POINT-COUNTERPOINTPoint-Counterpoint CommentsDirk CysarzDirk CysarzPublished Online:01 Apr 2007https://doi.org/10.1152/japplphysiol.01446.2006This is the final version - click for previous versionMoreSectionsPDF (25 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations 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.REFERENCES1 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.Link | ISI | Google Scholar2 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.Link | ISI | Google Scholar3 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 | PubMed | ISI | Google Scholar4 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.Link | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Cited ByDifferent equestrian sports horses’ reactivity to startleJournal of Veterinary Behavior, Vol. 57 More from this issue > Volume 102Issue 4April 2007Pages 1716-1716 Copyright & PermissionsCopyright © 2007 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.01446.2006PubMed17194728History Published online 1 April 2007 Published in print 1 April 2007 Metrics