Question

1. Consider two blood vessels that have the same length and resistance. Given these pressure
differentials along their lengths, which one will have the greatest flow? Why?
Vessel 1: P1 = 100 mmHg, P2 = 25 mmHg
Vessel 2: P1 = 500 mmHg, P2 = 400 mmHg

2. A healthy student requires a cardiac output of 4000mL per minute to support resting activity. The interval between beats is 0.8 secs.

In moderate exercise, such as walking, the student’s heart rate climbed to 135BPM, end diastolic volume decreased to 100mL and ejection fraction was 80%.

i. What is cardiac output?

ii. Why would end diastolic volume decline under these circumstances?

iii. What other changes may occur with exercise?

Answer 1

Answer 1:)

Blood flow directly depends upon the difference in blood pressure.

The pressure difference in vessel 1 = 100 – 25

The pressure difference in vessel 1 = 75 mmHg

The pressure difference in vessel 2 = 500 – 400

The pressure difference in vessel 2 = 100 mmHg

Therefore, blood flow will be more in the vessel 2 than vessel 1.

Answer 2i:)

Cardiac output calculates by the following formula:

CO = Stroke volume x Heart beat

First, calculate stroke volume by using the following formula:

Stroke volume = Ejection fraction x End- Diastolic Volume

Stroke volume = 80% x 100

Stroke volume = 80 mL

Therefore,

CO = 80 x 135

CO = 10800 mL

Therefore, the cardiac output is 10800 mL.

Answer 2ii:)

Due to the large increase in inotropy, the end-diastolic volume decreases in this condition.

Answer 2iii:)

The other effects due to exercise are increased in end-systolic volume and stroke volume.