**2. Circadian rhythms of peripheral (brachial) and central (aortic) blood pressure in adolescents**

The main problem in pediatrics is that new approaches that are developed in medical diagnostics are firstly probated in adults, and it takes sometimes years before they will be approved for usage in children. The ambulatory blood pressure monitoring is not the exception. There are several studies that make a fundament for the guidelines and show the important role of that method in early diagnostic of arterial hypertension (AH) in young population, but it seems that the normal ranges of some chronobiological parameters were taken from adults' guidelines without any changes. But we have to keep in mind that adolescents could have some peculiarities of circadian organization of different biological parameters due to changes in hormonal regulation that follow the puberty. This hypothesis is based also on the data published by some authors. For example, it seems interesting why overdipping pattern for DBP is so common and is not so for SBP.

Due to a lack of data on peculiarities of circadian patterns in adolescents, we performed a study in 354 healthy children from 12 to 17 years old. The average nocturnal BP decline did not differ in boys and girls (*p* > 0.05). Average CI for brachial systolic BP was 12.2%; for brachial diastolic BP, 18.3%; and for brachial mean BP, 15.5%. Average CI for aortic systolic BP was 12%; for aortic diastolic BP, 19.5%; and for aortic mean BP, 16%.

Then we looked at the distribution of different circadian BP profiles in the studied group. The majority (71.8%) of adolescents were "dippers" for SBP, 26.5% were "non-dippers" for SBP, and the minority (1.7%) of adolescents were "overdippers" for SBP (**Figure 1**). In the case of DPB, there were different results: 50.3% "dippers," 10.5% "non-dippers," and 39.3% "overdippers" (**Figure 2**).

The results of descriptive statistics of CI of brachial BP are shown in **Table 1** (girls) and **Table 2** (boys). Our findings supported the hypothesis that the normal ranges for CI in children differ from ranges for adults. The data from percentile rank could be interpreted in the following way: 25–75 percentile is the normal range, 5–25 percentile shows the values of the parameter that are lower than normal, 75–95 percentile is the values that are higher than normal, and <5 percentile and >95% provide the lowest and the highest values that in clinical practice describe the pathological change in the parameter. The normal range for CI of SBP in adolescents

**Figure 1.** *The distribution of different circadian SBP profiles in the studied group.*

#### *Chronobiology - The Science of Biological Time Structure*

**Figure 2.**

*The distribution of different circadian DBP profiles in the studied group.*

**Table 1.**

*Descriptive statistics of circadian index of brachial BP and its percentile distribution in adolescent girls.*

#### **Table 2.**

*Descriptive statistics of circadian index and its percentile distribution in adolescent boys.*

is 9–15%, for CI of DBP is 14–23%, and for CI of MBP is 12–20%. Thereby for DBP the nocturnal dipping has a greater extend in physiological conditions in comparison with the SBP. This supported by statistical analysis that showed the significant differences in average values 12.1% (CI SBP) versus 18.2 (CI DBP) (*p* < 0.05) in adolescents of both sexes. As shown above, we talk about impaired circadian BP profile in adults using the same normal ranges for SBP and DBP<10% and higher than 20% of nocturnal decline of BP. But in children we found different values: the impaired SBP circadian profile is <5% and higher than 19%, DBP profile <6 and >28%, and MBP profile <6 and >24%. So, one can see that the profile "overdipping" for DBP starts from higher values in children in comparison with adults.

There was similar data for CI of aortic BP (**Table 3** for girls, **Table 4** for boys). Aortic DBP decrease to the greater extend at night in comparison with aortic SBP and MBP (*p* < 0.05).

In adolescents with dipping daily profile of SBP and DBP (a nocturnal decrease from 10 to 20%), the relative power of LF% during day was 35.1 ± 1.1%, LF% at night was 27.1 ± 1.8%, HF% during day was 28.3 ± 2.1%, HF% at night was 35.2 ± 1.9%, and circadian index of LF/HF was 1.3 ± 0.007, showing the physiological daily rhythm of fluctuations in the ratio between sympathetic and parasympathetic regulation contour.

**43**

**Table 4.**

**Table 3.**

*Circadian Rhythm of Blood Pressure in Children and Adolescents*

35.1 ± 1.1% for LF%; 33.7 ± 1.1 vs. 27.2 ± 2.1% for VLF%, *p* < 0.05).

In adolescents the degree of nighttime decline in the SBP exceeded 20%, the relative power of LF% during wakefulness was significantly higher than in adolescents with a normal decrease in the SBP at night (41.2 ± 1.7 vs. 35.1 ± 1, 1%, respectively, *p* < 0.05), and the circadian index of LF/HF was 1.5 ± 0.006. In adolescents with an excessive decrease in DBP, the circadian index LF/HF was 1.7 ± 0.006, and the relative power of LF and VLF% during the day was significantly higher in comparison with adolescents with a normal decrease in DBP (42.6 ± 2.1% against

In adolescents with insufficient nighttime decreases in SBP and/or DBP (<10%), the circadian index LF/HF was 1.1 ± 0.007, which indicates a relative absence of a change in the ratio of the parasympathetic and sympathetic regulations at night and, as a result, smaller amplitude of the circadian rhythm of the activity of the autonomic nervous system. The average values of the relative power of LF and HF% in the group with an insufficient decrease in SBP and/or DBP during wakefulness did not significantly differ from the group with normal nocturnal decline in BP (*p* > 0.05). The main characteristic of this group of adolescents was the absence of a significant decrease in the relative power of LF% at night (37.1 ± 2.1% during the

Puberty is a difficult critical period of the development, and every age in that period has its peculiarities. We performed ANOVA with post hoc Bonferroni test to find out if there are any differences in CI of CBP, DBP, and MBP in three age subgroups: 12–13, 14–15, and 16–17 years. The results are shown in **Table 5** (for brachial BP in boys), **Table 6** (for brachial BP in girls), **Table 7** (for aortic BP in boys), and **Table 8** (for aortic BP in girls). In boys there was a significant difference in the value of CI SBP and CI DBP between boys of different age subgroups (*p* < 0.05). That was supported by the results of Pearson correlation analysis between the CI and age, but the link is weak, so even if it is significant (*p* < 0.05), the hypothesis that the value of CI decreases with age has to be approved in the future studies. In girls, there were neither significant difference in the value of CI between age subgroups nor a significant correlation between CI and age (*p* > 0.05). We suppose that this can be explained by the different times of the puberty onset in boys and girls. As we know,

**Parameter Mean Minimum Median Maximum Percentile**

*Descriptive statistics of circadian index of aortic BP and its percentile distribution in adolescent girls.*

*Descriptive statistics of circadian index of aortic BP and its percentile distribution in adolescent boys.*

**Parameter Mean Minimum Median Maximum Percentile**

CI SBP (%) 12 0 11 24 5 8 15 19 CI DBP (%) 19 3 19 34 6 14 24 30 CI MBP (%) 16 3 16 28 6 12 19 24

CI SBP (%) 12 1 12 25 4 8 16 20 CI DBP (%) 20 3 21 42 8 15 25 31 CI MBP (%) 16 2 17 34 7 13 20 25

**5 25 75 95**

**5 25 75 95**

*DOI: http://dx.doi.org/10.5772/intechopen.87112*

day vs. 32.2 ± 1.9% at night).

#### *Circadian Rhythm of Blood Pressure in Children and Adolescents DOI: http://dx.doi.org/10.5772/intechopen.87112*

In adolescents the degree of nighttime decline in the SBP exceeded 20%, the relative power of LF% during wakefulness was significantly higher than in adolescents with a normal decrease in the SBP at night (41.2 ± 1.7 vs. 35.1 ± 1, 1%, respectively, *p* < 0.05), and the circadian index of LF/HF was 1.5 ± 0.006. In adolescents with an excessive decrease in DBP, the circadian index LF/HF was 1.7 ± 0.006, and the relative power of LF and VLF% during the day was significantly higher in comparison with adolescents with a normal decrease in DBP (42.6 ± 2.1% against 35.1 ± 1.1% for LF%; 33.7 ± 1.1 vs. 27.2 ± 2.1% for VLF%, *p* < 0.05).

In adolescents with insufficient nighttime decreases in SBP and/or DBP (<10%), the circadian index LF/HF was 1.1 ± 0.007, which indicates a relative absence of a change in the ratio of the parasympathetic and sympathetic regulations at night and, as a result, smaller amplitude of the circadian rhythm of the activity of the autonomic nervous system. The average values of the relative power of LF and HF% in the group with an insufficient decrease in SBP and/or DBP during wakefulness did not significantly differ from the group with normal nocturnal decline in BP (*p* > 0.05). The main characteristic of this group of adolescents was the absence of a significant decrease in the relative power of LF% at night (37.1 ± 2.1% during the day vs. 32.2 ± 1.9% at night).

Puberty is a difficult critical period of the development, and every age in that period has its peculiarities. We performed ANOVA with post hoc Bonferroni test to find out if there are any differences in CI of CBP, DBP, and MBP in three age subgroups: 12–13, 14–15, and 16–17 years. The results are shown in **Table 5** (for brachial BP in boys), **Table 6** (for brachial BP in girls), **Table 7** (for aortic BP in boys), and **Table 8** (for aortic BP in girls). In boys there was a significant difference in the value of CI SBP and CI DBP between boys of different age subgroups (*p* < 0.05). That was supported by the results of Pearson correlation analysis between the CI and age, but the link is weak, so even if it is significant (*p* < 0.05), the hypothesis that the value of CI decreases with age has to be approved in the future studies. In girls, there were neither significant difference in the value of CI between age subgroups nor a significant correlation between CI and age (*p* > 0.05). We suppose that this can be explained by the different times of the puberty onset in boys and girls. As we know,

**Table 3.**

*Chronobiology - The Science of Biological Time Structure*

*The distribution of different circadian DBP profiles in the studied group.*

is 9–15%, for CI of DBP is 14–23%, and for CI of MBP is 12–20%. Thereby for DBP the nocturnal dipping has a greater extend in physiological conditions in comparison with the SBP. This supported by statistical analysis that showed the significant differences in average values 12.1% (CI SBP) versus 18.2 (CI DBP) (*p* < 0.05) in adolescents of both sexes. As shown above, we talk about impaired circadian BP profile in adults using the same normal ranges for SBP and DBP<10% and higher than 20% of nocturnal decline of BP. But in children we found different values: the impaired SBP circadian profile is <5% and higher than 19%, DBP profile <6 and >28%, and MBP profile <6 and >24%. So, one can see that the profile "overdipping"

**Parameter Mean Minimum Median Maximum Percentile**

*Descriptive statistics of circadian index of brachial BP and its percentile distribution in adolescent girls.*

**Parameter Mean Minimum Median Maximum Percentile**

CI SBP (%) 12.1 0 12 26 5 9 15 19 CI DBP (%) 18.2 1 18.5 33 6.3 14 23 28 CI MBP (%) 15.8 2 16 28 6 12 19.5 24

CI SBP (%) 12.14 1 12 24 5 9 15 19 CI DBP (%) 18.29 2 18 34 7 14 23 29 CI MBP (%) 15.19 3 15 38 6 12 19 24

**5 25 75 95**

**5 25 75 95**

There was similar data for CI of aortic BP (**Table 3** for girls, **Table 4** for boys). Aortic DBP decrease to the greater extend at night in comparison with aortic SBP

In adolescents with dipping daily profile of SBP and DBP (a nocturnal decrease

from 10 to 20%), the relative power of LF% during day was 35.1 ± 1.1%, LF% at night was 27.1 ± 1.8%, HF% during day was 28.3 ± 2.1%, HF% at night was 35.2 ± 1.9%, and circadian index of LF/HF was 1.3 ± 0.007, showing the physiological daily rhythm of fluctuations in the ratio between sympathetic and parasympa-

for DBP starts from higher values in children in comparison with adults.

*Descriptive statistics of circadian index and its percentile distribution in adolescent boys.*

**42**

**Table 2.**

**Table 1.**

**Figure 2.**

and MBP (*p* < 0.05).

thetic regulation contour.

*Descriptive statistics of circadian index of aortic BP and its percentile distribution in adolescent girls.*

**Table 4.**

*Descriptive statistics of circadian index of aortic BP and its percentile distribution in adolescent boys.*

the main hormonal changes in girls start earlier, so by the age of 12–13, they have higher stage of puberty in comparison with boys. It is necessary to provide the same study in younger children. The main limitation of our study was that the adolescents in different age subgroups are not the same, so it was not the same boy or girl who was growing up from 12 to 17 years old. Thus, we cannot rule out other individual peculiarities of adolescent organism that could affect the results.

#### **Table 5.**

*Value of circadian index of brachial BP in age subgroups of adolescent boys.*

#### **Table 6.**

*Value of circadian index of brachial BP in age subgroups of adolescent girls.*

**45**

*Circadian Rhythm of Blood Pressure in Children and Adolescents*

**(***n* **= 52)**

*Value of circadian index of aortic BP in age subgroups of adolescent girls.*

Analysis of the circadian rhythm of the peripheral and central blood pressure revealed gender-related features of the diurnal SBP and DBP profiles—the decrease of the degree of nocturnal decline in brachial and aortic pressure with age in healthy boys and the absence of such changes in girls 12–17 years old. The tendency to decrease with age of the degree of nocturnal dip in peripheral pressure in young men indicates the peculiarities of the age dynamics of the formation of the circadian organization of the vegetative mechanisms of regulation of the vascular wall stiffness that underlie the formation of daily arterial pressure profile. The circadian rhythm of brachial and aortic diastolic pressure in adolescents was characterized by a shift of the 25–75 percentile ranges toward higher levels of the degree of nocturnal dip in DBP compared to that for the SBP (14–23 and 9–15%, respectively). This could be probably due to the different contribution of the vasomotor component to the formation of circadian fluctuations of systolic and diastolic pressures. In addition, the values of 95 percentile, by which the disturbance of the arterial blood pressure profile is pronounced, were 28–29% for brachial and aortic diastolic pressures, which exceeds the generally accepted standard values for the adult population (22%). Thus it is necessary to provide more studies on mechanisms that underline the differences. The obtained data can be used to improve accuracy when decoding

**14–15 years old (***n* **= 74)**

CI SBP (%) 12 ± 0.6 11 ± 0.5 11 ± 0.8 *p* > 0.05 CI DBP (%) 21 ± 0.8 19 ± 0.8 19 ± 1.0 *p* > 0.05 CI MBP (%) 17.5 ± 0.8 17.4 ± 0.7 18.1 ± 0.8 *p* > 0.05

**16–17 years old (***n* **= 58)**

−0.04 *p* > 0.05

−0.1 *p* > 0.05

−0.03 *p* > 0.05

*p***-value**

data of ABPM and interpretation of the results obtained in adolescents.

The authors declare no conflict of interest.

*DOI: http://dx.doi.org/10.5772/intechopen.87112*

**Parameter 12–13 years old**

**3. Conclusion**

r Pearson (age/CI

r Pearson (age/CI

r Pearson (age/CI

SBP)

DBP)

MBP)

**Table 8.**

**Conflict of interest**

**Table 7.**

*Value of circadian index of aortic BP in age subgroups of adolescent boys.*

*Circadian Rhythm of Blood Pressure in Children and Adolescents DOI: http://dx.doi.org/10.5772/intechopen.87112*

#### **Table 8.**

*Chronobiology - The Science of Biological Time Structure*

**Parameter 12–13 years old**

**Parameter 12–13 years old**

**Parameter 12–13 years old**

the main hormonal changes in girls start earlier, so by the age of 12–13, they have higher stage of puberty in comparison with boys. It is necessary to provide the same study in younger children. The main limitation of our study was that the adolescents in different age subgroups are not the same, so it was not the same boy or girl who was growing up from 12 to 17 years old. Thus, we cannot rule out other individual

> **14–15 years old (***n* **= 68)**

**14–15 years old (***n* **= 74)**

**14–15 years old (***n* **= 68)**

CI SBP (%) 13 ± 0.8 11 ± 0.5 10 ± 0.5 *p* < 0.05 CI DBP (%) 21 ± 1.0 19 ± 0.8 17 ± 0.8 *p* < 0.05 CI MBP (%) 18.3 ± 0.8 16.6 ± 0.7 15.6 ± 0.9 *p* = 0.08

CI SBP (%) 13 ± 0.6 12 ± 0.5 12 ± 0.7 *p* > 0.05 CI DBP (%) 21 ± 0.9 18 ± 0.8 19 ± 1.0 *p* > 0.05 CI MBP (%) 16.8 ± 0.7 15.5 ± 0.6 15.4 ± 0.9 *p* > 0.05

CI SBP (%) 13 ± 0.6 12 ± 0.5 11 ± 0.5 *p* < 0.05 CI DBP (%) 19 ± 0.9 18 ± 0.8 17 ± 0.8 *p* < 0.05 CI MBP (%) 15.9 ± 1.0 14.0 ± 0.7 15.8 ± 0.7 *p* > 0.05 r Pearson (age/CI SBP) −0.2 *p* < 0.05 r Pearson (age/CI DBP) −0.2 *p* < 0.05 r Pearson (age/CI MBP) −0.1 *p* > 0.05

**16–17 years old (***n* **= 56)**

**16–17 years old (***n* **= 58)**

−0.01 *p* > 0.05

−0.1 *p* > 0.05

−0.1 *p* > 0.05

**16–17 years old (***n* **= 56)**

−0.2 *p* < 0.05

−0.2 *p* < 0.05

−0.2 *p* > 0.05

*p***-value**

*p***-value**

*p***-value**

peculiarities of adolescent organism that could affect the results.

**(***n* **= 46)**

*Value of circadian index of brachial BP in age subgroups of adolescent boys.*

**(***n* **= 52)**

*Value of circadian index of brachial BP in age subgroups of adolescent girls.*

**(***n* **= 46)**

*Value of circadian index of aortic BP in age subgroups of adolescent boys.*

**44**

**Table 5.**

r Pearson (age/CI

r Pearson (age/CI

r Pearson (age/CI

r Pearson (age/CI

r Pearson (age/CI

r Pearson (age/CI

SBP)

DBP)

MBP)

**Table 7.**

SBP)

DBP)

MBP)

**Table 6.**

*Value of circadian index of aortic BP in age subgroups of adolescent girls.*