Quantitative Respiratory Sinus Arrhythmia Analysis

Multifrequency resonance structure is a basic biological property that confers stability upon oscillating systems. The relationship of the oscillating respiratory and cardiac systems can be characterized by a series of rhythms including the fundamental frequency, the respiratory sinus arrhythmia (Hz 0.12-0.16), slightly lower frequencies 0.04-0.8, as well as very low frequency components q 90 min, q 4-6 h, q 8-12 h, and circadian. Quantitative measurement of the fundamental frequency, the respiratory sinus arrhythmia, can yield important preventative and diagnostic information about the heart, the chest and lungs, as well as the autonomic nervous system. This sort of analysis has demonstrated its utility in quantifying the amount of exercise-induced aerobic training effect, the amount of heart muscle damage from a myocardial toxin, and the amount of diastolic dysfunction associated with chronic hypertension. Pharmacologic sympathetic stimulation and parasympathetic and beta adrenergic blockade demonstrate that the RSA amplitude is a sensitive indicator of autonomic function but also that approximately 25% of this reflex remains following both maximal stimulation and blockade. All in all, this 1- to 2-min resting test of this fundamental cardiopulmonary autonomic reflex has several current and many potential clinical uses. This is the first example of a simple test that employs second-order rhythm characteristics to assign relative risk. Its widespread adoption can in principle open the door to the full range of possibilities offered by the quantitative consideration of the time structure of rhythmic biological variability across the full range of relevant frequencies.