Rhythm of heart. Parameters of cardiac activity.

Rhythm of heart is the quantity of reductions in 1 minute, depends mainly on a functional condition of wandering and sympathetic nerves. At excitation of sympathetic nerves frequency of cardiac reductions increases. This phenomenon is called a tachycardia. Frequency of cardiac reductions decreases at excitation of wandering nerves. This phenomenon is called a bradycardia. A condition of a cerebral cortex influences on the rhythm of heart: at strengthening braking the rhythm of heart is slowed down, at strengthening exciting process is stimulated. The rhythm of heart can change under influence humoral influences, in particular temperatures of blood, affluent to heart. In experiences it has been shown, that the local irritation by heat of area of the right auricle (localization of the leading unit) conducts to increase of a rhythm of heart, at cooling this area of heart the opposite effect is observed. The local irritation by heat or a cold of other sites of heart is not reflected on frequency of cardiac reductions. However it can change speed of carrying out of excitation on conductive system of heart and to be reflected on force of cardiac reductions. Frequency of cardiac reductions at the healthy person is in dependence from age. These data are presented in the table.

Age	Quantity of cardiac reductions in 1 minute
Newborns	120—140
Up to 5	130
5—10	88
10—15	78
15—60	68—72

Parameters of cardiac activity. Parameters of work of heart are systolic and minute volume of heart. Systolic or shock volume is the quantity of blood, which heart throws out in corresponding vessels at each reduction. The size of systolic volume depends on the sizes of heart, a condition of a myocardium and an organism. At the adult healthy person at condition of relative rest systolic volume of everyone ventricle is equal to approximately 70-80 ml. Thus, at reduction ventricles 120-160 ml of blood moves in arterial system. The minute volume of heart is a quantity of blood, which heart throws out in a pulmonary trunk and an aorta for 1 minutes. Average minute volume is 3-5 litres. Systolic and the minute volume of heart characterizes activity of all device of blood circulation.

External displays of activity of heart.

There are data on which the doctor judges about work of heart by external displays of its activity. It is a top push, cardiac tones. Top push. During a systole ventricles heart makes rotary movement, turning from left to right. The top of heart rises and presses on a thorax in the field of the fifth intercostal interval. During a systole heart becomes very dense; therefore pressing of a top of heart on an intercostal interval can be seen (bulging, protrusion). The top push can be probed (to palpate) and to define its borders and force. Cardiac tones are the sound phenomena arising in working heart. It is possible to distinguish two tones: I-systolic and II - diastolic.

Systolic tone. Atrioventricular valves take part in an origin of this tone. During a systole ventricles atrioventricular valves are closed, and fluctuations of their shutters and attached to them tendinous strings cause I tone. Besides the sound phenomena which arise at reduction of muscles ventricles take part in origin I of tone. On sound features I tone is lingering and low.

Diastolic tone arises in the beginning diastole of ventricle during protodiastolic phase, when there is a closing of semilunar valves. Fluctuation of shutters of valves thus is a source of the sound phenomena. Under the sound characteristic II tone is short and high.

Also it is possible to judge about work of heart on the electric phenomena arising in it. Them are called biopotentials of heart and receive by means of electrocardiograph. They carry the name of the electrocardiogram.