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There is a hole in the septum that separates the left ventricle and right ventri

ID: 86965 • Letter: T

Question

There is a hole in the septum that separates the left ventricle and right ventricle: (a) Explain why you would expect the pressure in the left ventricle to decrease and that in the right ventricle to increase. (b) Explain why you would expect the stroke volume from the left ventricle to decrease because of this (c) Explain why the oxygenation of the blood in the left ventricle would decrease and that in the right ventricle would increase. (d) If during systole the (gauge) pressure, stroke volume, and oxygenation Right Left ventricle levels (relative to that in the vena cavae) in the left ventricle each ventricle decreases by 10% as a result of this, explain quantitatively how the body Ventricular could try to compensate for this?

Explanation / Answer

a. The pressure in left ventricle would decrease and that in the right ventricle would increases because when the blood from left ventricle passes to right ventricle a larger volume of blood leaves the left ventricle thus decreasing the pressure. The extra blood then passes into the pulmonary artery from the right ventricle increasing the pressure in the blood vessels of the lungs.

b. Stroke volume is the volume of blood pumped from left ventricle in one contraction. The stroke volume is generally equal for both ventricles approximately 70 ml in a healthy person.

The shunting of blood in VSD increases the right ventricular volume and its output. The increased output leads to pulmonary hypertension.

The increased pulmonary flow of blood leads to enlargement of left atrium. This results in increased left ventricular preload and stroke volume by the Frank-Starling mechanism.

c. Through the hole in the septum there is some level of mixing of blood in both the ventricular chamber. Thus the pure blood mixes with impure blood. This causes the oxygen rich blood from the left ventricle to mix with the oxygen poor blood of the right ventricle. Therefore oxygenation of blood in left ventricle decreases and in right ventricle it increases.

d. There is decrease in systolic pressure, stroke volume, oxygenation of blood in left ventricle in VSD. Our body has developed mechanism to compensate this decrease.

Frank-Starling mechanism- It explains the relationship between the stroke volume and diastolic volume. This law demonstrates that the increase in stroke volume of heart increases in response to an increase in the volume of blood in the ventricles before contraction assuming all other factors to be constant.

According to this law, as a larger volume of blood flows into the ventricle, the cardiac muscle fiber get stretched leading to an increase in the force of contraction. This allows the cardiac output to be in synchronization with the return of venous blood, blood supply from arteries and humoral length. This mechanism helps in maintaining equal left and right ventricular output.

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