Do you know the basics of the heart rate variability?
The Heart Rate Variability (HRV) shows how adaptive an organism is. Thereby it represents a meaningful measure of health that can hardly be influenced. A variable heartbeat indicates a good state of health, while a constant heart rate is a warning sign. We can visualize these subtle differences from one heartbeat to the next one with the HRV measurement over 24 hours and can evaluate the state of health and vitality of a person very accurately – long before a disease occurs.
Dr.med. Alfred Lohninger
What is the Heart Rate Variability? How does a picture come from 100,000 data? Which factors influence the HRV?
The basics of HRV can be explained very detailed. Here is a brief overview of the most important facts to answer some frequently asked questions.
Already in the 3rd century AD the doctor Wang Shu-Ho (180-270) described: „If the heartbeat becomes as regular as the woodpecker’s knocking or the dripping of rain on the roof, the patient will die within four days.“ The clinical relevance of HRV was first described in 1963 by E.H. Hon and S.T. Lee. They noted that fetal stress precedes a change in heartbeat intervals even before changes in the heart rate itself occur. The Task Force realizes in its review of 1996 that HRV has great potential in assessing the role of the autonomic nervous system for healthy individuals as well as for patients with cardiovascular and noncardiovascular diseases (Parekh & Lee, 2005).
According to modern cardiology, the Heart Rate Variability is the most important prognosis parameter for cardiovascular and immune diseases and also allows a statement about the general regulatory capacity and health of the whole organism. People, whose heart rate variability is limited, will sooner or later develop statistically significant serious health disorders, such as heart disease, depression, neuropathy and even cancer. Improving heart rate variability through targeted lifestyle interventions allows all types of medication, including psychotropic drugs, to be saved because the adaptability of the whole organism is improved.
– Ärztemagazin (37/2004)
The heartbeat is controlled by the internal clock, respiration, emotions and external influences; which means, that the heart reacts directly to everything what a person experiences externally and thinks and feels inside with balanced changes (variations) of the heart beat sequences. Thus, the heart rate increases during physical exertion or stress and decreases at rest or during sleep.
This phenomenon is calld Heart Rate Variability, short HRV.
The HRV describes the ability of the heart to constantly change the time interval from one heartbeat to the next one and with that it can adapt to all changing challenges. It is a measure of the general adaptability of an organism. The control is done by activating the sympathetic (in the sense of tension) and the parasympathetic (in the sense of recovery) nerve. Responsible for accelerating or decelerating the heartbeat is the autonomic nervous system (Shaffer et al., 2014; McCraty & Shaffer, 2015). It is calculated from the millisecond intervals between the individual heart beats of a human being.
The more variable the heartbeat, the healthier the organism.
How is the HRV calculated?
An electrocardiogram records the time series of RR intervals (Gramann & Schandry, 2009). The RR interval is the time between two R-waves, which is the time span between the electrical stimulation (depolarization) of the heart chambers. These time series are then quantified in terms of their strength, time scale and inner patterns (for more information see „HRV-Praxis-Lehrbuch“ by Dr. Alfred Lohninger).
1,000 times a second it is looked for a R-wave. The distances between two nearby R-waves are measured in milliseconds (ms). The numerical values of these distances (around 120,000 per 24 hours) form the raw material of the data. The highly specialized software transforms data into numerical values and images.
Calculation of the heart rate:
1 minute = 60,000 milliseconds
There are several ranges that are used to analyze heart rate variability:
- time range (e.g. standard deviation of the RR intervals
- frequency range (e.g. spectrum of Heart Rate Variability)
Time phenomena and parameters of heart rate variability
The basis of the analysis in the time domain is the absolute interval duration between two R-waves or their deviation.
However, only the scattering amount by the average value of the interval duration (or its difference) within a given time range of a total derivative or within the total derivative (SDNN) is considered.
Based on the RR interval duration, the „span“ of the HRV can be determined (difference between minimum and maximum of the interval duration). The percentage distribution of the interval durations can be displayed in a histogram. The higher the value of the average RR interval, the lower the average heart rate. This may indicate an economic operation of the heart.
Another possibility of HRV analysis in the time domain is the representation of the determined values in the Poincaré or Lorentz plot (= scatter plot):
Established HRV time range parameters include minimum heart rate, maximum heart rate, total heartbeat in 24 hours, SDNN, SDANN, RMSSD or pNN50.
Frequency-related aspects and parameters of Heart Rate Variability
In 1981, Akselrod et al. presented spectral analysis for the quantitative assessment of cardiovascular beat-to-beat control. Fast Fourier Transformation (FFT) is used to convert.
The most important part of modern HRV diagnostics is the intuitive capture of the spectrogram as a graphic (Sammito et al., 2014; Task Force, 1996; Berntson et al., 1997).
The intensity of the HRV is expressed by the color coding and is demonstrated in milliseconds squared (ms²). A dense, high flaming, according to the power bar on the right edge of the picture, color-intense picture represents vitality. Based on the color spectrum of a gas flame it changes from light blue, medium blue, dark blue, dark red, light red, orange, yellow, white to gray. For example, light blue corresponds to the strongest intensity of at least 1,200 ms², red 240 ms² and gray 0 ms².
This results in the following frequency ranges:
- ULF (ultra low frequency): < 0,0033 Hz; can only be calculated in long-term variability measurements because of the cycle length. It reflects the daily rhythm and is largely robust towards behavioral effects.
- VLF (very low frequency): 0,04 – 0,0033 Hz; captures cycle lengths from 25 seconds to several minutes. Among other things, breathing patterns, thermoregulation, vasoactive substances, altitude and body position contribute to fluctuations in VLF.
- LF (low frequency): 0,04 – 0,15 Hz; detects vibrations in the range of about 10 seconds and accords with the periodic activity of the vasomotor part of the Baroreflex loop (Mayer wave activity)
- HF (high frequency): 0,15 – 0,40 Hz; includes oscillations in the range of 2 – 7 seconds. It shows the parasympathetic oscillation component of the respiratory sinus arrhythmia (RSA) and thus the respiratory synchronous heart rate fluctuation.
- TP (Total Frequency Power): 0 – 0,4 Hz; It is considered to be the amount of the influence of the vegetative on the cardiovascular system.