A healthy student requires a cardiac output of 5000mL per minute to support rest
ID: 93828 • Letter: A
Question
A healthy student requires a cardiac output of 5000mL per minute to support resting activity. The interval between beats is 0.75 secs. a. What is his heart rate? b. What is his stroke volume? c. Measurements under these conditions show that his end diastolic volume is 150ml. What is his ejection fraction? d. In moderate exercise, such as walking, the student's heart rate climbed to 130BPM, 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? ii) What other changes may occur with exercise?Explanation / Answer
Cardiac output is 5000 ml/min
The intreval between beats is 0.75 secs
a) Heart rate per minute is calculated as follows,
In 0.75 sec, 1 beat occurs
Therefore, the number of beats in 60 seconds is
= 60/0.75
= 80
Heart rate is 80 beats per minute
b) Stroke volume is defined as volume of blood pumped by the left ventricle per beat
Stroke volume is calculated by the formula,
= cardiac output / heart beat per minute
= 5000/80
= 62.5 ml
c) Ejection fraction is defined as the measurement of percentage of blood leaving the heart and is given by the formula,
= amount of blood pumped out of the ventricle / total amount of blood in the heart
= stroke volume / end diastolic volume
= 62.5 / 150
= 41.67%
d) Heart rate = 130 beats per minute
End diastolic volume = 100 ml
Ejection fraction = 80%
So, stroke volume = end diastolic volume x ejection fraction
= 100 x 0.8
= 80 ml
i) cardiac output = stroke volume x heart rate per minute
= 80 x 130
= 10,400 ml
ii) End diastolic volume decreases due to arteriolar dilatation and decreased peripheral resistence during exercise.
iii) Some other changes which occur during exercise are,
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