Autonomic tone, measures

Measures of autonomic tone Exercise testing Biochemical markers... 

Heart rate variability (HRV), heart rate turbulence (HRT), and baroreceptor reflex sensitivity (BRS) comprise the three currently used measures of autonomic tone. Autonomic tone is implicated in the pathogenesis of VT/VF, mainly as a result of enhanced sympathetic tone and diminished parasympathetic tone (64). Thus, analysis of autonomic tone may correlate with arrhythmic events or total mortality. 

HRV assesses the modulation of autonomic tone on the sinus node, or simply put, the irregularity of sinus rhythm. Methods of measuring HRV fall under broad categories of being either time domain or frequency domain analyses. Time domain measurements involve statistical analyses of the variability in the R-R interval, while frequency domain measurements use spectral analysis of a series of R-R intervals to classify HRV into ultra-low frequency, very low frequency, low frequency, high frequency, and total power. One method is not better than another as there is no gold standard (65). 

Having sermonized so long and hard about the time dimension, I am embarrassed now to promote a model that practically ignores it Time was the second dimension in activation-only models that plotted functions like EEG synchronization, desynchronization, muscle tone, eye movement, and autonomic measures as the first dimension. In the still traditional sleep charts, these functions rise and fall against time. In the three-dimensional model I will now develop, time is a fourth dimension, seen only as a sequence of points within the state space. 

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