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HEART RATE VARIABILITY IN 7 YEARS OLD CHILDREN
Akhmedova D.I.
1
, Popenkov A.V.
2
Republican Specialized Scientific and Practical Medical Center for Pediatrics of the
Ministry of Health of the Republic of Uzbekistan
1
,
Tashkent Pediatric Medical Institute
2
Abstract:
The article presents data on heart rate variability (HRV) in 7 years
old children. There are presented information of temporal, geometric, spectral
analysis of HRV as well as data of variation pulse oximetry. There is given a
comparative assessment of indicators depending on the gender and div mass index
of children. An analysis of the results of the study showed a strong direct and inverse
relationship between some of the indicators of HRV, as well as a difference in the
indicators of HRV in 7 years old children, depending on gender and div mass index.
Keywords:
7-year-old children, physical development, heart rate variability.
Heart rate variability (HRV) is the simplest and informative method of
assessing the status of the vegetative nervous system [5]. Also, HRV indicates the
adaptive capacity of the div and helps to identify the risk of unexpected death [1].
Most often, HRV is used in cardiology practice in determination of the adequacy of
therapy [4]. HRV is based on the determination of cardio intervals in the second
standard lead of electrocardiography. [2,3]. HRV assesses the physiological functions
of the div through the ratio of the activity of the different part of vegetative nervous
system [1], and allows to evaluate the functional capabilities of the div and carry
out preventive measures aimed at maintaining the health of the child [6]. For greater
reliability, the minimum recording should be at least 5 minutes. Also, orthostatic test,
Valsalva test are used for evaluation. To carry out these tests, it is necessary to adhere
to the stationarity condition. Studies should be conducted under the same conditions
and the length of the first and second records should be the same. Statistical data
processing methods are used to analyze heart rate variability. Statistical methods
based on the time difference between R-R intervals. These methods include HR
(heart rate), RRNN, mean RR interval duration, which evaluates the balance in the
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vegetative nervous system; SDNN is the square root of the cardio interval`s spread,
RMSSD and pNN50% are indicators that assess the state of the parasympathetic link
of the autonomic nervous system. Geometric methods are the least influenced by
artifacts, these include the triangular index and the St. George index, TINN reflect the
total HRV. In spectral analysis, the power is estimated depending on the oscillation
frequency. The frequency spectrum is usually divided into: high-frequency (0.2-0.4
Hz), low-frequency (0.04-0.15 Hz) and very low-frequency (0.003-0.04 Hz). Power
is measured in ms
2
. Measure the power contribution of the spectrum depending on
the frequency range. HF - high-frequency spectrum showing the activity of the
parasympathetic system, LF – indicates the activity of the sympathetic system, VLF –
reveals the activity of the suprasegmentally centers of the autonomic nervous system
[3].
Purpose of the study.
Determine the heart rate variability in 7 years old
children.
Materials and research methods.
The study involved 120 children. All
children underwent anthropometric measurements. There were selected only children
without acute and chronic diseases. The children were divided into 3 groups
depending on the div mass index. The first group consisted of 66 children with
BAZ (bmi for age) scores from -2 to +1 SDS; the second group included 29 children,
with a BAZ range of +1 to +2 SDS. The third group consisted of 25 children with
BAZ > +2 SDS. All children underwent ECG examination, cardiointervalography
with orthostatic test. The following indicators were used for analyses of HRV:
rrHRV, IQR, RRNN, HR, SDNN, RMSSD, pNN50%, TRI, ApEn, SD1, SD2,
SD1/SD2, VLF, LF, HF, IC, CV, Mo (the most common interval RR), SI (stress
index), RMI (respiratory modulation index), SAI (sympathoadrenal index), SWAI
(slow wave arrhythmia index), VPR (vegetative parasympathetic range), ARPI
(indicator of the adequacy of regulatory processes), VBI (vegetative balance index).
The statistical significance of the obtained measurements was determined by
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Student's t-test (t) with the calculation of the error probability (P). Significance level
p<0.05 was taken as statistically significant changes.
Results and discussions.
According to the results of the survey, correlations between
the indicators were revealed. An indicator >0.7 was taken as a strong correlation. A
strong direct correlation was found between: rrHRV - SDNN - RMSSD - pNN50% -
TRI - SD1/SD2 - CV - RMI. A strong inverse correlation was found between the
indicators: rrHRV and AMo (% of most common intervals RR), SI, SAI, SWAI,
ARPI, VPR. HR has a high inverse correlation with pNN50%, RMSSD, SDNN and a
high direct correlation with AMo, SI, SWI, ARPI. SI (stress index) and APRI (an
indicator of the activity of regulatory processes) have a strong inverse correlation
with rrHRV, SDNN, RMSSD, pNN50%, TRI. Correlation relationship between
statistical, spectral and geometric indicators with indicators of variation pulse
oximetry demonstrated in the table 1.
Table 1
Correlation relationship between statistical, spectral and geometric indicators
with indicators of variation pulse oximetry.
Indicators Mo
AMo SI
RMI SAI
SWAI ARPI VBI
rrHRV
0.50
-0.78 -0.75 0.71
-0.82 -0.65
-0.78
-0.74
RRNN
0.89
-0.59 -0.64 0.65
-0.63 -0.65
-0.73
-0.57
HR
-0.91 0.58
0.69
-0.61 0.65
0.64
0.75
0.61
SDNN
0.48
-0.73 -0.69 0.96
-0.77 -0.56
-0.7
-0.73
RMSSD
0.52
-0.68 -0.64 0.98
-0.75 -0.73
-0.67
-0.67
pNN50
0.61
-0.75 -0.69 0.90
-0.81 -0.79
-0.75
-0.70
TRI
0.48
-0.89 -0.67 0.78
-0.76 -0.50
-0.84
-0.71
SD1
0.52
-0.68 -0.64 0.98
-0.75 -0.73
-0.67
-0.67
SD2
0.43
-0.72 -0.71 0.90
-0.77 -0.42
-0.69
-0.75
SD1/SD2
0.53
-0.38 -0.42 0.73
-0.57 -0.99
-0.43
-0.4
LF%
-0.31 0.29
0.40
-0.58 0.52
0.70
0.32
0.41
HF%
0.31
-0.29 -0.40 0.58
-0.52 -0.70
-0.32
-0.41
LF/HF
-0.31 0.24
0.32
-0.47 0.44
0.63
0.29
0.32
VLF
-0.37 0.21
0.26
-0.54 0.35
0.64
0.26
0.26
LF
-0.17 0.18
0.24
-0.36 0.33
0.44
0.20
0.23
HF
0.25
-0.17 -0.23 0.40
-0.31 -0.36
-0.23
-0.24
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According to the indicators of anthropometric measurements, it was revealed
that the average height of boys is 131±7.4 сm., which corresponds to the 68th
percentile, and for girls - 128.34±6.4 cm (p<0.05), which corresponds to the 49th
percentile. The average weight of boys is 30.7±7.9 kg, and girls -29.10±6.5 kg
(p>0.05). The rrHRV indicator in boys was 7.66±2.7 c.u., and in girls it was 8.85±3.4
c.u. (p<0.05). The average heart rate in girls was slightly higher (89.13±12.1 bpm.)
than in boys (88.8±10 bpm), p>0.05. SDNN - an indicator reflecting the reserve
capacity of the div, was higher in girls (65.81±5.48 msec.) compared to boys
(54.88±3.51 msec.), p<0.05. Significant differences were also observed in RMSSD:
boys - 60.42±4.10 msec., girls - 76.61±7.48 msec. (p<0.05) and pNN50%: boys -
22.74±2.0%, girls - 29.24±3.56% (p<0.05). According to the indicators of the non-
linear evaluation method, a significant difference in the indicators was also
determined: TRI, ApEn, SD1, SD2. According to the spectral analysis data, the
power of the LF spectrum prevailed in boys, while the power of the HF spectrum
prevailed in girls (p<0.05).
Table 2
Anthropometric parameters and indicators of HRV in 7 years old children.
Index
Boys
Girls
Height, cm
131.13±0.82
128.34±1.02
Weight, kg
30.70±0.88
29.10±1.02
rrHRV* c.u.
7.66±0.31
8.85±0.55
IQR c.u.
6.56±0.27
7.14±0.36
RRNN, msec.
682.86±8.45
685.92±15.52
HR, bpm
88.80±1.10
89.13±1.91
SDNN, msec *
54.88±2.63
65.81±5.09
RMSSD, msec *
60.42±4.10
76.61±7.48
pNN50, % *
22.74±2.0
29.24±3.56
TRI c.u.*
2.97±0.11
3.37±0.21
ApEn c.u.*
0.83±0.01
0.78±0.02
SD1*
42.73±2.90
54.18±5.29
SD2*
63.64±2.057
74.28±5.19
SD1/SD2
0.65±0.02
0.69±0.03
LF, %
43.28±1.74
41.16±2.59
HF, %
56.72±1.74
58.84±2.59
LF/HF
0.94±0.08
0.85±0.11
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TP, ms2
1365.95
1302.23
VLF, ms2
531.71±22.52
476.25±33.53
LF, ms2 *
450.43±13.38
405.88±14.98
HF, ms2 *
383.82±10.89
420.10±18.0
IC
1.90±1.90
2.16±0.18
CV *
7.89±0.30
9.30±0.57
∆×
262.68±11.63
296.00±22.13
Mo, msec
669.76±8.0
664.00±11.71
Amo, msec
36.82±1.21
34.05±1.89
SI, c.u.
137.24±11.61
128.47±16.49
SAI, c.u.
1106.73±73.86
946.83±116.94
SWI, c.u. *
43.64±0.57
42.53±0.88
VPR, c.u.
6.86±0.57
6.61±0.57
ARPI, c.u.
56.35±2.34
53.30±3.61
Note * - p <0.05
According to the results of the temporal analysis of HRV, there were no
significant differences in heart rate in children both at rest and during the orthostatic
test. The lowest total indicator of HRV (SDNN - an indicator of restoration of div
reserves) both at rest and during the orthostatic test was observed in obese boys -
51.05±8.0 msec., and 41.69±5.46 msec., respectively. In girls, there were no
significant differences depending on the div mass index. This indicates a higher
reserve potential of the autonomic nervous system in girls compared to boys. In terms
of pNN50%, the 1st group had the highest rate: boys – 24.49±2.8%; girls - 32.32 ±
4.32%, while the lowest indicator was observed in children of the 3rd group: boys -
20.87 ± 5.2%, girls - 24.97 ± 7.8%, which indicates a high activity of the sympathetic
nervous system in obese children. In orthostatic test, the lowest indicators were
observed in children of the 2nd group: boys - 4.75 ± 1.52%, girls - 4.75 ± 1.11%.
Table 3
HRV indicators in 7 years old children at rest.
Index
1 group
(n=66)
2 group
(n=29)
3 group
(n=25)
Boys
(n=42)
Girls
(n=24)
Boys
(n=18)
Girls
(n=11)
Boys
(n=15)
Girls
(n=10)
HR,
bpm.
87.8±
1.3
88.2±
2.2
89.9±
1.5
89.1±
4.5
90.5±
3.98
90.8±
4.5
RRNN
688.9±
687.98±
670.14±
689.4±
679.62±
679.2±
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, msec. 10.3
17.4
11.57
35.11
29.5
38.2
SDNN,
msec.
56.6±
3.5
65.97±5.48 53.45±
3.49
67.74±
10.9
51.05±
8.07
63.78±
13.28
RMSS
D,
msec.
63.27±
5.63
77.29±8.23 55.4±
5.08
78.8±
16.95
57.66±
11.99
73.47±18.5
9
pNN50
, %
24.49±
2.80
32.32±
4.32
19.78±
2.78
28.08±8.
30
20.88±
5.3
24.98±
7.8
CV, % 7.9±
0.42
7.95±
0.48
8.55±
0.61
7.94±
0.89
6.89±
0.68
7.57±3216
0.94
Mo,
msec.
674.17±
9.67
667.37±15.
3
661.05±13.
11
668±
24.62
666.67±
26.95
654.54±
26.57
AMo,
%
35.14±
1.39*
33.89±
2.6
37.37±
1.91
31.5±
4.04
41.47±
4.19*
36.64±
4.02
VBI,
c.u.
173.29±
13.87*
146.48±27.
92
167.88±
19.78
155.03±
42.44
228.26±
48.32*
189.42±
34.03
ARPI,
c.u.
52.85±2.2
9*
52.41±4.87 57.06±
3.23
49.28±
7.63
66.63±
9.43*
58.49±
7.66
VPR,
c.u.
6.66±
0.45
6.07±
0.78
6.60±
0.59
6.57±
1.30
7.81±
1.20
7.58±
1.05
SI, c.u. 123.08±
10.34*
115.95±
24.39
129.11±
15.90
125.42±
37.03
192.81±49.
26*
152.87±28.
20
Note * - p <0.05
As can be seen from Table 3, the highest rates of AMo, VBI, ARPI are
observed in group 3 in children with obesity, and these rates are high in both boys
and girls. SI (an indicator reflecting the influence of the sympathetic department on
the autonomic nervous system): in boys of the 3rd group, with an orthostatic test, it
increases from 192.87 ± 49.2 c.u. up to 205.43±42.68 c.u., and for girls from
152.87±28.2 c.u. up to 208.98±48.3 c.u.
Table 4
HRV indicators in 7 years old children during orthostatic test.
Index
1 group
(n=66)
2 group
(n=29)
3 group
(n=25)
Boys
(n=42)
Girls
(n=24)
Boys
(n=18)
Girls
(n=11)
Boys
(n=15)
Girls
(n=10)
HR, bpm
103.0±
1.3
107.0±
2.6
105.0±
1.7
109.0±
4.65
104.0±
3.79
107.0±
4.66
RRNN, msec
582.87± 566.97± 571.98±
556.96±
584.72±
568.0±
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7.63
14.49
9.58
24.80
20.64
27.76
SDNN, msec
46.69±
2.82
45.82±
3.59
49.57±
4.04
44.22±
5.06
41.69±
5.46
44.7±
7.42
RMSSD, msec
32.11±
1.58
35.69±
3.47
32.62±
2.70
38.62±
7.53
31.95±
3.96
34.91±
6.17
pNN50, %
6.33±
1.01
8.08±
2.45
4.57±
1.11
4.75±
1.52
5.86±
2.10
8.54±
4.28
CV, %
7.90±
0.42
7.95±
0.48
8.55±
0.61
7.94±
0.89
6.89±
0.68
7.57±
0.94
Mo, msec
673.33±
14.32
648.42±
15.47
658.95±
14.46
644±
24.18
666.67±
26.67
654.55±
24.88
AMO, %
39.19±
1.18
36.32±
2.71
39.19±
1.18
39.90±
3.43
43.60±
3.24
41.18±
1.75
VBI, c.u.
173.29±
13.87*
168.41±
31.49
209.59±
48.99
165.11±
39.17
250.06±
43.99*
257.17±
55.97
ARPI, c.u.
44.51±
2.05*
46±
4.02
48.15±
2.57
42.90±
6.25
56.73±
7.17*
52.05±
6.61
VPR, c.u.
8.78±
0.63
8.43±
0.96
9.88±
2.11
9.46±
1.72
10.78±
1.60
11.34±
2.03
SI, c.u.
132.82±
11.50*
134.44±
27
166.78±
44.15
132.95±
33.67
205.43±
42.68*
208.98±
48.38
Note * - p <0.01
Conclusions.
According to the results of the study, it can be concluded that
there is a strong correlation between the indicators of heart rate variability, so there is
no need to apply all methods of assessment. There is a high significance of
differences between indicators in boys and girls. According to spectral analysis and
statistical analysis, the parasympathetic division of the nervous system predominates
in girls. However, when assessed according to the indicators proposed by R.M.
Baevsky [7,8], (stress index), hypersympathicotonia is noted in both girls and boys.
Based on this, it can be assumed that children aged 7 years are characterized by a
higher stress index than adolescents and adults. This period is critical for children,
and during the first year of education, children adapt to new environmental
conditions. There is a correlation between the excessive influence of the central and
sympathetic nervous systems on obese children, which is reflected in the indicators of
ARPI and SI during the orthostatic test.
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