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(Circulation. 1999;100:e64.)
© 1999 American Heart Association, Inc.

Circulation Electronic Pages

Mathematical Treatment of Autonomic Oscillations - 2

J. Andrew Taylor, PhD

Assistant Professor of Medicine Harvard Medical School, Director, Laboratory for Cardiovascular Research, HRCA Research and Training Institute, Boston, Mass

Christopher W. Myers, PhD

Shuman Cardiovascular Research Fellow HRCA Research and Training Institute, Boston, Mass

	Introduction

 
To the Editor:

Recently, Montano et al¹ claimed a central vagotonic effect of high-dose atropine was evidenced in peroneal nerve muscle sympathetic outflow (MSNA). However, the authors' conclusions critically depend on "normalized units" to quantify low-frequency (LF) and high-frequency (HF) oscillations, a practice that can impart significance to the fluctuations beyond the regulatory mechanisms they subserve. This led to the conclusion that insight into parasympathetic nervous outflow can be gleaned from activity in a sympathetic nerve. We take issue with the interpretation of these data and believe that despite cautionary argument,² this approach subsumes the physiological meaning of cardiovascular oscillations to their spectral measures.

Heart period oscillations primarily derive from beat-by-beat autonomic control of systemic hemodynamics, ultimately buffering or augmenting arterial pressure fluctuations.³ Vascular sympathetic rhythms have been identified also, although they may or may not be related directly to pressure fluctuations.^{4 5} Spectral analysis conveniently quantifies these rhythms but in itself does not reveal their source. The findings of Montano et al rely solely on "normalizing" power spectral data, a technique that uncouples the oscillations from their physiological significance by measuring LF and HF relative to each other and making absolute amplitude irrelevant. In the present study, average heart period variance after atropine was <1% of control, representing almost complete elimination of beat-by-beat cardiac autonomic regulation. However, normalized units indicated that high-dose atropine reduced HF variability by only two thirds and increased LF variability by one third, divorcing spectral measures from the oscillations' minimal physiological significance. It is unclear how . . . [Full Text of this Article]

Nicola Montano, MD, PhD; Chiara Cogliati, MD; Alberto Porta, MD; Massimo Pagani, MD; Alberto Malliani, MD

Centro L.I.T.A. di Vialba, Centro Ricerche Cardiovascolari, CNR, Medicina Interna II, Ospedale L. Sacco, Università di Milano, Milano, Italy

Krzysztof Narkiewicz, MD, PhD; Francois M. Abboud, MD; Virend K. Somers, MD, PhD

Cardiovascular Division, Department of Internal Medicine, College of Medicine, University of Iowa, Iowa City, Iowa