J Appl Physiol 102: 1716, 2007.
First published December 28, 2006; doi:10.1152/japplphysiol.01446.2006
8750-7587/07 $8.00
POINT-COUNTERPOINT COMMENTS
Dirk Cysarz
Medical Theory and Complementary Medicine
University of Witten/Herdecke and
Integrated Studies of Anthroposophical Medicine
Herdecke, Germany
e-mail: d.cysarz{at}rhythmen.de
The following letter is in response to the Point:Counterpoint "Cardiovascular variability is/is not an index of autonomic control of circulation" that appeared in the August 2006 issue (vol 101: 676–682, 2006; http://jap.physiology.org/cgi/content/full/101/2/676).
To the Editor: In principle, the analysis of heart rate variability (HRV) via spectral analysis offers the ability to quantify the amount of the modulation of both branches of the autonomic nervous system (4). Obviously, the physiological interpretation of the results of HRV analysis is more precise if the confounding factors are minimized. Hence, the experimental conditions need different methodological (e.g., steady-state conditions imposed by the spectral analysis) as well as physiological constraints (e.g., control of respiration). Such restrictions are often difficult to realize. Furthermore, the extrapolation of results obtained under restricted conditions to everyday conditions (such as, e.g., obtained from ambulatory Holter recordings) is limited. To overcome these shortcomings different methodological improvements have been proposed, e.g., refinements of the spectral analysis (3).
Interestingly, the physiological interpretation of cardiovascular variability is essentially based on linear methods, especially spectral analysis. The oscillatory model seems to be adequate to quantify the modulations of the two branches of the autonomic nervous system. However, the various limitations of this model show its shortcomings and, hence, call for complementary approaches. The physiological interpretation of most nonlinear methods (e.g., approximate entropy) is still limited because the mathematical formalism underlying such methods cannot be transformed easily into physiological models of the autonomic nervous system. Nevertheless, there are other methods that probably could be interpreted in terms of physiology more easily. One example is the analysis of symbolic dynamics reflecting acceleration and deceleration of instantaneous heart rate. Such dynamics may be relatively easy to interpret and also supply additional information (1, 2). The refinement of the physiological interpretation of cardiovascular variability is not only a matter of constraints imposed by accepted methods but also depends on the potential physiological interpretation based on linear and nonlinear methods.
REFERENCES
- Bettermann H, Amponsah D, Cysarz D, Van Leeuwen P. Musical rhythms in heart period dynamics—a cross-cultural and interdisciplinary approach to cardiac rhythms. Am J Physiol Heart Circ Physiol 277: H1762–H1770, 1999.[Abstract/Free Full Text]
- Cysarz D, Lange S, Matthiessen PF, Van Leeuwen P. Regular heartbeat dynamics are associated with cardiac health. Am J Physiol Regul Integr Comp Physiol 292: R368–R372, 2007.[Abstract/Free Full Text]
- Mateo J, Laguna P. Improved heart rate variability signal analysis from the beat occurrence times according to the IPFM model. IEEE Trans Biomed Eng 47: 985–996, 2000.[CrossRef][ISI][Medline]
- Parati G, Mancia G, Rienzo MD, Castiglioni P. Point:Counterpoint: Cardiovascular variability is/is not an index of autonomic control of circulation. J Appl Physiol 101: 676–678, 2006.[Abstract/Free Full Text]
Copyright © 2007 by the American Physiological Society.
