Question

Steve is a runner with a target heart rate of 135 bpm. His resting pulse is 70 bpm. His blood volume is approximately 6.8 liters. At rest, his cardiac output is 63 tr/min A What must his stroke volume be? B. What is his EDV if his ESV is 50 ml? C. During his workout, his heart rate increases to 136 born and his cardiac output to 13,500 mL/min. Did his SV change with exercise? If his EDV is 160 during his workout, what is his ESV? D. Why is aferload important to cardiac function? Essay answers are limited to about 500 words (3800 characters maximum, including spaces). 3800 Character(s) remaining

Answer 1

A) Given, that cardiac output at resting state is 6.3 L/min, i.e., 6300 mL/min and the resting heart hert rate is 70bpm. Cardiac output is usually calculated as a product of stroke volume and heart rate. Here, cardiac output and heart rate is given, hence, we can calculate the stroke volume as follows:

CO = SV x HR

6300 = SV x 70 ; SV = 6300/70 = 90mL

B) We have calculated stroke volume as 90 mL and ESV is given as 50 mL. Now, stroke volume can also be calculated as the difference of EDV and ESV. Hence, EDV can be calculated as follows:

SV = EDV - ESV ; 90 = EDV - 50

Therefore, EDV = 140mL.

C) It is given that during workout, the cardiac output changed to 13,500 mL/min and heart rate increased to 135 bpm, hence the new Stroke volume will be 13,500/135 = 100 mL. This new value of stroke volume is higher than the earlier value obtained for resting state.

Also, the EDV during exercise is given as 160mL, hence ESV will be calculated as:

SV = EDV - ESV ; 100 = 160 - ESV

ESV = 60 mL

Thus, Stroke volume during exercise will be 100 mL and ESV will be 60 mL.

D) Afterload is the pressure against which heart has to work to eject blood during ventricular contraction, i.e., systole. It is proportional to the mean arterial pressure. Hence, greater the afterload, greater the effort produced by heart to maintain the blood flow. Similarly, reducing the afterload can increase cardiac output. This is the reason that afterload is important to cardiac function.