Question

You know that stroke volume is the difference between End Diastolic Volume and End Systolic volume. The attending physician in the Cath lab just told you that your patient’s End Systolic Volume has decreased, and their stroke volume has increased. She asks you the following questions. How would you respond?

a.What did the heart do to lower the End Systolic Volume?

b.What two possibilities (mechanisms) could the heart have used to achieve the increase in stroke volume and lower End Systolic Volume?

Answer 1

(a)

The volume of the blood present in the ventricles during the systole (end of the contraction phase) is known as the End-Systolic Volume. The End-Systolic Volume should be decreased so that less blood is left after contraction.

It is influenced by three factors:-

• Starling's Law
• Contractility
• Afterload

The heart lower the End-Systolic Volume as follows:-

• The activity of the Sympathetic Nervous System is increased that results in the increase of the release of the epinephrine, norepinephrine, and neurotransmitters.
• The heart muscles contract harder when the End-Diastolic Volume is increased, thus, more blood is pumped out.
• When more blood is pumped out, less amount of blood is left in the ventricles. Thus, End-Systolic Volume is lower

(b)

The two mechanisms the heart used to lower End-Systolic Volume and increase the Stroke Volume are:-

• Starling's Law- It states that the more the blood entering the heart, the more the contraction of the heart muscles. Thus, increasing the Stroke Volume and decreasing the End-Systolic Volume.
• Contractility- The heart contractility increases when the sympathetic stimulation of the heart increases. This results in the more forceful contraction of the cardiac fibers at all levels of preload. This mechanism increases the stroke volume by decreasing the End-Systolic Volume regardless of the End-Diastolic Volume.