Characteristics of the circulatory system for children

2021-01-30 12:00 AM

An infant's heart is relatively larger than that of an infant's and accounts for 0.8% of body weight. After 1 year, the development of the heart is proportional to the development of the child's height and weight and accounts for 0.5% of body weight.

Characteristics of placenta circulation and postpartum circulation

Fetal circulation

Placenta circulation is formed from the end of the second month, continues to develop and damage until after delivery.

The placenta circulation is not completely separated into 2 cycles: the circulatory system and the microcirculation, because they communicate with each other through:

Bottle hole in the atrial septum (oval hole).

The Bottle tube (ductus arteriosus) connects the aorta and the pulmonary artery.

Therefore, the blood that goes to feed the fetus is mixed blood.

Circulation after childbirth

From the time of umbilical cord cut, the circulatory system and the microcirculation really are separated by:

The Bottle tube gradually becomes blocked by 6-11 weeks postpartum to become the aortic ligament.

The Bottle hole closes gradually from 5 to 7 months postpartum.

The baby begins to breathe, the lungs begin to function in gas exchange.

Blood to feed the body is arterial blood.

Physical characteristics of the heart and blood vessels


An infant's heart is relatively larger than that of an infant's and accounts for 0.8% of body weight. After 1 year, the development of the heart is proportional to the growth of the child's height and weight and accounts for 0.5% of the body weight.

Heart position and posture: The first months of the heart are horizontal, lying high, lying near the middle of the chest slightly to the left; at 1 year of age, the heart lies on its side from top to bottom, from right to left; After 4 years the posture of the heart is the same as that of an adult.

Cardiomyopathy: Infants, the right ventricular wall is approximately the same thickness as the left ventricular wall (about 5mm). After 14 years of development, the left ventricular wall increased by 5 mm, while the right ventricle wall increased only 1 mm. The younger the child, the weaker the heart muscle, so when there is an increase in burden, it is easy to have heart failure.

Cardiac distortion (straight scan) on the radiograph of infant’s accounts for 50%, older children account for less than 50% of the horizontal diameter (side - side) of the pectoral.

Blood vessel

The aorta and pulmonary lumen in children vary with age:

Before 10-12 years: Pulmonary artery> Aorta.

From 10-12 to puberty: Pulmonary artery = Aorta.

After puberty: Pulmonary artery <Aorta.

The aortic lumen and ventricular dimensions (in mm) develop unevenly with age:

Newborn: 20: 25

10 years old: 56: 140

Children at puberty: 61: 260

The younger the capillaries are, the larger they are relative to those of the older ones, and for the pulmonary capillaries, kidneys, skin, and intestines, they are significantly larger.

The above characteristics are aimed at meeting the needs of oxygen and nutrition in children, which are higher than those in adults, and create low blood pressure, gaping red skin, but also easily causing vascular collapse.

Basic indicators of hemodynamics

Circuit frequency

The younger the baby, the faster the pulse, the more easily changed when stimulated, when exertion (sucking, crying, fever). So, need to take the pulse at quiet or at bedtime.

Table: Circuit frequency of children of different ages.


Circuit frequency



6 months

130- 135

12 months

120 - 125

2 years old

110- 115

3 years old

105 - 110

4 years old

100 - 105

5 years old


6 year old

90- 95

7 years old

85 - 90

8-11 years old

80- 85

12-13 years old

75 - 80

14-16 years old

70- 75

Arterial blood pressure

The younger the baby, the lower the blood pressure of the arteries: - Maximum blood pressure:

Infant: 70mmHg

Child 1 year (12 months): 80mmHg

Children> 1 year old are calculated by the formula:

Maximum blood pressure = 80 + 2n

(n: age number)

Minimum blood pressure:

Blood pressure min = Max blood pressure / 2 + K

Digital K depends on age:

Children <7 years: 10.

Children 7-12 years: 15.

Children 13-15 years old: 20.


The circulation cycle in children is shorter than that in adults. The time it takes to complete a full cycle is:

Newborn: 12 seconds.

Children 3 years: 15 seconds.

14 years old: 18 seconds.

Adult: 22 seconds.

Circulating blood volume

Circulating blood volume by weight in children is greater than that of adults:

Newborn: 110-150ml / kg.

Children under 1 year old: 75-100ml / kg.

Children from 1 year old and older: 50-90ml / kg.