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METHODS BASED ON THE STATISTICAL TRANSFORMATIONS
Statistical methods are used to quantify HRV in the studied period of time. When using them, a cardiointervalogram is considered as a set of consecutive time intervals (numerical values of the duration of R – R intervals).
Key indicators of statistical analysis:
Hsr. (Mathematical expectation, M, Меan, RRNN) - the average value of all R – R intervals in the sample. Fully correlates with heart rate.
Increase - probably reflects the predominance of the tone of the PSNS and indicates the high functionality of the CVS.
Decrease - characterizes the activation of higher levels of regulation of the heart rhythm, which happens during physical exertion, during stress or CVS diseases.
The average value in healthy adults: men - 0.94 ± 0.03 sec, women - 0.77 ± 0.06 sec.
Max is the value of the longest RR interval. In the absence of rhythm disturbances,
conduction and recording artifacts reflects PSNS activity.
Min is the value of the shortest RR interval. In the absence of rhythm and conduction disturbances and recording artifacts, it reflects the activity of sympathetic regulation of SR.
Confidence interval - a value that shows the confidence limits of the arithmetic average, beyond which there is little chance. Depends on the error of representativeness, standard deviation and the number of analyzed cardio intervals.
Dispersion is the average of the deviations of the individual values of the attribute squared from the average value, i.e., it is the square of the mean square deviation. Reflects the total power of all periodic and non-periodic oscillations. Dispersion during exercise in healthy people remains unchanged or decreases slightly. In diseases of the cardiovascular system, the variance either decreases significantly, or, much less often, paradoxically increases.
The average value in healthy people: 0.006 ± 0.00086.
Heart rate (heart rate) - reflects the total effect of heart rate regulation. Fully correlates with RRNN.
Increase - means the mobilization of CVS to ensure work in adverse conditions (physical activity, stress, illness), which indicates an increase in the tone of the SNS.
Decrease - indicates an increase in the tone of PSNS.
Average in healthy adults: 60–90 strokes per minute.
? (“sigma” is read) - the standard deviation (standard deviation of all R – R intervals, standard deviation, SDNN, CLV, SDRR) is an integral indicator that reflects the total effect of the sympathetic and parasympathetic divisions of the ANS on the sinus node.
Increase - indicates a shift in vegetative equilibrium in the direction of the prevalence of PSNS. Decrease - indicates a shift in autonomic equilibrium towards the predominance of the SNA. The average value in healthy people under 25 years old: 70 ± 10 ms; 26-40 years: men - 60 ± 6 ms., Women - 60 ± 5 ms; older than 40 years: men - 60 ± 8 ms, women - 50 ± 4 ms.
As (asymmetry coefficient) - reflects the degree of stationarity of the studied time series, as well as the presence and severity of transients.
Ex (excess) - reflects the speed (steepness) of the change of random non-stationary components of the time series and to a greater extent characterizes local non-stationary.
V (CV, coefficient of variation) - in physiological sense, does not differ from the mean square deviation, but is normalized in terms of heart rate. It is calculated by the ratio? / Hsr. x 100%.
The average value in healthy people under 25 years old: men - 7.1 ± 1.1%, women - 7 ± 0.4%; 26–40 years old:
men - 5.6 ± 0.5%, women - 6.1 ± 0.4%; over 40 years: men - 6.4 ± 0.7%, women - 6.1 ± 0.4%.
In general, statistical indicators quite fully characterize the formation of CI under the influence of random factors. However, unlike the spectral analysis indicators, they do not reflect the internal structure of the CI series and do not allow one to judge the mechanisms that provide the observed final effect of regulatory influences.
TIME ANALYSIS Synonym: (Time Domain).
Temporal analysis refers to a group of methods based on the use of statistical calculations. The method differs from statistical analysis not in the mechanism of parameter calculation, but in the presence of specific indicators that are used only for the analysis of HRV.
The main advantages of temporary analysis are:
• high prognostic value of the method;
• relatively high reproducibility of indicators;
• the possibility of increasing the reliability of the results with an increase in the number of analyzed CI.
An increase in the values of all indicators of the temporary analysis corresponds to an increase in the influence of PSNS.
The decrease corresponds to the increased influence of the SNA and higher centers of regulation of SR.
Temporal analysis metrics used to analyze records of any length:
RRNN (Mathematical expectation, M, Меan, Хср.) - average value of all R – R intervals in the sample. Reflects the activity of the SNS and humoral mechanisms of regulation of CP. Fully correlates with heart rate.
The average value in healthy people of 18 years in the analysis of short sections of HRV: men: 940 ± 30
ms, women - 770 ± 60 ms.
The average value in healthy people in the analysis of long records: 760 ± 96 ms.
SDNN is the mean square deviation (standard deviation of all R – R intervals,?, Standard deviation, CLV, SDRR) is an integral indicator, mainly reflecting the total effect of the sympathetic and parasympathetic divisions of the ANS on the SC.
It characterizes HRV as a whole.
The average value in healthy people under 25 years old when analyzing short sections of HRV: 70 ± 10 ms; 26–40 years: men - 60 ± 6 ms, women - 60 ± 5 ms; older than 40 years: men - 60 ± 8 ms, women - 50 ± 4 ms.
The average value in healthy people in the analysis of long records: 141 ± 39 ms.
rMSSD (the square root of the sum of the differences of consecutive R – R intervals) is an analogue of the SDNN indicator. Reflects the ability of SU to concentrate heart rate.
The average value in healthy people under 25 years in the analysis of short sections of HRV: 49.93 ± 15.23 ms.
The average value in healthy people in the analysis of long recordings: 27 ± 12 ms.
NN50 count - the absolute number of adjacent intervals, differing by more than 50 ms. Such differences in neighboring cardiac intervals are due to the appearance of pauses and increased heart rate, they are amplified with a predominance of PSNS. The value of the indicator usually increases with increasing recording time.
PNN50 - percentage of episodes of difference in consecutive intervals of more than 50 ms. The value of the indicator does not depend on the recording time, therefore it is used more often than the indicator NN50 count.
The average value in healthy people under 25 years in the analysis of short sections of HRV: 29.4 ± 19.55%.
The average value in healthy people when analyzing long-term records: 18 ± 13%.
Temporary analysis metrics used only to analyze long recordings:
SDNN Index (SDNNi) is the average of the standard deviations of NN intervals calculated over 5-minute intervals throughout the recording.
The average value in healthy people: 54 ± 15 ms.
SDANN is the standard deviation of the average values of NN intervals calculated over 5-minute intervals throughout the recording. In general, corresponds to the SDNN indicator. It has high prognostic significance.
The average value in healthy people: 127 ± 35 ms.
SDSD is the standard deviation of the differences between adjacent NN intervals.
The differential index is the difference between the values of the slices of the differential histogram measured at certain levels (for example, at the level of 1000 and 10000 CI) .
The logarithmic index is the coefficient of the exponential curve, which is the best approximation of the differential histogram .
The average daily parameters of the temporary analysis of HRV in healthy individuals 20-99 years old 
ANALYSIS OF SHORT SITES OF THE RHYTHMOGRAM BY G.V. RYABYKINA
At the Research Institute of Cardiology named after Myasnikov, a group of employees led by G. V. Ryabykina in the 90s developed an original method for the analysis of HRV [95-96], consisting of the following steps:
1. Dividing the rhythmogram into successive sections of 33 KI.
2. Calculations of the absolute value of the sum of the differences between the values of subsequent and previous cardio-intervals in each analyzed section (an indicator of the variability of a short section of the rhythmogram - SRS).
3. Statistical analysis of the data obtained for all sections of the rhythmogram.
The advantages of the method are:
• The ability to analyze the rhythmogram if the initial ECG is very noisy (for example, frequent rhythm or conduction disturbances, the presence of artifacts) and the absence of the need to isolate stationary sections of the rhythmogram, as in spectral analysis.
• The ability to correct and interpret HRV values depending on heart rate, gender, age and time of day.
Values of SRS normally fluctuate over a wide range, depending on the time of day, heart rate and age of the subject.
For each patient, the SRS values are compared with the thresholds of low variability, determined by the value below which the SRS value in practically healthy people occurs only in 1-2% of cases.
The frequency of detecting SRS values below the selected threshold is determined - the percentage of small variability (PMV). In patients with heart failure, the PMV value gradually increases with the transition from I to IV FC.
The percentage of sites with low variability (PMV) in the groups of healthy individuals and patients with different functional classes of heart failure (according to G.V. Ryabykina)
An informative indicator is also the indicator m (VCRM), which is calculated as the average SRS of all recording sections and characterizes the total variability of the SR.
The lower thresholds of the norm of the values of the VKRM
Variability of SR should be considered normal if the value of the SRS is higher than the upper threshold corresponding to the time of day. A slight decrease corresponds to the value of the SCRS, which is in the range between the upper and lower threshold. In the event that the SCRS is less than the lower threshold, we can talk about a significant reduction in HRV.
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