Heart rate variability

Heart disease in the last decade went top. Science does not stand still, every year there are new methods of diagnosis and treatment, which help fight diseases of different etiologies. Cardiology has always been considered one of the most important medical sciences. There is a constant "struggle" with cardio-vascular system diseases. The new methods of diagnosis and treatment appears in place of the long-known ones. A successful example is the analysis of ECG microalternations, which allows to predict the onset of cardiovascular disease. The heart is known to be a kind of stand-alone system, which has its own "power plant" - nodes that generate nerve impulses that cause the heart wall to contract. However, no matter how independent was the heart, the nervous system, both sympathetic and parasympathetic, affects it, and this can lead to malfunction of the heart. One of the modern methods of the evaluation of the heart and the nervous system interaction is to estimate heart rate variability (HRV).

What is the "Heart Rate Variability"

First, you must understand the term "variable" – it is a property of biological processes that are associated with the necessity of organism adaptation to changing environmental conditions. In other words, the variability is the mutability of different parameters, including heart rate, in response to exposure to some factors. Therefore, heart rate variability (HRV) reflects the cardiovascular system and the mechanisms of regulation of the whole organism. Scientists had discovered the relationship between the autonomous nervous system and death from cardiovascular disease, including sudden death.

Heart rate variability is the most convenient parameter by which you can evaluate the effectiveness of the interaction of the cardiovascular and other body systems. This analysis is becoming popular because due to its simplicity, also it is not invasive. This examination is beginning to be used in functional diagnosis actively, because the heart rate variability allows us to give an overall assessment of the patient's condition, as they reflected vital parameters of the body physiological functions control, these include the functional reserves of control mechanisms, and autonomic balance.

The influence of the sympathetic nerve increases heart rate by stimulating beta-adrenergic of sinus node. In turn the vagus stimulates cholinergic sinus node choline receptors, leading to bradycardia. The sympathetic system has a greater impact on the ventricles, while the vagus influences sinus and atrioventricular nodes.

Heart rate affect the phase of respiration. During inhalation vagal effect (influence of the vagus) is inhibited, and the heart beat rate is accelerated. During exhalation cardiac activity slows down because vagus is irritated. We can say that the heart rate is the reaction of the organism to the internal and external environmental stimuli. Consequently, the change of heart beating is a response to some factors changes, and is regulated by sympathetic and parasympathetic nervous system.

Cardiovascular system is a vivid example of the unique management system, which is based according to hierarchical principle, where each lower level is functioning autonomously in normal conditions. When there are changes in the environment and/or the development of pathological process in order to maintain homeostasis, the higher control levels are activated. The adaptation process requires the expenditure of information, energy and metabolic resources of the body. Resource management depends on the requirements presented to the organism by the environment, and is carried out through nervous, endocrine, and humoral mechanisms, which can be divided into autonomous and central. The intervention of the central control mechanisms into the functioning of the autonomous ones is performed only when the latter cease to function optimally.

Analysis of heart rate variability

The analysis of heart rate variability becomes more popular in cardiology research last years. It is based on the determination of RR intervals sequence of the electrocardiogram. Also NN-intervals (normal-to-normal) are mentioned, i.e. only the intervals between normal contractions.

Due to this analysis we can obtain information about the autonomic nervous system and number of reflex and humoral factors effect upon the heart.

Analysis of heart rate variability allows us to estimate the functional state of a person, also allows to monitor the dynamics and identify pathological conditions. It provides information about the body's adaptation reserve, allowing to predict the cardiovascular system failures.

Derating points to a violation of interaction of autonomic nervous and cardiovascular systems, and leads to the pathologies associated with the heart functioning. The highest parameters of heart rate variability are characteristic of healthy young people and athletes, since they have a higher parasympathetic tone. Various kinds of heart disease of organic nature results in low levels of variability and high sympathetic tone. The sharp decline is likely death.

Methods of heart rate variability assessment

Currently, there are several methods to assess heart rate variability. Among them there are three groups:

Statistical methods are based on measurement of NN-intervals and on a comparison of parameters. They quantify variability. The patient receives the cardiointervalogram after the examination. The cardiointervalogram is a set of RR-intervals that are displayed one after another.

For the analysis of cardiointervalogram the following criteria are used:

SDNN – the standard deviation of all NN-intervals. Shows the variability of periodic components of the recording, i.e. it is a summary parameter of HRV.

RMSSD – the square root of the mean squared difference of successive NNs.

pNN50 – the proportion of the number of pairs of successive NNs that differ by more than 50 ms divided by total number of NN intervals.

For HRV analysis geometric methods are also used. The essence is to get the law of cardio distribution as random variables. The distribution of cardio duration is displayed on the histogram.

SDNN – стандартное отклонение всех NN-интервалов. Отражает все периодические составляющие вариабельности за время записи, то есть является суммарным показателем ВСР.

RMSSD – данные оценки сравнения NN-интервалов.

pNN50 – данный критерий представляет отношение NN-интервалов, которые отличаются друг от друга более чем на 50 мсек, с общим числом NN-интервалов.

Для анализа ВСР используются также геометрические методы. Сущность заключается в получении закона распределения кардиоинтервалов как случайных величин. Распределение продолжительности кардиоинтервалов отображают на гистограмме.

In stress situations, also in pathological conditions the chart will have a narrow base and acute top (excessive). Asymmetric diagram observed in transient processes, violation of stationary process. Multimodal diagram shows no sinus rhythm (arrhythmia, atrial fibrillation).

Geometric methods allow to assess heart rate variability using the following parameters: mode, mode amplitude, and variation range.

Mode (Mo) - corresponds to the number RR-intervals, which are most often, therefore, it allows us to estimate the actual state of patient’s regulation systems.

Mode amplitude (AMo) - shows the proportion of intervals that correspond to the modal value. This parameter shows the stabilizing effect of the centralization of control heart rhythm.

Variation range (VAR) - corresponds to the difference between the length of the largest and the smallest intervals.

In order to assess the cardiovascular system degree of adaptation to the various factors and see the extent of regulation of these processes, extra parameters can be used and calculated. These include the index of vegetative balance (IVB), regulatory processes adequacy index (RPAI), tension index (TI) of the regulatory systems, vegetative rhythm index (VRI).

The index of vegetative balance indicates the ratio between the activity of sympathetic and parasympathetic parts of the autonomic nervous system. Regulatory processes adequacy index reflects the correspondence between the parasympathetic nervous system and leading level of sinus node. Vegetative rhythm index gives an indication of vegetative balance to assess the activity of the autonomous circuit regulation. Tension index of the regulatory systems reflects the degree of the influence of the central nervous system to the heart.

Autocorrelation analysis is used to assess the heart rate as a random process. The autocorrelation function is a diagram of the correlation coefficients dynamics obtained by sequential displacement of the analyzed time series by one in relation to its own row. It is a qualitative analysis showing the influence of the central nervous system upon the autonomic system of the heart.

Correlating rhythmography, or scatterography is a graphic presentation of cardio distribution (last and next) in the two-dimensional coordinate space. The value of R-Ri is placed on the abscissa axis, while the value of R-Ri+1 is on the ordinate axis. The diagram and region of points obtained by such a way (Poincare’s or Lorenz’s spots), is called the correlating rhythmogram or scatterogram. This method of HRV estimating relates to methods of nonlinear analysis, and is especially suitable for the detection and analysis of cardiac arrhythmias. The "cloud" is identified on the rhythmogram as an ellipse, which corresponds to the standard deviation of NN-intervals.

With this method, we can estimate the activity of the sympathetic autonomic nervous system to the heart. The scatterogram ellipse is extended along the bisector in healthy person.

The spectral analysis method of HRV

The use of spectral analysis allows to quantify the influence of different regulatory systems on the heart functioning.

There are three main spectral components that correspond to heart rate fluctuations of varying periodicity: high-frequency (HF), low frequency (LF) and very low frequency (VLF) components that are used in short-term ECG recording. The additional components of ultra-low frequency (ULF) are used for longer recordings.

HF component is associated with respiratory movements and shows the influence of the vagus nerve upon the heart functioning.

LF component characterizes the effect of sympathetic and parasympathetic nervous systems upon the heart rate.

VLF and ULF components demonstrate the effect of various factors, which include, for example, vascular tone, temperature regulation system, etc.

The important parameters are also TF - total power spectrum, the index of centralization IC (calculated by the formula (HF+LF)/VLF)), and the vagosympathetic interaction index LF/HF.

TF - allows us to estimate the total impact activity of autonomic nervous system upon the heart rhythm.
LF/HF - characterizes the balance of influence of parasympathetic and sympathetic nervous system upon the heart.

Heart rate variability in the project Ecg4me.com

The Ecg4me.com project offers for its clients the cardiovascular system performance monitoring, which is based on data Cardiovisor. Ecg4me.com service is equipped with one more type of survey that can be carried out using Cardiovisor – it is heart rate variability, which allows to estimate the adaptability of the organism and its functional reserves. The cardiovascular system can be evaluated by the degree of tension of regulatory systems, which is influences the heart rhythm.

After the examination the patient receives the statement, which is a plot of the "ladder of states", where he can see the approximate functional state of the regulatory systems.

Physiological norm – hence, the regulation of the heart by the autonomic nervous system is normal.

Psycho-emotional state, and the energy supply of the body are also in the normal range.

Prenosological state – a decrease in adaptive capacity is observed, there may be signs of fatigue.

Premorbid status - indicates overcharge of regulatory systems.

Failure to adapt - the autonomic nervous system is overcharged, the energy resources of the body are dramatically reduced. There are signs of cumulative fatigue and nervous strain in man. Patients are advised to visit the specialist. One of the main parameters will be IRSA, which allows comprehensive assessment of heart rate variability, and on this basis, the position of the patient on the ladder of states.
If the customer is registered as a "Private person", he also receives a visual cardiogram, the final conclusion and the numerical values of important parameters after the examination. Customers who are registered in the Ecg4me.com system as "Diagnostics cabinet ", get a detailed report on heart rate variability, which includes the spectral analysis of heart rate variability, pulsogramm, autocorrelation analysis, scatterogram. These data allow us to complete the picture and to assess the influence of each of the parts – the sympathetic, parasimathetic, humoral factors, –  upon the cardiovascular system.

Analysis of heart rate variability allows to assess the overall personal state, identify adaptive capabilities, analyze the psycho-emotional state. Heart rate variability can be used in medical therapy, also in sport medicine. Also it can be used in prenosological diagnostics.


View all articles