The relatively high pulse rate in early childhood and primary school age is due to the early development of the sympathetic innervation of the heart. Vagal tone appears after 3 years. It increases with age, especially in the physical development of children. Basically, the development of the innervation of the heart is completed by 7-8 years. At 7-9 years of age and older there is respiratory arrhythmia of the heart at rest and while sitting. Inhalation pulse quickens and slows down during exhalation. This arrhythmia is reduced to 13-15 years, it increased again in 16-18 years, and then gradually disappear.
Children 1 kg of minute volume is relatively large, due to a large growing body metabolism. The value of cardiac output in children depends more on heart rate than from an increase in systolic volume.
Pressor and depressor reflexes cause children more easily and more frequently than in adults. In early childhood, relatively high pulse pressure (50-60 mm Hg. V.), And total blood pressure varies individually. It is somewhat lower than in adults, and comes up to the standards of the adult puberty. Some older students observed a temporary ‘youthful hypertension “(up to 140 mm Hg. Art.). The speed of blood circulation in children than in adults (3 years – 15 in 14 – 18.5 s). One of the reasons etoyu – shorter length of the blood vessels.