Question

List the effect on cardiac output, SV, HR, EDV, and/or ESV and describe why this change occurred for each of the following cases:

1. an increase in sympathetic autonomic stimulation
2. an increase in afterload
3. a decrease in end diastolic volume

Answer 1

a) SV increases, HR increases, EDV increases ESV decease.and cardiac output increases

b.) SV decreases, HR decreases, EDV decreases ESV increases and cardiac output decreases

c) SV decreases, HR decrease, ESV increases and cardiac output decreases.

Sympathetic nerves innervates the myocardium, increases in sympathetic activity increase myocardial contractility and, therefore, increase stroke volume.

Cardiac output is the total volume of blood pumped by the heart per minute. It is the product of blood pumped by each heart beat (stroke volume or SV) and the number of beats (heart rate HR) So on sympathetic stimulation there is also increase in HR and cardiac output.

End diastolic volume (EDV) is the amount of blood in the ventricle right before contraction and End systolic volume (ESV) is the amount of blood left inthe ventricles after ventricular contraction.

According Frank starling mechanism, if the heart is filled with more blood, this will cause stronger contraction, sending more blood out of the heart, this increases the stroke volume even further by decreasing ESV and increasing EDV.

b) Afterload is increased when aortic pressure and systemic vascular resistance are increased,  When afterload increases, there is an increase in end-systolic volume and a decrease in stroke volume.