The low frequency band(LF) was previously called the “baroreceptor range” or “mid-frequency band” by many researchers, since it primarily reflects baroreceptor activity while at rest. This is consistent with the finding that lower HF power is associated with stress, panic, anxiety, or worry. In terms of psychological regulation, reduced vagally mediated HRV has been linked to reduced self regulatory capacity and cognitive functions that involve the executive centers of the prefrontal cortex. ![]() The mechanisms linking the variability of HR to respiration are complex and involve both central and reflex interactions. The high frequency band(HF) reflects parasympathetic or vagal activity and is frequently called the respiratory band because it corresponds to the HR variations related to the respiratory cycle known as respiratory sinus arrhythmia. The European Society of Cardiology and the North American Society of Pacing and Electrophysiology Task Force Report on HRV divided heart rhythm oscillations into 4 primary frequency bands high-frequency (HF): from 0.15 Hz to 0.4 Hz, low-frequency (LF): from 0.04 Hz to 0.15 Hz, very-low-frequency (VLF): from 0.0033 to0.04 Hz, and ultra-low-frequency (ULF): below 0.0033 Hz. During the time line of HRV science developments, major break through in understanding of the complex interacting mechanisms that operate HRV came after understanding HRV frequencies. HRV analysis is, beyond the scope of this editorial, but can be done with various analytical approaches, although the most commonly used are frequency domain (power spectral density) analysis and time domain analysis. Even in healthy subjects, the effects of cycle length dependence should be taken into account when assessing HRV. ![]() Elderly patients with ischemic heart disease or other pathologies develop less variability at increasingly lower HRs and ultimately lose the relationship between HR and variability, to the point that variability does not increase with reductions in HR. At lower HRs there is more time between heartbeats and variability naturally increases. As HR increases there is less time between heartbeats for variability to occur, thus HRV decreases. Higher HRs are independent markers of mortality in a wide spectrum of conditions. The average 24-hour HR in healthy people is approximately 73 bpm. Healthy, optimal function as we perceive it in 2017 is the result of continuous, dynamic, bi-directional interactions among multiple neural, hormonal, and mechanical control systems at both local and central levels. This in our perspective is complementary but not competitive to the great physiologist Walter Bradford Cannon who expand Claude Bernard concept of homeostasis and the steady state condition that body cells, tissues and organs are strived to maintain. The introduction of signal processing technologies that can acquire continuous time series data from physiological processes such as heart rate (HR), blood pressure (BP), and nerve activity, make it abundantly apparent that biological processes vary in complex and nonlinear ways, even during so called “steady-state” conditions. The importance of HRV as an index of the functional status of physiological control systems was noted only in 1965 when it was found that fetal distress is preceded by reductions in HRV before any changes occur in HR itself. The understanding of Heart rate variability, defined as the change in the time intervals between adjacent heartbeats, is an emergent property of interdependent regulatory systems that operates on different time scales to adapt to environmental and psychophysiological Challenges. There was no clear perception of the importance of variation between heart beats or frequency bands associated with it. ![]() The study of heart beat all over the time line of medicine from Galen and before to Ibn al-Nafis, and Ibn Sina passing to William Gilbert and his primitive attempts to record heart stimuli ending to Willem Einthoven who invented the modern ECG, was always concerned with the heart contraction. ![]() Since the dawn of human life, the innate perception of heart beat, being the source of life and the shine of the spirit that will depart only if the heart beating cease.
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