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

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 Right 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 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 could try to compensate for this?

Explanation / Answer

The condition of mixing of oxygenated blood and impure blood due to a hole in the septum between the left and right ventricles is called as ventricular septal defect.

a) Pressure in the left ventricle decreases because there is diverted passive flow of the oxygenated blood into the right ventricle due to the hole that is present in the septum between the right and left ventricles.

b) Stroke volume is the volume of blood pumped pumped from left ventricle per beatt. Since there is leakage of blood from the left ventricle into the right ventricle, the total volume of blood that ought to be pumped out of the left ventricle now decreases.

c) Oxygenation of blood in the left ventricle decreases since the total volume of the oxygenated blood that was pumped from the left auricle and which enters in to the left ventricle is different from the amount of blood which leaves the left ventricle into the aorta. This is again due to the leakage of oxygenated blood from the left ventricle into the right ventricle due to the presence of the hole in the septum.

d)

Compensation of the body because of decreased stroke volume was studied by Ernest Starling and colleagues in the early 20th century who found that increasing venous return to the heart , which increased the filling pressure of the ventricle, led to increased stroke volume (SV). Conversely, decreasing venous return decreased stroke volume. This cardiac response to changes in venous return and ventricular filling pressure is intrinsic to the heart . It does not depend on extrinsic neurohumoral mechanisms . This is called the Frank-Starling mechanism (or Starling's Law of the heart) which is ability of the heart to change its force of contraction and therefore stroke volume in response to changes in venous return .

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