Chronobiology of the Cardiovascular System

**39**

**Chapter 4**

**Abstract**

Adolescents

Circadian Rhythm of Blood

*Anastasiia Ledyaeva, Sergey Klauchek and Mikhail Ledyaev*

Everything in our body is under control of central and peripheral pacemakers that regulate all the processes and functions according to the day-night and sleep-wake cycles. Cardiovascular system is not an exception. Blood pressure, heart rate, and even vascular resistance have circadian patterns. Nowadays new diagnostic devices provide all necessary data on 24-h variation of the hemodynamic parameters in patients of all ages. Due to the complex regulation mechanisms which underline this variation, circadian patterns are not the same in different people. Why do we need to assess these rhythms? First of all, it is a key to the early diagnosis of different cardiovascular diseases and their complications. When the circadian rhythm is impaired, for example, the level of blood pressure is within the normal ranges, but it does not decline at night or even is higher than at daytime, there is an increased risk of the development of arterial hypertension and target organ damage. There is a large amount of studies on 24-h rhythm of blood pressure in adults.

On the contrary, in children there is still a lack of data on this topic.

ambulatory blood pressure monitoring

**1. Introduction**

**Keywords:** circadian rhythm, blood pressure, adolescence, circadian index,

All physiological processes in the organism have a cyclic organization—from thermoregulation and activity of cardiovascular system (CVS) and respiratory systems to expression of genes, mitochondrial activity, and synthesis of proteins [1–3]. Endogenous rhythms in newborns are formed under the impact of exogenous synchronizers, such as light and sound. Circadian organization of excretion with urine of sodium and potassium occurs in a period from the 4th till the 20th week; on 2–3 weeks of the postnatal development, the synchronization of a body temperature with the day-night cycle takes place. At the present time, the active development of biomedical technologies allows to register and analyze the circadian variability of blood pressure (BP), heart rate (HR), and heart rate variability (HRV) by conducting their monitoring during 24 and more hours. The interest of scientists and clinical physicians to the diurnal variabilities of CVS parameters is also connected with the fact that based on the condition of the biological rhythms of a separate system of organs it is possible to judge the functional condition of an organism, the level of

Pressure in Children and
