Resonant Frequency Heart
The cardiac system, like most biological systems, demonstrates constant variation when in a healthy (or homeostatically balanced) state. It has long been postulated that heart rates that are "chaotic" or unpredictable are healthier than very steady rates. In recent years, we have acquired more understanding of the nature of variation in the human heart rate (or, more technically, in the interbeat interval "IBI"). Giardino, Lehrer, and Feldman (2000) and Berntson, Cacioppo, and Quigley (1993) present a detailed discussion of the meaning of oscillators and oscillations in biological systems. (In this chapter, as in several others, italics on first use of a term indicate that the term is included in the glossary at the chapter's end.) A technical review of variability in heart rate is presented by Berntson, Cacioppo, Quigley, and Fabro (1994) and Berntson et al. (1997).
In the last 10 years, due to improved technology in physiological measurement, there has been much interest in the relationship of heart rate variation and health outcomes. Decreased heart rate variability has been associated with increased cardiac mortality and morbidity (Bigger, Fleiss, Rolnitzky, & Steinman, 1993a, 1993b; Bigger, Rolnitzky, Steinman, & Fleiss, 1994; Bigger et al., 1995; Bigger, Steinman, Rolnitzky, Fleiss, & Albrecht, 1996) and a host of other poor health outcomes (Kleiger, Miller, Bigger, & Moss, 1987; Kristal-Boneh, Raifel, Harari, Malik, & Ribak, 1995; Katz, Liberty, Porath, Ovsyshcher, & Prystowsky, 1999; Kristal-Boneh, Froom, Raifel, Froom, & Ribak, 2000).
A measure of variability, usually the standard deviation of the R-wave to R-wave IBI, is indicative of autonomic control of the heart and perhaps also the lungs, the gut, and certain facial muscles. There are two pathways within the autonomic nervous system controlling the pacing of the heart rhythm: the sympathetic and parasympathetic.
The two systems interact in a complex synergistic relationship that is sometimes reciprocal, sometimes additive, and sometimes subtractive. Particular rhythms characteristic of each of them operate through these pathways. Porges (1995a, 1995b, 1997) has postulated that the vagus nerve in humans evolved to two pathways, originating from two medullary nuclei called the vagal nuclei. The first pathway, more primitive and older in evolutionary terms,