27.6. What types of heart’s overloading can cause the development of cardiac insufficiency?

There are two types of heart’s overloading:

1. The overloading of volume of blood comes to the heart or to its separate cavities. In such conditions the heart or its part which undergoes the overloading must transfer an increased volume of coming blood into arterial system. It is achived by increasing of minute volume of heart in correspondence with increased win’s returning.

The overloading by volume the heart undergoes under such circumstances:

a) an increasing of win’s returning of blood to the heart and specifically during an increasing volume of circulating blood (hypervolemia) or increasing of tone of win’s (a reducing of win’s system volume).

b) valvular disease of the heart – insufficiency of its values. So, during insufficiency of aortal and mitral values develops overloading of the left ventricle and during the insufficiency of the pulmonary artery value and tricuspid value – the overloading of the right ventricle.

2. The overloading by resistance arises when the heart must work against the increased resistance, which obstructs a transferring all the blood into arterial system. During overloading by resistance the heart must maintain its minute volume in spite of the increased resistance to expulsion of the blood.

The overloading by resistance develops under such circumstances:

a) hypertension (high blood pressure or high arterial pressure an increasing of peripheral vessel resistance). During hypertension of systemic circulation the left ventricle undergoes the overloading by resistance and during the hypertension of lesser circulation the right ventricle undergoes the overloading by resistance;

b) valvular diseases of the heart – stenosis of the values’ foramens.

So during the stenosis the aorta’s foramen develops the overloading of the left ventricle and during the stenosis mitral value’s foramen develops the overloading of the left atrium, during the stenosis of the pulmonary artery’s foramen develops the overloading of the right ventricle and during the stenosis of the tricuspid value’s foramen develops the overloading of the right atrium.

27.7. What mechanisms can provide the compensation of heart during the effect of the increased leading on it?

During the effect of the leadings by volume and by resistance on heart increase of the heart’s work is provided by two types of compensatory mechanisms.

I. Urgent mechanisms of compensation of the heart. We can refer to them such mechanisms as:

a) heterometric mechanism;

b) homeometric mechanism;

c) chronoinotropic mechanism;

d) inotropic effect of the catecholamines.

II. Mechanisms of the prolonged adaptation of the heart – the hypertrophy of the miocardium.

27.8. What is the essence of the heterometric mechanism of the compensation of the heart?

Heterometric mechanism is one of the urgent mechanisms of the compensation of the heart to the affect of the leadings by volume.

Its essence is concluded in the increase of the heart contractility’s power in the conditions of the coming an increased volume of the blood to the heart.

The base of the heterometric mechanism is the Franks-Starling law. It (the low) has two formulations: for separate muscular fibers and for the heart in work. An the first variant its essence displays by such statement: the more starting length of the muscular fiber (to some limits), the more the power of its contraction. For the heart in whole there is the following formulation: the more the final diastolic volume of the heart’s ventricles, the more their percussion volume.

The basic displays of the heterometric mechanism of the compensation are an increase of the final diastolic pressure because of the increase of the enlistment of the blood into cavities of the ventricles and increase of the heart because of the increase of the heart contractility power. The tension of the muscular fibers does not change this procedure. The length of the muscular fibers changes and as a result we have a name of the mechanism – final diastolic.