic indexes, with the exception of normalised frequency-domain indexes (e.g. the low frequency/high frequency (LF/HF) ratio), which appear to be devoid of intrinsic rate-dependency. This characteristic may not limit the value of HRV indexes and BRS in risk stratification, but has to be taken into account in their pathophysiological interpretation.
KEYWORDS Autonomic nervous system; Baroreflex; Heart rate (variability)
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